Neurology_Adams

Neurology_Adams. Variations in regional anatomy could explain these several postulated mechanisms, but to this day there is not full agreement about the validity of anterior scalene and costoclavicular syndromes. An anomalous cervical rib, which arises from the seventh cervical vertebra and extends laterally between the anterior and medial scalene muscles and then under the brachial plexus and subclavian artery to attach to the first rib, obviously disturbs the anatomic relationships of these structures and may compress them (Fig. 10-7). However, as an estimated 1 percent of the population has cervical ribs, usually on both sides, and only about 10 percent of these persons have neurologic or vascular symptoms (almost always one-sided), other factors must be operative.


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Neurology_Adams. The anterior and middle scalene muscles, which flex and rotate the neck, are both inserted into the first rib so that the subclavian artery and vein and the brachial plexus must pass between them. Hence abnormalities of insertion and hypertrophy of these muscles were once thought to be causes of the syndrome but sectioning them (scalenectomy) has so rarely altered the symptoms that this mechanism is no longer given credence. Three neurovascular syndromes are associated with a rudimentary cervical rib (rarely with a complete cervical rib) and related abnormalities at the thoracic outlet: subclavian venous or arterial compression and a brachial plexopathy. In all three forms, shoulder and arm pain is prominent. The discomfort is of the aching type and is felt in the posterior hemithorax, pectoral region, and upper arm. These syndromes sometimes coexist, but more often each occurs independently.


Neurology_Adams

Neurology_Adams. Compression or spontaneous thrombosis of the subclavian vein is a rare occurrence causing a dusky discoloration, venous distention, and edema of the arm. The vein may become thrombosed after prolonged exercise (Paget-Schrötter syndrome) or in cases of a clotting diathesis in cancer patients. Compression of the subclavian artery, which results in ischemia of the limb, may be complicated by digital gangrene and retrograde embolization, also is a rare entity. A unilateral Raynaud phenomenon, brittle nails, and ulceration of the fingertips are important diagnostic findings. A supraclavicular bruit is suggestive but not in itself diagnostic of subclavian artery compression.


Neurology_Adams

Neurology_Adams. The conventional tests for vascular compression—obliteration of the pulse when the patient, seated and with the arm extended, takes and holds a full breath, tilts the head back, and turns it to the affected side (Adson test) or abducts and externally rotates the arm and braces the shoulders and turns the head to either side (Wright maneuver)—are not entirely reliable. Sometimes these maneuvers fail to obliterate the radial pulse in cases of proved compression; contrariwise, these tests may be positive in normal persons. Nevertheless, a positive test only on the symptomatic side (with reproduction of the patient’s symptoms) is suggestive of the diagnosis of arterial compression and, by implication, some form of thoracic outlet syndrome. Plethysmographic recording of the radial pulse and ultrasound of the vessel add greatly to the accuracy of these positional tests.


Neurology_Adams

Neurology_Adams. A primarily neurologic problem may characterize the thoracic outlet syndrome. There is slight wasting and weakness of the hypothenar, interosseous, adductor pollicis, and deep flexor muscles of the fourth and fifth fingers (i.e., the muscles innervated by the lower trunk of the brachial plexus and ulnar nerve). Weakness of the flexor muscles of the forearm may be present in advanced cases. Tendon reflexes are usually preserved. In addition, most patients complain of an intermittent aching of the arm, particularly of the ulnar side, and about half of them complain also of numbness and tingling along the ulnar border of the forearm and hand. A loss of superficial sensation in these areas is variable. It may be possible to reproduce the sensory symptoms by firm pressure just above the clavicle or by traction on the arm. Vascular features are often absent or minimal in patients with the neurologic form of the syndrome.


Neurology_Adams

Neurology_Adams. In patients with neurologic signs, nerve conduction studies disclose reduced amplitude of the ulnar sensory potentials. There may be decreased amplitude of the median motor evoked potentials as well, a mild but uniform slowing of the median motor conduction velocity, and a prolongation of the F-wave latency. Concentric needle examination of affected hand muscles reveals large-amplitude motor units, suggesting collateral reinnervation. Somatosensory evoked potentials may be a useful adjunct to the conventional nerve conduction and EMG studies (Yiannikas and Walsh). Brachial artery MR angiography is usually reserved for patients with a suspected arterial occlusion, an aneurysm, or an obvious cervical rib. The place of venography in the diagnostic workup is uncertain, for a number of otherwise normal individuals can occlude the subclavian vein by fully abducting the arm.


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Neurology_Adams. In the authors’ experience, unambiguous instances of thoracic outlet syndrome are not common. This has also been the experience of Wilbourn, whose review of this subject is recommended. One should be skeptical of the diagnosis unless the clinical and EMG features enumerated above are present. Common mistakes are to confuse the thoracic outlet syndrome with carpal tunnel syndrome, ulnar neuropathy or entrapment at the elbow, or cervical radiculopathy caused by arthritis or disc disease. Brachial neuritis may have a similar presentation. Imaging studies and careful nerve conduction and EMG studies may be necessary to exclude all of these disorders. Treatment of the Thoracic Outlet Syndrome


Neurology_Adams

Neurology_Adams. Treatment of the Thoracic Outlet Syndrome A conservative approach is advisable. If the main symptoms are pain and paresthesia, Leffert suggests the use of local heat, analgesics, muscle relaxants, and an assiduous program of special exercises to strengthen the shoulder muscles. A full range of neck motions is then practiced. On such a regimen, some patients experience a relief of symptoms after 2 to 3 weeks. Instruction by a qualified physical therapist is invaluable.


Neurology_Adams

Neurology_Adams. Only if pain is severe and persistent and is clearly associated with the vascular or neurogenic features of the syndrome is surgery indicated. The usual approach is through the supraclavicular space, with cutting of fibrous bands and excision of the rudimentary rib. In cases of venous or minor arterial forms of the syndrome, some thoracic surgeons favor the excision of a segment of the first rib through the axilla. Pain is often dramatically relieved, but the sensorimotor defects improve only slightly. Sectioning of the scalenus muscle is not endorsed because, as already noted, the role of muscle in causing thoracic outlet syndrome has been questioned. Other Painful Conditions Originating in the Neck, Brachial Plexus, and Shoulder The brachial plexus is an important source of shoulder and arm pain. The main disorders are brachial neuritis and metastatic infiltration and radiation damage to the plexus. Chapter 44 discusses these disorders in detail.


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Neurology_Adams. Metastases to the cervical region of the spine are less common than to other parts of the vertebral column. They are, however, frequently painful and may cause root compression. Posterior extension of the tumor from the vertebral bodies or compression fractures may lead to the rapid development of quadriplegia. The Pancoast tumor, usually a squamous cell carcinoma in the superior sulcus of the lung, may implicate the lower cervical and upper thoracic (T1 and T2) spinal nerves as they exit the spine. In these cases, a Horner syndrome, numbness of the inner side of the arm and hand, and weakness of all muscles of the hand and of the triceps muscle are combined with pain beneath the upper scapula and in the arm. The neurologic abnormalities may occur long before the tumor becomes visible radiographically.


Neurology_Adams

Neurology_Adams. Shoulder injuries (rotator cuff), subacromial or subdeltoid bursitis, periarthritis or capsulitis (frozen shoulder), tendonitis and arthritis, as has been mentioned, may develop in patients who are otherwise well, but these conditions also occur as complications of hemiplegia. The pain tends to be severe and extends toward the neck and down the arm into the hand. The dorsum of the hand may tingle without other signs of nerve involvement. Immobility of an arm following myocardial infarction may be associated with pain in the shoulder and arm and with vasomotor changes and secondary arthropathy of the hand joints (shoulder–hand syndrome); after a time, osteoporosis and atrophy of cutaneous and subcutaneous structures occur (Sudeck atrophy or Sudeck-Leriche syndrome). Similar changes may occur in the foot and leg, or all articular structures on the side of a hemiplegia, or in association with the painful lesions described in the first part of this chapter. The neurologist should know


Neurology_Adams

Neurology_Adams. occur in the foot and leg, or all articular structures on the side of a hemiplegia, or in association with the painful lesions described in the first part of this chapter. The neurologist should know that these complications can be prevented by proper exercises and relieved by cooling of the affected limb.


Neurology_Adams

Neurology_Adams. Vasomotor, sudomotor, and trophic changes in the skin, with atrophy of the soft tissues and decalcification of bone, may follow the prolonged immobilization and disuse of an arm (i.e., frozen shoulder syndrome) or leg for whatever reason. Medial and lateral epicondylitis (tennis elbow) are readily diagnosed by demonstrating tenderness over the affected parts and an aggravation of pain on certain movements of the wrist. We have observed entrapment of the ulnar nerve in some cases of medial epicondylitis. The pain of the carpal tunnel syndrome often extends into the forearm and sometimes into the anterior biceps region and may be mistaken for disease of the shoulder or neck. Similarly, involvement of the ulnar, radial, or median nerves may be mistaken for brachial plexus or root lesions. EMG and nerve conduction studies are helpful in these circumstances (this common disorder is discussed in Chap. 44). Polymyalgia Rheumatica (See Also Chap. 9)


Neurology_Adams

Neurology_Adams. Polymyalgia Rheumatica (See Also Chap. 9) This syndrome is observed in middle-aged and elderly persons and is characterized by severe pain, aching, and stiffness in the proximal muscles of the limbs and a markedly elevated erythrocyte sedimentation rate. The shoulders are most affected, but half of these patients have hip or neck pain as well. Constitutional symptoms (loss of weight, fever, and anemia) and articular swelling are less consistent manifestations. A few patients have pitting edema of the hands or feet, as illustrated in the review by Salvarini and colleagues; others have knee or wrist arthritis or carpal tunnel syndrome. Arthroscopy and MRI suggest that the pain originates in a synovitis or, sometimes more accurately, a bursitis, and in an inflammation of periarticular structures. The fundamental cause is not known.


Neurology_Adams

Neurology_Adams. Activity of the disease correlates with elevation of the sedimentation rate, almost always above 40 mm/h and typically higher than 70 mm/h (and corresponding elevation of C-reactive protein); unlike the case in polymyositis, with which it is confused, creatine kinase levels are normal. In many patients, polymyalgia rheumatica is associated with giant cell (temporal, or cranial) arteritis. The precise concordance of these two allied conditions is not known but there is not a high frequency of overlap. The arteritis may affect one or both optic nerves; blindness is the main risk of the disease, as discussed in detail in Chap. 13.


Neurology_Adams

Neurology_Adams. Treatment This disorder is self-limiting, lasting 6 months to 2 years, and responds dramatically to corticosteroid therapy, although this may have to be continued in low dosage for several months or a year or longer. We begin treatment with 20 mg of prednisone if there is no evidence of temporal arteritis (which requires higher doses). The absence of improvement in a day or two should bring the diagnosis into question. The degree of hip and shoulder pain is the best guide to the duration of steroid therapy and the rate at which the drug is withdrawn, usually in very small increments every 2 weeks. The sedimentation rate or C-reactive protein can be used as a guide, but neither alone is adequate to alter the medication schedule. Complex Regional Pain Syndrome (Reflex Sympathetic Dystrophy and Causalgia; (See Chap. 7)


Neurology_Adams

Neurology_Adams. This painful response to injury of the shoulder, arm, or leg, is usually the result of an incomplete nerve injury. It consists of protracted pain, characteristically described as “burning,” together with cyanosis or pallor, swelling, coldness, pain on passive motion, osteoporosis, and marked sensitivity of the affected part to tactile stimulation. The condition has been variously described under such terms as Sudeck atrophy, posttraumatic osteoporosis (in which case the bone scan may show increased local uptake of radioactive nuclide), and the related shoulder–hand syndrome. The current term is complex regional pain syndrome. When the pain syndrome occurs in isolation, it is referred to as causalgia. Pharmacologic or surgical sympathectomy appears to relieve the symptoms in some patients. In others with a hypersensitivity of both C-fiber receptors and postganglionic sympathetic fibers, it is not helpful. Chapter 8 discusses this subject further.


Neurology_Adams

Neurology_Adams. Persistent and often incapacitating pain and dysesthesias may follow any type of injury that leads to partial or complete interruption of a nerve, with subsequent neuroma formation or intraneural scarring—fracture, contusion of the limbs, compression from lying on the arm while intoxicated, severing of sensory nerves in the course of surgical operations or biopsy of nerve, or incomplete regeneration after nerve suture. It is stated that the nerves in these cases contain a preponderance of unmyelinated C fibers and a reduced number of A-c fibers; this imbalance is presumably related to the genesis of painful dysesthesias. These cases are best managed by complete excision of the neuromas with end-to-end suture of healthy nerve, but not all cases lend themselves to this procedure.


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Neurology_Adams. Another special type of neuroma is the one that forms at the end of a nerve severed at amputation (stump neuroma). Pain from this source is occasionally abolished by relatively simple procedures such as injection of lidocaine, resection of the distal neuroma, proximal neurotomy, or resection of the regional sympathetic ganglia. More common in clinical practice is the mundane, but painful, Morton neuroma, usually found on the plantar nerve between the third and fourth metatarsal bones. Pain on compression of the forefoot is the characteristic Mulder sign.


Neurology_Adams

Neurology_Adams. This rare disorder of the microvasculature produces a burning pain and bright red color change, usually in the toes and forefoot and sometimes in the hands, precipitated by changes in ambient temperature. Since its first description by Weir Mitchell in 1878, many articles have been written about it, and recently the cause of a primary familial form was traced to a mutation in a sodium channel protein. Each patient has a temperature threshold above which symptoms appear and the feet become bright red, warm, and painful. The afflicted patient rarely wears stockings or regular shoes because these tend to bring out the symptoms. The pain is relieved by walking on a cold surface or soaking the feet in ice water and by rest and elevation of the legs. The peripheral pulses are intact, and there are no motor, sensory, or reflex changes. The reviews by Michiels and by Layzer are recommended.


Neurology_Adams

Neurology_Adams. Most cases are idiopathic, some familial and inherited as a dominant trait. There are secondary forms of the disease, the most important one being that associated with essential thrombocythemia (up to 25 percent of patients may have erythromelalgia as the first symptom) but also with other myeloproliferative disorders such as polycythemia vera and with collagen vascular diseases, including thrombotic thrombocytopenic purpura (TTP), during the use of calcium channel blockers and certain dopaminergic agonists such as pergolide and bromocriptine, and with occlusive vascular diseases. Some instances arise as a result of a painful polyneuropathy that predominantly affects the small sensory fibers; more often in these latter conditions, the redness and warmth are constant and the result of damage to sympathetic nerve fibers; see Chap. 43. These symptomatic forms have led some experts to question whether erythromelalgia is a type of neuropathy (Davis et al).


Neurology_Adams

Neurology_Adams. Chap. 43. These symptomatic forms have led some experts to question whether erythromelalgia is a type of neuropathy (Davis et al). The familial form of erythromelalgia has been traced to a mutation in a sodium channel (NaV 1.7) that is selectively expressed in dorsal root ganglia nociceptive neurons. In addition to its inherent value in explaining the manifestations of this disease, the discovery of this channelopathy has evinced interest in novel ways to treat pain by manipulating sodium channels.


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Neurology_Adams. Treatment According to Abbott and to Mitts and others, aspirin is useful in the treatment of paroxysms of secondary erythromelalgia and of some primary cases as well; others had recommended methysergide, which has fallen out of use because of retroperitoneal and cardiac valvular fibrosis. Even small doses of aspirin provide relief within an hour, lasting for several days, a feature that is diagnostic. Sano and colleagues report that cyclosporine was of great benefit in a case of familial erythromelalgia that had not responded to other medications.


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Neurology_Adams. A similar condition, restricted in topography to the region of an acquired single nerve or skin injury, has been described by Ochoa under the term ABC syndrome (angry, backfiring C-nociceptors). Episodes of pain and cutaneous vasodilatation were induced by mechanical or thermal stimulation and relieved by cooling. There may be persistent hyperalgesia over the affected area. Lance has suggested that a similar mechanism is operative in the “red ear syndrome” as a result of irritation of the third cervical root.


Neurology_Adams

Neurology_Adams. A confusing problem in the differential diagnosis of neck and limb pain is posed by the patient with pains that are clearly musculoskeletal in origin but are not attributable to a disease of the spine, articular structures, or nerves. The pain is localized to certain vague points in skeletal muscles, particularly the large muscles of the neck and shoulder girdle, arms, and thighs. We have been unable to corroborate the ill-defined tender nodules or cords (trigger points) that have been reported as an essential element of this illness. Excision of such nodules has not revealed any sign of inflammation or other disease process. The currently fashionable terms myofascial pain syndrome, fibromyalgia, and fibrositis have been attached to the syndrome. Many of the patients are middle-aged women, who also have the equally vague chronic fatigue syndrome (myalgic encephalopathy). Some relief is afforded by interventions such as local anesthetic injection, administration of local coolants,


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Neurology_Adams. who also have the equally vague chronic fatigue syndrome (myalgic encephalopathy). Some relief is afforded by interventions such as local anesthetic injection, administration of local coolants, stretching of underlying muscles (“spray and stretch”), and massage, but the results in any given individual are unpredictable and the status of the disorder is not settled.


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Neurology_Adams. Abbott KH, Mitts MG: Reflex neurovascular syndromes. In: Vinken PJ, Bruyn GW (eds): Handbook of Clinical Neurology, vol 8. Amsterdam, North-Holland, 1970, pp 321–356. Barzouhi A, Vieggeert-Lankamp CL, Njeholt GJ, et al: Magnetic resonance imaging on follow-up assessment of sciatica. N Engl J Med 368:999, 2013. Buchbinder R, Osborne RH, Ebling PR, et al: A randomized trial of vertebroplasty for painful osteoporotic vertebral fractures. N Engl J Med 361:557, 2009. Carette S, Leclaire R, Marcoux S, et al: Epidural corticosteroid injections for sciatica due to herniated nucleus pulposus. N Engl J Med 336:1634, 1997. Carette S, Marcoux S, Truchon R, et al: A controlled trial of corticosteroid injections into facet joints for chronic low back pain. N Engl J Med 325:1002, 1991. Cherkin DC, Devo RA, Battié M: A comparison of physical therapy, chiropractic manipulation, and provision of an educational booklet for the treatment of patients with low back pain. N Engl J Med 339:1021, 1998.


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Neurology_Adams. Coppes MH, Marani E, Thomeer RTWM: Innervation of annulus fibrosus in low back pain. Lancet 1:189, 1990. Cuckler JM, Bernini PA, Wiesel SW, et al: The use of epidural steroids in the treatment of lumbar radicular pain. J Bone Joint Surg Am 67:63, 1985. Davis MD, Sandroni P, Rooke TW, Law PA: Erythromelalgia: vasculopathy, neuropathy, or both. Arch Dermatol 139:1337, 2003. Ensrud KE, Schousboe JT: Clinical practice; Vertebral fractures. New Engl J Med 364:1643, 2011. Epstein NE, Epstein JA, Carras R, Hyman RA: Far lateral lumbar disc herniations and associated structural abnormalities: an evaluation in 60 patients of the comparative value of CT, MRI and myelo-CT in diagnosis and management. Spine 15:534, 1990. Evans BA, Stevens JC, Dyck PJ: Lumbosacral plexus neuropathy. Neurology 31:1327, 1981. Finneson BE: Low Back Pain, 2nd ed. Philadelphia, Lippincott, 1981.


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Neurology_Adams. Evans BA, Stevens JC, Dyck PJ: Lumbosacral plexus neuropathy. Neurology 31:1327, 1981. Finneson BE: Low Back Pain, 2nd ed. Philadelphia, Lippincott, 1981. Friedly JL, Comstock BA, Turner JA, et al: A randomized trial of epidural glucocorticoids injections for spinal stenosis. N Engl J Med 371:11, 2014. Friis ML, Bulliksen GC, Rasmussen P: Distribution of pain with nerve root compression. Acta Neurochir (Wien) 39:241, 1977. Ghogawala Z, Dziura J, Butler, W, et al: Decompression and fusion versus laminectomy for lumbar spondylolisthesis. N Engl J Med 2016 Hadler NM, Curtis P, Gillings DB: A benefit of spinal manipulation as adjunctive therapy for acute low-back pain: a stratified controlled trial. Spine 12:703, 1987. Hagen KD, Hilde G, Jamtveldt G, Winnem MF: The Cochrane review of bed rest for acute low back pain. Spine 25:2932, 2000. Hassler O: The human intervertebral disc: a micro-angiographical study on its vascular supply at various ages. Acta Orthop Scand 40:765, 1970.


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Neurology_Adams. Hassler O: The human intervertebral disc: a micro-angiographical study on its vascular supply at various ages. Acta Orthop Scand 40:765, 1970. Hudgkins WR: The crossed straight leg raising sign (of Fajersztajn). N Engl J Med 297:1127, 1977. Jensen MC, Brant-Zawadzki MN, Obuchowski N, et al: Magnetic resonance imaging of the lumbar spine in people without back pain. N Engl J Med 331:69, 1994. Kallmes DE, Comstock BA, Heagarty PJ, et al: A randomized trial of vertebroplasty for osteoporotic spinal fractures. New Engl J Med 361:69, 2009. Kellgren JH: On the distribution of pain arising from deep somatic structures with charts of segmental pain areas. Clin Sci 4:35, 1939. Kelsey JL, White AA: Epidemiology and impact of low back pain. Spine 5:133, 1980. Kopell HP, Thompson WA: Peripheral Entrapment Neuropathies. Baltimore, Williams & Wilkins, 1963. Kristoff FV, Odom GL: Ruptured intervertebral disc in the cervical region. Arch Surg 54:287, 1947.


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Neurology_Adams. Kopell HP, Thompson WA: Peripheral Entrapment Neuropathies. Baltimore, Williams & Wilkins, 1963. Kristoff FV, Odom GL: Ruptured intervertebral disc in the cervical region. Arch Surg 54:287, 1947. Lance JW: The red ear syndrome. Neurology 47:617,1996. LaRocca H: Acceleration injuries of the neck. Clin Neurosurg 25:209, 1978. Layzer RB: Hot feet: erythromelalgia and related disorders. J Child Neurol 16:199, 2001. Leffert RD: Thoracic outlet syndrome. In: Omer G, Springer M (eds): Management of Peripheral Nerve Injuries. Philadelphia, Saunders, 1980. Leyshon A, Kirwan EO, Parry CB: Electrical studies in the diagnosis of compression of the lumbar root. J Bone Joint Surg Br 63B:71, 1981. Lilius G, Laasonen EM, Myllynen P, et al: Lumbar facet joint syndrome: a randomized clinical trial. J Bone Joint Surg Br 71:681, 1989. Long DM: Low-back pain. In: Johnson RT, Griffin JW (eds): Current Therapy in Neurologic Disease, 5th ed. St. Louis, Mosby, 1997, pp 71–76.


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Neurology_Adams. Long DM: Low-back pain. In: Johnson RT, Griffin JW (eds): Current Therapy in Neurologic Disease, 5th ed. St. Louis, Mosby, 1997, pp 71–76. Love JG, Schorn VG: Thoracic-disc protrusions. JAMA 191:627, 1965. Malleson A: Whiplash and Other Useful Illnesses. Montreal, McGill-Queen’s University Press, 2002. Matthews WB: The neurological complications of ankylosing spondylitis. J Neurol Sci 6:561, 1968. McCall IW, Park WM, O’Brian JP: Induced pain referral from posterior lumbar elements in normal subjects. Spine 4:441, 1979. Meade TW, Dyer S, Browne W, et al: Low back pain of mechanical origin: randomised comparison of chiropractic and hospital out-patient treatment. BMJ 300:1431, 1990. Michiels JJ, Van Joost TH, Vuzevski VD: Idiopathic erythromelalgia: A congenital disorder. J Am Acad Dermatol 21:1128, 1989. Mixter WJ, Barr JS: Rupture of the intervertebral disc with involvement of the spinal canal. N Engl J Med 211:210, 1934.


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Neurology_Adams. Mixter WJ, Barr JS: Rupture of the intervertebral disc with involvement of the spinal canal. N Engl J Med 211:210, 1934. Ochoa JL: Pain mechanisms and neuropathy. Curr Opin Neurol 7:407, 1994. Peul WC, van Houweilingen HC, van den Hout WB, et al: Surgery versus prolonged conservative treatment for sciatica. N Engl J Med 356:356, 2007. Postacchini F, Urso S, Ferro L: Lumbosacral nerve-root anomalies. J Bone Joint Surg Am 64A:721, 1982. Powell MC, Szypryt P, Wilson M, et al: Prevalence of lumbar disc degeneration observed by magnetic resonance in symptomless women. Lancet 2:1366, 1986. Quiles M, Marchisello PJ, Tsairis R: Lumbar adhesive arachnoiditis: etiologic and pathologic aspects. Spine 3:45, 1978. Reynolds AF, Weinstein PR, Wachter RD: Lumbar monoradiculopathy due to unilateral facet hypertrophy. Neurosurgery 10:480, 1982. Ropper AH, Zafonte RD: Sciatica. N Engl J Med 372:1240, 2015.


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Neurology_Adams. Reynolds AF, Weinstein PR, Wachter RD: Lumbar monoradiculopathy due to unilateral facet hypertrophy. Neurosurgery 10:480, 1982. Ropper AH, Zafonte RD: Sciatica. N Engl J Med 372:1240, 2015. Salvarini C, Cantini F, Boiardi L, Hunder GG: Polymyalgia rheumatica and giant-cell arteritis. N Engl J Med 347: 261, 2002. Sano S, Itami S, Yoshikawa K: Treatment of primary erythromelalgia with cyclosporine. N Engl J Med 349:816, 2003. Shannon N, Paul EA: L4/5, L5/S1 disc protrusions: analysis of 323 cases operated on over 12 years. J Neurol Neurosurg Psychiatry 42:804, 1979. Sinclair DC, Feindel WH, Weddell G, et al: The intervertebral ligaments as a source of segmental pain. J Bone Joint Surg 30B:515, 1948. Tarlov IM: Perineurial cysts of the spinal nerve roots. Arch Neurol Psychiatry 40:1067, 1938. Tudler MW, Cherkin DC, Berman B, et al: Acupuncture for low back pain. Cochrane Database Syst Rev 2:CD001351, 2000.


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Neurology_Adams. Tudler MW, Cherkin DC, Berman B, et al: Acupuncture for low back pain. Cochrane Database Syst Rev 2:CD001351, 2000. van Gelderen C: Ein orthotisches (lordotisches) Kaudasyndrom. Acta Psychiatr Neurol Scand 23:57, 1948. Verbiest H: A radicular syndrome from developmental narrowing of the lumbar vertebral canal. J Bone Joint Surg Br 36B:230, 1954. Vroomen PC, de Krom MC, Knottnerus JA. Predicting the outcome of sciatica at short-term follow-up. Br J Gen Pract 52:119, 2002. Vroomen P, DeKrom M, Wilmink JT, et al: Lack of effectiveness of bed rest for sciatica. N Engl J Med 340:418, 1999. Weinstein JN, Tosteson TD, Lurie JD, et al: Surgical versus nonsurgical treatment for lumbar spinal stenosis. N Engl J Med 358:794, 2008. Weinstein JN, Tosteson TD, Lurie JD, et al: Surgical vs nonoperative treatment for lumbar disk herniation. The spine patients outcomes research trial (SPORT): a randomized trial. JAMA 296:2441, 2006.


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Neurology_Adams. Weir BKA, Jacobs GA: Reoperation rate following lumbar discectomy. Spine 5:366, 1980. White AH, Derby R, Wynne G: Epidural injections for the diagnosis and treatment of low-back pain. Spine 5:78, 1980. Wilbourn AJ: The thoracic outlet syndrome is overdiagnosed. Arch Neurol 47:328, 1990. Wilbourn AJ: Thoracic outlet syndromes: plea for conservatism. Neurosurg Clin N Am 2:235, 1991. Wray CC, Easom S, Hoskinson J: Coccydynia: aetiology and treatment. J Bone Joint Surg Br 73B:335, 1991. Yiannikas C, Walsh JC: Somatosensory evoked responses in the diagnosis of the thoracic outlet syndrome. J Neurol Neurosurg Psychiatry 46:234, 1983. Yoss RE, Corbin KB, MacCarty CS, Love JG: Significance of symptoms and signs in localization of involved root in cervical disc protrusion. Neurology 7:673, 1957.


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Neurology_Adams. Yoss RE, Corbin KB, MacCarty CS, Love JG: Significance of symptoms and signs in localization of involved root in cervical disc protrusion. Neurology 7:673, 1957. Figure 10-1. A. The lumbar vertebrae viewed from above B. from the side and C. mid-sagittally. A and B show the bony structures and their relationships to the disc space, facet joints and intervertebral foramina. C demonstrates in a cutaway mid-sagittal view, the main ligamentous structures of the spine in relation to the bones and discs. The ligaments and articulations are critical to the mechanical integrity of the spinal column.


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Neurology_Adams. Figure 10-2. (1) Costovertebral angle. (2) Spinous process and interspinous ligament. (3) Region of articular facet (fifth lumbar to first sacral). (4) Dorsum of sacrum. (5) Region of iliac crest. (6) Iliolumbar angle. (7) Spinous processes of fifth lumbar and first sacral vertebrae (tenderness = faulty posture or occasionally spina bifida occulta). (8) Region between posterior superior and posteroinferior spines. Sacroiliac ligaments (tenderness = sacroiliac sprain, often tender, with fifth lumbar or first sacral disc). (9) Sacrococcygeal junction (tenderness = sacrococcygeal injury; i.e., sprain or fracture). (10) Region of sacrosciatic notch (tenderness = fourth or fifth lumbar disc rupture and sacroiliac sprain). (11) Sciatic nerve trunk (tenderness = ruptured lumbar disc or sciatic nerve lesion).


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Neurology_Adams. Figure 10-3. Mechanisms of compression of the fifth lumbar and first sacral roots. A lateral disc protrusion at the L4-L5 level usually involves the fifth lumbar root and spares the fourth; a protrusion at L5-S1 involves the first sacral root and spares the fifth lumbar root. Note that a more medially placed disc protrusion at the L4-L5 level (cross-hatched) may involve the fifth lumbar root as well as the first (or second and third) sacral root.


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Neurology_Adams. Figure 10-4. Lumbar disc herniation as shown by T2-weighted MRI. A. Sagittal view of a large herniated nucleus pulposus at L5-S1. The posteriorly protruding disc material indents and elevates the anterior thecal sac and narrows the spinal canal. The extruded material has the same signal characteristics of the parent disc. The disc space at this level is narrowed and the disc is less hyperintense than normal because of desiccation and the extruded component. B. Axial view showing the focal right paracentral posterior disc herniation (large arrow) protruding into the canal and compressing the traversing nerve root (the right S1 nerve root) at this level. The exiting L5 roots above are not affected and can be seen laterally to the disc (small arrows).


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Neurology_Adams. Figure 10-5. Lumbosacral MRI of a patient with lymphoma, with radiation-induced arachnoiditis causing severe back pain and leg weakness. A. Sagittal T2-weighted MRI showing clumping of the nerve roots of the cauda equina. B. Axial T2-weighted image at the L3 vertebral level showing clumping of the nerve roots. C. Axial T2-weighted image at the L5 vertebral level showing lateral displacement of nerve roots by acquired arachnoid cysts. There are bilateral metallic pedicle screws.


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Neurology_Adams. Figure 10-6. Cervical disc herniation as visualized with T2-weighted MRI. A. Parasagittal view of a large posterior disc extrusion at C6-C7. Smaller broad-based posterior disc bulges are seen at C4-C5 and C5-C6. B. Axial view of the large right posterolateral disc extrusion shown in (A) at C6-C7 (arrow) causing severe narrowing of the right neural foramen and compression of the exiting C7 nerve root. C. By way of contrast, an axial view of the broad-based posterior disc bulge at C4-C5 (arrows) causes only minimal narrowing of the spinal canal and no compression of the spinal cord.


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Neurology_Adams. Figure 10-7. Course of the brachial plexus and subclavian artery between the anterior scalene and middle scalene muscles. Dilatation of the subclavian artery just distal to the anterior scalene muscle is illustrated. Immediately distal to the anterior and middle scalene muscles is another potential area of constriction, between the clavicle and the first rib. With extension of the neck and turning of the chin to the affected side (Adson maneuver), the tension on the anterior scalene muscle is increased and the subclavian artery compressed, resulting in a supraclavicular bruit and obliteration of the radial pulse. Chapter 10 Pain in the Back, Neck, and Extremities Disorders of the Special Senses CHAPTER 11 Disorders of Smell and Taste CHAPTER 12 Disturbances of Vision CHAPTER 13 Disorders of Ocular Movement and Pupillary Function CHAPTER 14 Deafness, Dizziness, and Disorders of Equilibrium


Neurology_Adams

Neurology_Adams. The four chapters in this section are concerned with the clinical aspects of the highly specialized functions of taste and smell, vision, hearing, and the sense of balance. These special senses and the cranial nerves that subserve them represent the most finely developed parts of the sensory nervous system. Dysfunctions of the eye and ear are, of course, the domain of the ophthalmologist and otorhinolaryngologist, but they also are of great interest to the neurologist. Some defects in the special sensory apparatus reflect the presence of systemic disease and others represent the initial or leading manifestation of neurologic disease. In keeping with the general scheme of this text, the disorders of the special senses and of ocular movement are discussed in a particular sequence: first, certain facts of anatomic and physiologic importance, followed by cardinal clinical manifestations of disease, and then the syndromes of which these manifestations are a part.


Neurology_Adams

Disorders of Smell and Taste

Neurology_Adams. Disorders of Smell and Taste


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Neurology_Adams. The sensations of smell (olfaction) and taste (gustation) are suitably considered together. Physiologically, these modalities share the singular attribute of responding primarily to chemical stimuli; that is, the end organs that mediate olfaction and gustation are chemoreceptors. Also, taste and smell are interdependent clinically, as the appreciation of the flavor of food and drink depends to a large extent on its aroma, and an abnormality of one of these senses is frequently misinterpreted as an abnormality of the other. In comparison to sight and hearing, taste and smell play a less critical role in the life of the individual. However, chemical stimuli in communication between humans are probably very important for some functions that have not been fully explored. Pheromones (pherein, “to carry”; hormon, “exciting”), that is, odorants exuded from the body, as well as perfumes, play a part in sexual attraction; noxious body odors may repel. In certain vertebrates the olfactory


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Neurology_Adams. “to carry”; hormon, “exciting”), that is, odorants exuded from the body, as well as perfumes, play a part in sexual attraction; noxious body odors may repel. In certain vertebrates the olfactory system is remarkably well developed, rivaling the sensitivity of the visual system. Though humans were thought to be capable of discriminating as many as 10,000 different odorants based on work by Reed and others, recent experimental studies by Bushdid and colleagues have shown that this may be a vast underestimation.


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Neurology_Adams. Disorders of taste and smell can be persistently unpleasant, but only rarely is the loss of either of these modalities a serious handicap. Nevertheless, as all foods and inhalants pass through the mouth and nose, these two senses serve to detect noxious odors (e.g., smoke) and to avoid tainted food and potential poisons. The loss of these senses could then have serious consequences. Also, because a loss of taste and smell may signify a number of intracranial, neurodegenerative, and systemic disorders, they assume clinical importance.


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Neurology_Adams. Nerve fibers subserving the sense of smell have their cells of origin in the mucous membrane of the upper and posterior parts of the nasal cavity (superior turbinates and nasal septum). The entire olfactory mucosa covers an area of about 2.5 cm2 and contains three cell types: the olfactory receptor cells, which number between 6 and 10 million in each nasal cavity; sustentacular or supporting cells, which maintain the electrolyte (particularly potassium) levels in the extracellular milieu; and basal cells, which are stem cells and the source of both the olfactory and sustentacular cells during regeneration. The olfactory cells are actually bipolar neurons. Each of these cells has a peripheral process (the olfactory rod) from which project 10 to 30 fine hairs, or cilia. These hair-like processes, which lack motility, are the sites of olfactory receptors.


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Neurology_Adams. The central processes of these cells, or olfactory fila, are very fine (0.2 mm in diameter) unmyelinated fibers that converge to form small fascicles enwrapped by Schwann cells that pass through openings in the cribriform plate of the ethmoid bone into the olfactory bulb (Fig. 11-1). Collectively, the central processes of the olfactory receptor cells constitute the first cranial (olfactory) nerve. Notably, this is the only site in the body where neurons are in direct contact with the external environment. The epithelial surface is covered by a layer of mucus, which is secreted by tubuloalveolar cells (Bowman glands) and within which there are immunoglobulins A and M, lactoferrin, and lysoenzyme as well as odorant-binding proteins. These molecules are thought to prevent the intracranial entry of pathogens via the olfactory pathway (Kimmelman).


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Neurology_Adams. In the olfactory bulb, the receptor-cell axons synapse with granule cells and mitral cells (so-called because they are triangular, like a bishop’s miter), the dendrites of which form brush-like terminals or olfactory glomeruli (see Fig. 11-1). Smaller tufted cells in the olfactory bulb also contribute dendrites to the glomerulus. Approximately 15,000 olfactory cell axons converge on a single glomerulus. This high degree of convergence is thought to account for an integration of afferent information. The mitral and tufted cells are excitatory; the granule cells—along with centrifugal fibers from the olfactory nuclei, locus ceruleus, and piriform cortex—inhibit mitral cell activity. Presumably, interaction between these excitatory and inhibitory neurons provides the basis for the special physiologic aspects of olfaction.


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Neurology_Adams. The axons of the mitral and tufted cells form the olfactory tract, which courses along the olfactory groove of the cribriform plate to the cerebrum. Within the olfactory tract and posterior to the olfactory bulbs are groups of cells that constitute the anterior olfactory nucleus (see Fig. 11-1). Dendrites of these cells synapse with fibers of the olfactory tract, while their axons project to the olfactory nucleus and bulb of the opposite side; these neurons are thought to function as a reinforcing mechanism for olfactory impulses.


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Neurology_Adams. Posteriorly, the olfactory tract divides into medial and lateral olfactory striae. The medial stria contains fibers from the anterior olfactory nucleus; these pass to the opposite side via the anterior commissure. Fibers in the lateral stria originate in the olfactory bulb, give off collaterals to the anterior perforated substance, and terminate in the nuclei of the amygdaloid complex and the prepiriform area (also referred to as the lateral olfactory gyrus). The latter represents the primary olfactory cortex, which in humans occupies a restricted area on the anterior aspect of the parahippocampal gyrus and uncus (area 34 of Brodmann; see Figs. 21-1 and 21-2). Thus olfactory impulses reach the cerebral cortex without a relay through the thalamus; in this respect also, olfaction is unique among sensory systems. From the prepiriform cortex, fibers project to the neighboring entorhinal cortex (area 28 of Brodmann) and the medial dorsal nucleus of the thalamus; the amygdaloid nuclei


Neurology_Adams

Neurology_Adams. among sensory systems. From the prepiriform cortex, fibers project to the neighboring entorhinal cortex (area 28 of Brodmann) and the medial dorsal nucleus of the thalamus; the amygdaloid nuclei connect with the hypothalamus and septal nuclei. The role of these latter structures in olfaction is not well understood, but presumably they subserve reflexes related to eating and sexual function. As with all sensory systems, feedback regulation occurs at every point in the afferent olfactory pathway.


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Neurology_Adams. In quiet breathing, little of the air entering the nostril reaches the olfactory mucosa; sniffing carries the air into the olfactory crypt, which contains the olfactory receptors. To be perceived as an odor, an inhaled substance must be volatile—that is, spread in the air as very small particles—and soluble in water. Molecules provoking the same odor seem to be related by their shape more than by their chemical quality. When a jet of scented vapor is directed to the sensory epithelium, as by sniffing, a slow negative potential shift called the electroolfactogram (EOG) can be recorded from an electrode placed on the mucosa. The conductance changes that underlie this receptor potential are induced by molecules of odorous material dissolved in the mucus overlying the receptor.


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Neurology_Adams. The transduction of odorant stimuli to electrical signals is mediated in part by a guanosine triphosphate (GTP)-dependent adenylyl cyclase (“G protein”). Like other cyclic adenosine monophosphate (AMP) pathways, this one utilizes the same intracellular second messenger, which opens a voltage-gated calcium channel in the receptor. There follow conformational changes in transmembrane receptor proteins and a series of intracellular biochemical events that generate axon potentials.


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Neurology_Adams. Intensity of olfactory sensation is determined by the frequency of firing of afferent neurons. The quality of the odor is thought to be provided by “cross-fiber” activation and integration, as described earlier, because the individual receptor cells are responsive to a wide variety of odorants and exhibit different types of responses to stimulants—excitatory, inhibitory, and on–off responses have been obtained. The olfactory potential can be eliminated by destroying the olfactory receptor surface or the olfactory filaments. The loss of EOG occurs 8 to 16 days after severance of the nerve; the receptor cells disappear, but the sustentacular (Sertoli) cells are not altered. As a result of division of the basal cells of the olfactory epithelium, the olfactory receptor cells are constantly dying and being replaced by new ones. In this respect, the chemoreceptors, both for smell and for taste, constitute one of the few examples of neuronal regeneration in humans.


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Neurology_Adams. The trigeminal system also participates in chemesthesis through undifferentiated receptors in the nasal mucosa. These receptors have little discriminatory ability but a great sensitivity to irritant stimuli. The trigeminal afferents also release neuropeptides that result in hypersecretion of mucus, local edema, and sneezing. Finally, stimulation of the olfactory pathway at cortical sites of the temporal lobe may also induce olfactory experiences.


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Neurology_Adams. The olfactory system adapts quickly to a sensory stimulus, and for sensation to be sustained, there must be repeated stimulation. The olfactory sense differs from other senses in yet another way. It is common experience that an aroma can restore long-forgotten memories of complex experiences. That olfactory and emotional stimuli are strongly linked is not surprising in view of their common roots in the limbic system. Yet, paradoxically, the ability to recall an odor is negligible in comparison with the ability to recall sounds and sights. As Vladimir Nabokov has remarked, “Memory can restore to life everything except smells.” It is also interesting that dreams do not embody olfactory experiences.


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Neurology_Adams. The remarkable evolutionary role of olfactory receptors can be appreciated by the fact that about 2 percent of the human genome exists to express unique odorant receptors (over 400 distinct functional genes). The wide diversity of these transmembrane proteins permits subtle differentiation of thousands of different odorant molecules, as delineated by Young and Trask and the genetic basis for which Buck and Axel were awarded a Nobel Prize. This specificity for molecules is encoded neuroanatomically. Different odorant molecules activate specific olfactory receptors. Each olfactory neuron expresses only one allele of one receptor gene. Moreover, each olfactory glomerulus receives inputs from neurons expressing only one type of odorant receptor. In this way, each of the glomeruli is attuned to a distinct type of odorant stimulus. Presumably, this encoding is preserved in the olfactory cortex.


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Neurology_Adams. Something is to be learned from a second, distinct olfactory system in many animals (the vomeronasal olfactory system or organ of Jacobson), in which the repertoire of olfactory receptors is much more limited than in their main olfactory system. This functionally and anatomically distinct olfactory tissue is attuned to pheromones and thereby importantly influences menstrual, reproductive, ingestive, and defensive behavior (see review of Wysocki and Meredith). The vomeronasal receptors employ different signaling mechanisms than other olfactory receptors and project to the hypothalamus and amygdala via a distinct accessory olfactory bulb. Clinical Manifestations of Olfactory Lesions


Neurology_Adams

Neurology_Adams. Clinical Manifestations of Olfactory Lesions Disturbances of olfaction may be subdivided into four groups, as follows: 1. Quantitative abnormalities: loss or reduction of the sense of smell (anosmia, hyposmia) or, rarely, increased olfactory acuity (hyperosmia) 2. Qualitative abnormalities: distortions or illusions of smell (dysosmia or parosmia) 3. Olfactory hallucinations and delusions caused by temporal lobe disorders or psychiatric disease 4. Higher-order loss of olfactory discrimination (olfactory agnosia) Anosmia, or Loss of the Sense of Smell (Table 11-1) This is the most frequent clinical abnormality of olfaction and, if unilateral, usually is not recognized by the patient. Unilateral anosmia can sometimes be demonstrated in the hysterical patient on the side of anesthesia, blindness, or deafness. Bilateral anosmia, on the other hand, is a common complaint, and the patient is usually convinced that the sense of taste has been lost as well (ageusia).


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Neurology_Adams. This calls attention to the fact that taste depends largely on the volatile particles in foods and beverages, which reach the olfactory receptors through the nasopharynx, and that the perception of flavor is a combination of smell, taste, and tactile sensation. This can be proved by demonstrating that patients with anosmia but without a complaint of ageusia are able to distinguish the elementary taste sensations on the tongue (sweet, sour, bitter, and salty). The olfactory defect can be verified readily enough by presenting a series of nonirritating olfactory stimuli (vanilla, peanut butter, coffee, tobacco) and asking the patient to sniff once and identify them. If the odors can be detected and described, even if they cannot be named, it may be assumed that the olfactory nerves are relatively intact (humans can distinguish many more odors than they can identify by name). If they cannot be detected, there is an olfactory defect. Ammonia and similar pungent substances are unsuitable


Neurology_Adams

Neurology_Adams. intact (humans can distinguish many more odors than they can identify by name). If they cannot be detected, there is an olfactory defect. Ammonia and similar pungent substances are unsuitable stimuli because they do not test the sense of smell but have a primary irritating effect on the mucosal-free nerve endings of the trigeminal nerves.


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Neurology_Adams. The value of testing smell in one nostril at a time has been questioned, for example by Welge-Luessen and colleagues, who studied olfactory groove meningiomas. They found, contrary to expectations, that this test was not sensitive to the presence of a unilateral lesion, ostensibly because of mixing of air in the nasopharynx as well as crossing of medial olfactory stria fibers as described earlier. Nonetheless, other experience suggests that rapidly sniffing through one nostril does briefly allow segregation of each side of the nasal cavities and can detect unilateral lesions.


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Neurology_Adams. A more elaborate scratch-and-sniff test has been developed and standardized by Doty and colleagues (University of Pennsylvania Smell Identification Test). In this test the patient attempts to identify 40 microencapsulated odorants, and olfactory performance is compared with that of ageand sex-matched normal individuals. Unique features of this test are a means for detecting malingering and amenability to self-administration. Air-dilution olfactory detection is an even more refined way of determining thresholds of sensation and of demonstrating normal olfactory perception in the absence of odor identification. The use of olfactory evoked potentials is being investigated in some electrophysiology laboratories, but their reliability is uncertain. These last two refined techniques are essentially research tools and are not used in neurologic practice.


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Neurology_Adams. The loss of smell usually falls into one of three categories: nasal (in which odorants do not reach the olfactory receptors), olfactory neuroepithelial (caused by destruction of receptors or their axon filaments), and central (olfactory pathway lesions). Viewed from another perspective, in an analysis of 4,000 cases of anosmia from specialized clinics, Hendriks found that the three most common diagnoses were viral infection of the upper respiratory tracts (the largest group), nasal or paranasal sinus disease, and head injury.


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Neurology_Adams. Regarding the nasal diseases responsible for bilateral hyposmia or anosmia, the most frequent are those in which hypertrophy and hyperemia of the nasal mucosa prevent olfactory stimuli from reaching the receptor cells. Heavy smoking is the most frequent cause of this type of hyposmia in practice. Chronic atrophic rhinitis; sinusitis of allergic, vasomotor, or infective types; nasal polyposis; and overuse of topical vasoconstrictors are other common causes. Biopsies of the olfactory mucosa in cases of allergic rhinitis have shown that the sensory epithelial cells are still present, but their cilia are deformed and shortened and are buried under other mucosal cells. Influenza, herpes simplex, and hepatitis virus infections may be followed by hyposmia or anosmia caused by destruction of receptor cells; if the basal cells are also destroyed, this may be permanent. These cells may also be affected as a result of atrophic rhinitis and local radiation therapy or by a rare type of tumor


Neurology_Adams

Neurology_Adams. receptor cells; if the basal cells are also destroyed, this may be permanent. These cells may also be affected as a result of atrophic rhinitis and local radiation therapy or by a rare type of tumor (esthesioneuroblastoma) that originates in the olfactory epithelium. There is also a group of uncommon diseases in which the primary receptor neurons are congenitally absent or hypoplastic and lack cilia. One of these is the Kallmann syndrome of congenital anosmia and hypogonadotropic hypogonadism. A similar disorder occurs in Turner syndrome and in albinism because of an ill-defined congenital structural defect.


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Neurology_Adams. Anosmia that follows head injury is most often a result of tearing of the delicate filaments of the receptor cells as they pass through the cribriform plate, especially if the injury is severe enough to cause fracture. The damage may be unilateral or bilateral. With closed head injury, complete anosmia is relatively infrequent (6 percent of Sumner’s series of 584 cases), but lesser degrees are common in our experience. Some recovery of olfaction occurs in about one-third of cases over a period of several days to months. Beyond 6 to 12 months, recovery is negligible. Cranial surgery, subarachnoid hemorrhage, and chronic meningeal inflammation may have similar effects.


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Neurology_Adams. In some of the cases of traumatic anosmia, there is also a loss of taste (ageusia). Ferrier, who first described traumatic ageusia in 1876, noted that there was always anosmia as well—an observation subsequently corroborated by Sumner. Often, the ageusia also clears within a few weeks. A bilateral traumatic lesion near the frontal operculum and paralimbic region, where olfactory and gustatory receptive zones are in close proximity, would best explain this concurrence, but this has not been proven. As stated earlier, the interruption of olfactory filaments alone would explain a reduction in the ability to perceive the subtleties of specific flavors, but does not explain ageusia.


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Neurology_Adams. Olfactory acuity varies throughout the menstrual cycle, possibly through a imputed vomeronasal system in humans, and may be disordered during pregnancy as well. Nutritional and metabolic disorders such as thiamine deficiency (Wernicke disease), vitamin A deficiency, adrenal and perhaps thyroid insufficiency, cirrhosis, and chronic renal failure may give rise to anosmia, all as a result of sensorineural dysfunction. A large number of toxic agents—the more common ones being organic solvents (benzene), metals including platinum-containing chemotherapies, dusts, cocaine, corticosteroids, methotrexate, aminoglycoside antibiotics, tetracyclines, opiates, and l-dopa—can damage the olfactory epithelium (Doty et al). Alcoholics with Korsakoff psychosis also have a defect in odor discrimination (Mair et al). In this disorder, anosmia is presumably caused by degeneration of neurons in the higher-order olfactory systems involving the medial thalamic nuclei.


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Neurology_Adams. Anosmia has been found in some patients with temporal lobe epilepsy and particularly in such patients who had been subjected to anterior temporal lobectomy. In these conditions, Andy and coworkers have found impairment in discriminating the quality of odors and in matching odors with test objects seen or felt. As with other sensory modalities, olfaction (and taste) is diminished with aging (presbyosmia). The receptor cell population is depleted, and if the loss is regional, neuroepithelium is slowly replaced with respiratory epithelium (which is normally present in the nasal cavity and serves to filter, humidify, and warm incoming air). Neurons of the olfactory bulb may also be reduced as part of the aging process.


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Neurology_Adams. Bilateral anosmia has been a manifestation of malingering, now that it has been recognized as a compensable disability. The fact that true anosmics will complain inordinately of a loss of taste (but show normal taste sensation) may help to separate them from malingerers. If it were to be perfected, testing of olfactory evoked potentials would be of use here.


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Neurology_Adams. The nasal epithelium or the olfactory nerves themselves may be affected in Wegener granulomatosis and by craniopharyngioma, respectively. A meningioma of the olfactory groove may implicate the olfactory bulb and tract and may extend posteriorly to involve the optic nerve, sometimes with optic atrophy; if combined with papilledema on the opposite side, these abnormalities are known as the Foster Kennedy syndrome (see Chap. 12). A large aneurysm of the anterior cerebral or anterior communicating artery may produce a similar constellation. With tumors confined to one side, the anosmia may be strictly unilateral, in which case it will not be reported by the patient but will be found on examination. The limitations of testing each side of the nose separately have been mentioned earlier. These defects in the sense of smell are attributable to lesions of either the receptor cells and their axons or the olfactory bulbs, and current test methods do not distinguish between lesions in these two


Neurology_Adams

Neurology_Adams. defects in the sense of smell are attributable to lesions of either the receptor cells and their axons or the olfactory bulbs, and current test methods do not distinguish between lesions in these two localities. In some cases of increased intracranial pressure, olfactory sense has been impaired without evidence of lesions in the olfactory bulbs.


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Neurology_Adams. The term specific anosmia has been applied to an unusual olfactory phenomenon in which a person with normal olfactory acuity for most substances encounters a particular compound or class of compounds that is odorless to him, although obvious to others. In a sense, this is a condition of “smell blindness,” analogous to color blindness. The basis of this disorder is unclear although there is evidence that specific anosmia for musky and uriniferous odors is inherited as an autosomal recessive trait (see Amoore).


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Neurology_Adams. Whether a true hyperosmia exists is a matter of conjecture, but it is so frequently reported by migraineurs that the problem seems worthy of attention. Anxious, highly introspective individuals may complain of being unduly sensitive to odors, but for the most part there is no proof of an actual change in their threshold of perception of odors. Interestingly, Menashe and colleagues have linked enhanced sensitivity to the odorant isovaleric acid to single nucleotide polymorphism (SNP) variants of the olfactory receptor gene OR11H7P, and more associations of this kind may be elucidated.


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Neurology_Adams. Olfaction in neurodegenerative disease Hyman and colleagues have emphasized the many earlier observations of an early neuronal degeneration in the olfactory region of the hippocampus in cases of Alzheimer, Lewy body, and Parkinson disease. Moreover, a large proportion of patients with other degenerative diseases of the brain have anosmia or hyposmia. A number of theories have been proposed to explain the initial loss of smell, the most relevant of which is based on the finding that the earliest neuropathologic changes of many neurodegenerative processes begin in olfactory structures and then appears serially in neighboring structures, only later reaching the parts of the brain that produce the characteristic neurologic features of these diseases. The implication from these findings, originating with Braak and Braak, has been that Lewy bodies in particular are caused by a pathogen that enters through the peripheral olfactory system and proceeds centrally through the medial temporal


Neurology_Adams

Neurology_Adams. with Braak and Braak, has been that Lewy bodies in particular are caused by a pathogen that enters through the peripheral olfactory system and proceeds centrally through the medial temporal lobe (see Chap. 38 for further details). Prions have been suggested as a candidate agent because of their ability to alter protein folding and to transfer this property in a sequentially topographic manner. The studies relating to olfaction in Parkinson disease have been reviewed by Doty, Braak and colleagues, Quinn et al, and Benarroch. It should be emphasized to patients, however, that the reverse is not the case; that is, the majority of individuals with hyposmia do not have a generalized neurodegenerative disease.


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Neurology_Adams. These terms refer to distortions of odor perception where an odor is present. Parosmia may occur with local nasopharyngeal conditions such as infection of the nasal sinuses and upper respiratory infections. In some instances, the abnormal tissue itself may be the source of unpleasant odors; in others, where partial injuries of the olfactory bulbs have occurred, parosmia is in the nature of an olfactory illusion. Parosmia may also be a troublesome symptom in persons with depressive and psychotic illnesses, who may report that every article of food has an extremely unpleasant odor (cacosmia). Sensations of disagreeable taste are often associated (cacogeusia). Nothing is known of the basis of this state; there is usually no loss of discriminative sensation.


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Neurology_Adams. The treatment of parosmia is difficult. The use of neuroleptic or antiepileptic drugs has yielded unpredictable results. Claims for the efficacy of zinc and vitamins have not been verified (and there is a risk that zinc administration may interfere with the absorption of copper). Some reports indicate that repeated anesthetization of the nasal mucosa reduces or abolishes the parosmic disturbance. In many cases, the disorder subsides spontaneously. Minor degrees of parosmia are not necessarily abnormal, for unpleasant odors have a way of lingering for several hours and of being reawakened by other olfactory stimuli, as every pathologist knows.


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Neurology_Adams. The report of an odor without stimulus, olfactory hallucination, is always of central origin. The patient perceives an odor that no one else can detect (phantosmia). Most often this a manifestation of temporal lobe seizures (“uncinate fits”), in which circumstances the olfactory hallucinations are brief and accompanied or followed by an alteration of consciousness and other manifestations of epilepsy (see Chap. 15 on epilepsy).


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Neurology_Adams. If the patient is convinced of the presence of what is in fact a hallucination and also gives it personal origin, the symptom assumes the status of a delusion (a fixed false belief). The combination of olfactory hallucinations and delusions of this type signifies a psychiatric illness. Zilstorff wrote informatively on this subject. There is often a complaint of a large array of odors, most of them noxious and seemingly emanating from the patient (intrinsic hallucinations); in others, they are attributed to an external source (extrinsic hallucinations). Both types vary in intensity and are remarkable with respect to their persistence. They may be combined with gustatory hallucinations. According to Pryse-Phillips, who took note of the psychiatric illness in a series of 137 patients with olfactory hallucinations, most were associated with endogenous depression or schizophrenia. In schizophrenia, the olfactory stimulus is usually interpreted as arising externally, and as being induced by


Neurology_Adams

Neurology_Adams. hallucinations, most were associated with endogenous depression or schizophrenia. In schizophrenia, the olfactory stimulus is usually interpreted as arising externally, and as being induced by someone for the purpose of upsetting the patient. In depression, the perception is of the stimulus being intrinsic. The patient may go to great lengths to rid himself of the perceived odor, the usual ones being excessive washing and use of deodorants; the condition may lead to social withdrawal. There is reason to believe that the amygdaloid group of nuclei is the source of the hallucinations, as stereotactic lesions here have reportedly ameliorated both the olfactory hallucinations and the psychiatric disorder (see Chitanondh).


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Neurology_Adams. Olfactory hallucinations and delusions may occur in conjunction with Alzheimer dementia, but one should also consider the possibility of a late-life depression. Loss of Olfactory Discrimination (Olfactory Agnosia) Finally, one must consider a disorder in which the primary perceptual aspects of olfaction (detection of odors, adaptation to odors, and recognition of different intensities of the same odor) are intact, but the capacity to distinguish between odors and their recognition by quality is impaired or lost. In the writings on this subject, this deficit is usually referred to as a disorder of olfactory discrimination. In dealing with other sense modalities, however, the inability to identify and name a perceived sensation would be called an agnosia. To recognize this deficit requires special testing, such as matching to sample, the identification and naming of a variety of scents, and determining whether two odors are identical or different.


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Neurology_Adams. Such an alteration of olfactory function has been shown to characterize patients with the alcoholic form of Korsakoff psychosis; this impairment is not attributable to reduced olfactory acuity or to failure of learning and memory (Mair et al). As indicated previously, the olfactory disorder in the alcoholic Korsakoff patient is most likely caused by lesions in the medial dorsal nucleus of the thalamus; several observations in animals indicate that this nucleus and its connections with the orbitofrontal cortex give rise to deficits in odor discrimination (Mair et al, Slotnick and Kaneko). Eichenbaum and associates demonstrated a similar impairment of olfactory capacities in a patient who had undergone extensive bilateral medial temporal lobe resections. The operation was believed to have eliminated a substantial portion of the olfactory afferents to the frontal cortex and thalamus, although there was no anatomic verification of this. In patients with stereotactic or surgical


Neurology_Adams

Neurology_Adams. to have eliminated a substantial portion of the olfactory afferents to the frontal cortex and thalamus, although there was no anatomic verification of this. In patients with stereotactic or surgical amygdalotomies, Andy and coworkers noted a similar reduction in odor discrimination. Thus it appears that both portions of the higher olfactory pathways (medial temporal lobes, and medial dorsal nuclei) are necessary for the discrimination and identification of odors.


Neurology_Adams

Neurology_Adams. The sensory receptors for taste (taste buds) are distributed over the surface of the tongue and, in smaller numbers, over the soft palate, pharynx, larynx, and esophagus. Mainly they are located in the epithelium along the lateral surfaces of the circumvallate and foliate papillae and to a lesser extent on the surface of the fungiform papillae. The taste buds are round or oval structures, each composed of up to 200 vertically oriented receptor cells arranged like the staves of a barrel. The superficial portion of the bud is marked by a small opening, the taste pore or pit, which opens onto the mucosal surface. The tips of the sensory cells project through the pore as a number of filiform microvilli (“taste hairs”). Fine, unmyelinated sensory fibers penetrate the base of the taste bud and synapse directly with the sensory taste cells, which have no axons.


Neurology_Adams

Neurology_Adams. The taste receptors are activated by chemical substances in solution and transmit their activity along the sensory nerves to the brainstem. There are four primary and readily tested taste sensations that have been long known: salty, sweet, bitter, and sour; recently a fifth, umami, signifying a savory taste—the taste of glutamate, aspartate, and certain ribonucleotides—has been added. The full range of taste sensations is much broader, consisting of combinations of these elementary gustatory sensations. Older notions of a “tongue map,” which implied the existence of specific areas subserving one or another taste, are incorrect. Any one taste receptor is capable of responding to a number of sapid substances but each is preferentially sensitive to one substance. In other words, the receptors are only relatively specific. The sensitivity of these receptors is remarkable: as little as 0.05 mg/dL of quinine sulfate will arouse a bitter taste when applied to the base of the tongue.


Neurology_Adams

Neurology_Adams. A G-protein transduction system (gustducin), similar to the one for olfaction, has been found to be operative in signaling taste sensations in the tongue receptors. A discussion of this system can be found in the commentary by Brand.


Neurology_Adams

Neurology_Adams. The receptor cells of the taste buds have a brief life cycle (about 10 days), being replaced constantly by mitotic division of adjacent basal epithelial cells. The number of taste buds, not large to begin with (approximately 10,000), is gradually reduced with age; also, changes occur in the taste cell membranes, with impaired function of ion channels and receptors (Mistretta). Gustatory (and olfactory) acuity diminishes with age (everything begins to taste and smell the same). According to Schiffman, taste thresholds for salt, sweeteners, and amino acids are 2 to 2.5 times higher in the elderly than in the young. The reduction in the acuity of taste and smell with aging may lead to a distortion of food habits (e.g., excessive use of salt and other condiments) and contribute to the anorexia and weight loss of elderly persons.


Neurology_Adams

Neurology_Adams. Richter has explored the biologic role of taste in normal nutrition. Animals made deficient in sodium, calcium, certain vitamins, proteins, etc., will automatically select the correct foods, on the basis of their taste, to compensate for their deficiency. Interesting genetic polymorphisms in the receptor for sweet substances in rats have been found to underlie differences in the proclivity to ingest sweet substances, and a similar system has been proposed in humans (Chaudhari and Kinnamon). Neural Innervation of the Tongue


Neurology_Adams

Neurology_Adams. Neural Innervation of the Tongue Sensory impulses for taste arise from several sites in the oropharynx and are transmitted to the medulla via several cranial nerves (V, VII, IX, and X). The main pathway arises on the anterior two-thirds of the tongue; these taste fibers first run in the lingual nerve (a major branch of the mandibular segment of the trigeminal [V] cranial nerve). After coursing within the lingual nerve for a short distance, the taste fibers diverge to enter the chorda tympani (a branch of the facial [VII] nerve); thence they pass through the pars intermedia and geniculate ganglion of the seventh nerve to the rostral part of the nucleus of the tractus solitarius in the posterolateral medulla, where all taste afferents converge (see the following text and Fig. 44-3).


Neurology_Adams

Neurology_Adams. From the posterior one-third of the tongue, soft palate, and palatal arches, the sensory taste fibers are conveyed via the glossopharyngeal (IX) nerve and ganglion nodosum to the nucleus of the tractus solitarius. Taste fibers from the extreme dorsal part of the tongue and the few that arise from taste buds on the pharynx and larynx run in the vagus (X) nerve. The gustatory nucleus is situated in the rostral and lateral parts of the nucleus tractus solitarius, which receive the special afferent (taste) fibers from the facial and glossopharyngeal nerves. Probably both sides of the tongue are represented in this nucleus.


Neurology_Adams

Neurology_Adams. Fibers from the palatal taste buds pass through the pterygopalatine ganglion and adjacent to greater superficial petrosal nerve fibers, joining the facial nerve at the level of the geniculate ganglion, and proceed to the nucleus of the tractus solitarius (see Fig. 44-3). Possibly, some taste fibers from the tongue may also reach the brainstem via the mandibular division of the trigeminal nerve. The presence of this alternative pathway probably accounts for reported instances of unilateral taste loss that have followed section of the root of the trigeminal nerve and instances in which no loss of taste has occurred with section of the chorda tympani.


Neurology_Adams

Neurology_Adams. The second sensory neuron for taste has been difficult to identify. Neurons from the gustatory segment of the nucleus solitarius project to adjacent nuclei (e.g., dorsal motor nucleus of the vagus, ambiguus, salivatorius superior and inferior, trigeminal, and facial nerves), which serve viscerovisceral and viscerosomatic reflex functions, but those concerned with the conscious recognition of taste are currently considered to form an ascending pathway to a pontine parabrachial nucleus. From the latter, two ascending pathways have been traced (in animals). One is the solitariothalamic lemniscus to the ventroposteromedial nucleus of the thalamus. A second passes to the ventral parts of the forebrain, to parts of the hypothalamus (which probably influences autonomic function), and to other basal forebrain limbic areas in or near the uncus of the temporal lobe. Other ascending fibers lie near the medial lemniscus and are both crossed and uncrossed. Experiments in animals indicate that


Neurology_Adams

Neurology_Adams. basal forebrain limbic areas in or near the uncus of the temporal lobe. Other ascending fibers lie near the medial lemniscus and are both crossed and uncrossed. Experiments in animals indicate that taste impulses from the thalamus project to the tongue–face area of the postrolandic sensory cortex. This is probably the end station of gustatory projections in humans as well, insofar as gustatory hallucinations have been produced by electrical stimulation of the parietal and/or rolandic opercula (Hausser-Hauw and Bancaud). Penfield and Faulk evoked distinct taste sensations by stimulating the anterior insula.


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Neurology_Adams. Clinical Manifestations of Disorders of Taste Testing of Taste Sensation


Neurology_Adams

Neurology_Adams. Unilateral gustatory impairment can be identified by withdrawing the tongue with a gauze sponge and using a moistened applicator to place a few crystals of salt, sugar, lemon (sour), and quinine (bitter) on discrete parts of the tongue; the tongue is then wiped clean and the subject is asked to report what was sensed. One use of such testing is to corroborate the existence of Bell palsy by comparing taste sensation on each side of the anterior tongue (see Chap. 44). A stimulus that has been used as a surrogate for sour sensation is a low-voltage direct current, the electrodes of which can be accurately placed on the tongue surface. If the taste loss is bilateral, mouthwashes with a dilute solution of sucrose, sodium chloride, citric acid, and quinine may be used. After swishing, the test fluid is spit out and the mouth rinsed with water. The patient indicates whether a taste was detected and then is asked to try to identify it. Special types of apparatus (electrogustometers) have been


Neurology_Adams

Neurology_Adams. is spit out and the mouth rinsed with water. The patient indicates whether a taste was detected and then is asked to try to identify it. Special types of apparatus (electrogustometers) have been devised for the measurement of taste intensity and for determining the detection and recognition thresholds of taste and olfactory stimuli (Krarup; Henkin et al), but these are beyond the needs of the usual clinical examination.


Neurology_Adams

Neurology_Adams. Ageusia, or Loss of the Sense of Taste (Table 11-2)


Neurology_Adams

Neurology_Adams. Apart from the loss of taste sensation that accompanies normal aging, smoking is probably the most common cause of impairment of taste sensation. Extreme drying of the tongue from any cause may lead to temporary loss or reduction of the sense of taste (ageusia or hypogeusia), as saliva is essential for normal taste function. Saliva acts as a solvent for chemical substances in food and for conveying them to taste receptors. Dryness of the mouth (xerostomia) from inadequate saliva, as occurs in Sjögren syndrome; hyperviscosity of saliva, as in cystic fibrosis; irradiation of head and neck; and pandysautonomia all interfere with taste. Also, in familial dysautonomia (Riley-Day syndrome), the number of circumvallate and fungiform papillae is reduced, accounting for a diminished ability to taste sweet and salty foods. If unilateral, ageusia is seldom the source of complaint. Taste is frequently lost over the anterior two-thirds of one side of the tongue in cases of mundane Bell palsy, as


Neurology_Adams

Neurology_Adams. sweet and salty foods. If unilateral, ageusia is seldom the source of complaint. Taste is frequently lost over the anterior two-thirds of one side of the tongue in cases of mundane Bell palsy, as indicated previously and in Chap. 44.


Neurology_Adams

Neurology_Adams. A permanent decrease in the acuity of taste and smell (hypogeusia and hyposmia), sometimes associated with perversions of these sensory functions (dysgeusia and dysosmia), may follow influenza-like illnesses. These abnormalities have been associated with pathologic changes in the taste buds as well as in the nasal mucous membranes. In a group of 143 patients who presented with hypogeusia and hyposmia, 87 were of this postinfluenza type, as determined by Henkin and colleagues; the remainder developed their symptoms in association with scleroderma, acute hepatitis, viral encephalitis, myxedema, adrenal insufficiency, malignancy, deficiency of vitamins B and A, and the administration of a wide variety of drugs. Also, according to Schiffman, more than 250 drugs have been implicated in the alteration of taste sensation, making it necessary to consider virtually all drugs as a cause of taste loss. Lipid-lowering drugs, antihistamines, antimicrobials, antineoplastics, bronchodilators,


Neurology_Adams

Neurology_Adams. alteration of taste sensation, making it necessary to consider virtually all drugs as a cause of taste loss. Lipid-lowering drugs, antihistamines, antimicrobials, antineoplastics, bronchodilators, antidepressants, and antiepileptics are the main offenders, but little is known about the mechanisms by which drugs induce these effects. More obvious is altered taste because of nasally and orally administered inhalant drugs, including the “triptans” for migraine and a variety of antiallergy and antiasthmatic medications.


Neurology_Adams

Neurology_Adams. Distortions of taste and loss of taste are sources of complaint in patients with certain local malignant tumors. Oropharyngeal tumors may, of course, abolish taste by invading the chorda tympani and lingual nerves or the skull base foramina through which these nerves pass. Malnutrition because of neoplasm or radiation therapy may also cause ageusia. Some patients with certain cancers remark on a reduced perception for bitter foods, and some who have been radiated for breast cancer or sublingual or oropharyngeal tumors find sour foods intolerable. The loss of taste from radiation of the oropharynx is usually recovered within a few weeks or months; the reduced turnover of taste buds caused by radiation therapy usually recovers.


Neurology_Adams

Neurology_Adams. An interesting syndrome of idiopathic hypogeusia—in which decreased taste acuity is associated with dysgeusia, hyposmia, and dysosmia—has been described by Henkin, Schechter and colleagues. Food has an unpleasant taste and aroma, to the point of being revolting (cacogeusia and cacosmia); the persistence of these symptoms may lead to a loss of weight, anxiety, and depression. Unilateral lesions of the medulla oblongata have not been reported to cause ageusia, perhaps because the nucleus of the tractus solitarius is outside the zone of infarction or because there is representation from both sides of the tongue in each nucleus. Unilateral thalamic and parietal lobe lesions, however, have both been associated with contralateral impairment of taste sensation in rare cases.


Neurology_Adams

Neurology_Adams. As indicated previously, a gustatory aura occasionally marks the beginning of a seizure originating in the frontoparietal (supra-sylvian) cortex or in the uncal region. Gustatory hallucinations are much less frequent than olfactory ones. Nevertheless, gustatory sensations were reported in 30 of 718 cases of intractable epilepsy (Hausser-Hauw and Bancaud). During surgery, these investigators produced an aura of disagreeable taste by electrical stimulation of the parietal and frontal opercula, and also by stimulation of the hippocampus and amygdala (uncinate seizures). In their view, the low-threshold seizure focus for taste in the temporal lobe is secondary to functional disorganization of the opercular gustatory cortex by the seizure. Gustatory hallucinations were more frequent with right hemisphere lesions, and in half of the cases the gustatory aura was followed by a convulsion.


Neurology_Adams

Neurology_Adams. Zinc supplements are contained in over-the-counter and complementary medical products aimed at improving smell and appetite and for the treatment of incipient colds. We have had no opportunity to confirm the often-cited benefits of zinc on any of these conditions, and the supporting evidence is sparse; however, the continued administration of zinc in high doses has been associated with the development of copper deficiency and a myeloneuropathy (see Chaps. 38 and 42).


Neurology_Adams

Neurology_Adams. Burning mouth syndrome Another poorly defined disorder is the burning mouth syndrome, which occurs mainly in postmenopausal women and is characterized by persistent, severe intraoral pain (particularly of the tongue). We have seen what we believe to be fragmentary forms of the syndrome in which pain and burning are isolated to the alveolar ridge or gingival mucosa. The oral mucosa appears normal and some patients may report a diminution of taste sensation. A small number of such patients prove to have diabetes, Sjögren syndrome, or vitamins B2 or B12 deficiency (causing glossitis), but in most no systemic illness or local abnormality can be found. Many such patients that we have encountered appeared to have a depressive illness, but they responded only inconsistently to administration of antidepressants. A few patients have this oral complaint as a component of a small fiber neuropathy or ganglionopathy (see Chap. 43). Clonazepam may be useful, and capsaicin has been tried with


Neurology_Adams

Neurology_Adams. of antidepressants. A few patients have this oral complaint as a component of a small fiber neuropathy or ganglionopathy (see Chap. 43). Clonazepam may be useful, and capsaicin has been tried with uncertain results. This disorder and others in which burning is a prominent feature is commented on in Chap. 7.


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Neurology_Adams. Amoore JE: Specific anosmias. In: Getchell TV, Bartoshuk LM, Doty RL, Snow JB (eds): Smell and Taste in Health and Disease. New York, Raven Press, 1991, pp 655–664. Andy OJ, Jurko MF, Hughes JR: The amygdala in relation to olfaction. Confin Neurol 37:215, 1975. Benarroch EE: Olfactory system. Functional organization and involvement in neurodegenerative disease. Neurology 75:1104, 2010. Braak H, Ghebremedhin E, Rub U, et al: Stages of development of Parkinson’s disease-related pathology. Cell Tissue Res 318:121, 2004. Brand JG: Within reach of an end to unnecessary bitterness. Lancet 356:1371, 2000. Buck LB: Smell and taste: The chemical senses. In: Kandel ER, Schwartz JH, Jessel TM (eds): Principles of Neural Science, 4th ed. New York, McGraw-Hill, 2000, pp 625–647. Bushdid C, Magnasco MO, Bosshall LB, Keller A: Humans can discriminate more than 1 trillion olfactory stimuli. Science 343:1370, 2014.


Neurology_Adams

Neurology_Adams. Bushdid C, Magnasco MO, Bosshall LB, Keller A: Humans can discriminate more than 1 trillion olfactory stimuli. Science 343:1370, 2014. Chaudhari N, Kinnamon SC: Molecular basis of the sweet tooth? Lancet 358:210, 2001. Chitanondh H: Stereotaxic amygdalotomy in the treatment of olfactory seizures and psychiatric disorders with olfactory hallucinations. Confin Neurol 27:181, 1966. Doty RL: Olfactory dysfunction in neurodegenerative disorders. In: Getchell TV, Bartoshuk LM, Doty RL, Snow JB (eds): Smell and Taste in Health and Disease. New York, Raven Press, 1991, pp 735–751. Doty RL, Shaman P, Applebaum SL: Smell identification ability: changes with age. Science 226:1441, 1984. Doty RL, Shaman P, Dann M: Development of University of Pennsylvania Smell Identification Test. Physiol Behav 32:489, 1984. Eichenbaum H, Morton TH, Potter H, Corkin S: Selective olfactory deficits in case H.M. Brain 106:459, 1983.


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Neurology_Adams. Eichenbaum H, Morton TH, Potter H, Corkin S: Selective olfactory deficits in case H.M. Brain 106:459, 1983. Hausser-Hauw C, Bancaud J: Gustatory hallucinations in epileptic seizures. Brain 110:339, 1987. Hendriks AP: Olfactory dysfunction. Rhinology 4:229, 1988. Henkin RI, Gill JR Jr, Bartter FC: Studies on taste thresholds in normal man and in patients with adrenal cortical insufficiency: The effect of adrenocorticosteroids. J Clin Invest 42:727, 1963. Henkin RI, Larson AL, Powell RD: Hypogeusia, dysgeusia, hyposmia and dysosmia following influenza-like infection. Ann Otol Rhinol Laryngol 84:672, 1975. Henkin RI, Schechter PJ, Hoye R, Mattern CFT: Idiopathic hypogeusia with dysgeusia, hyposmia, and dysosmia: a new syndrome. JAMA 217:434, 1971. Hyman BT, van Hoesen GW, Damasio AR: Alzheimer disease: cell specific pathology isolates the hippocampal formation. Science 225:1168, 1984. Kimmelman CP: Clinical review of olfaction. Am J Otolaryngol 14:227, 1993.


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Neurology_Adams. Kimmelman CP: Clinical review of olfaction. Am J Otolaryngol 14:227, 1993. Krarup B: Electrogustometry: a method for clinical taste examinations. Acta Otolaryngol 69:294, 1958. Mair R, Capra C, McEntee WJ, Engen T: Odor discrimination and memory in Korsakoff’s psychosis. J Exp Psychol 6:445, 1980. Menashe I, Abaffy T, Hasin Y, et al: Genetic elucidation of human hyperosmia to isovaleric acid. PLOS Biology 5:2462, 2007. Mistretta CM: Aging effects on anatomy and neurophysiology of taste and smell. Gerontology 3:131, 1984. Penfield W, Faulk ME: The insula: further observations on its function. Brain 78:445, 1955. Pryse-Phillips W: Disturbances in the sense of smell in psychiatric patients. Proc R Soc Med 68:26, 1975. Quinn NP, Rossor MN, Marsden CD: Olfactory threshold in Parkinson’s disease. J Neurol Neurosurg Psychiatry 50:88, 1987. Reed RR: The molecular basis of sensitivity and specificity in olfaction. Semin Cell Biol 5:33, 1994.


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Neurology_Adams. Parkinson’s disease. J Neurol Neurosurg Psychiatry 50:88, 1987. Reed RR: The molecular basis of sensitivity and specificity in olfaction. Semin Cell Biol 5:33, 1994. Richter CP: Total self-regulatory functions in animals and human beings. Harvey Lect 38:63, 1942–1943. Schiffman SS: Drugs influencing taste and smell perception. In: Getchell TV, Bartoshuk LM, Doty RL, Snow RL (eds): Smell and Taste in Health and Disease. New York, Raven Press, 1991, pp 845–850. Schiffman SS: Taste and smell losses in normal aging and disease. JAMA 276:1357, 1997. Slotnick BM, Kaneko N: Role of mediodorsal thalamic nucleus in olfactory discrimination learning in rats. Science 214:91, 1981. Sumner D: Disturbances of the senses of smell and taste after head injuries. In: Vinken PJ, Bruyn GW (eds): Handbook of Clinical Neurology. Vol 24. Amsterdam, North-Holland, 1975, pp 1–25. Sumner D: Post-traumatic ageusia. Brain 90:187, 1967.


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Neurology_Adams. Sumner D: Post-traumatic ageusia. Brain 90:187, 1967. Welge-Luessen A, Temmel A, Quint C, et al: Olfactory function in patients with olfactory groove meningiomas. J Neurol Neurosurg Psychiatry 70:218, 2001. Wysocki CJ, Meredith H: The vomeronasal system. In: Finger TE, Silver WL (eds): Neurobiology of Taste and Smell. New York, Wiley, 1987, pp 125–150. Young JM, Trask BJ. The sense of smell: genomics of vertebrate odorant receptors. Hum Mol Genet 11:1153, 2002. Zilstorff W: Parosmia. J Laryngol Otol 80:1102, 1966.


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Neurology_Adams. Young JM, Trask BJ. The sense of smell: genomics of vertebrate odorant receptors. Hum Mol Genet 11:1153, 2002. Zilstorff W: Parosmia. J Laryngol Otol 80:1102, 1966. Figure 11-1. Diagram illustrating the relationships between the olfactory receptors in the nasal mucosa and neurons in the olfactory bulb and tract. Cells of the anterior olfactory nucleus are found in scattered groups caudal to the olfactory bulb. Cells of the anterior olfactory nucleus make immediate connections with the olfactory tract. They project centrally via the medial olfactory stria and to contralateral olfactory structures via the anterior commissure. Inset: diagram of the olfactory structures on the inferior surface of the brain (see text for details). Chapter 11 Disorders of Smell and Taste Disturbances of Vision


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Neurology_Adams. The importance of the visual system is reflected by the magnitude of its representation in the central nervous system. A large part of the cerebrum is committed to vision, including perception of the form and color of objects, the perception of spatial relationships and motion, and the visual control of movements. The optic nerve, which is a tract of the central nervous system, contains more than a million fibers (compared to 50,000 in the auditory nerve). The visual system also has special significance in that study of this system has greatly advanced our knowledge of both the organization of all sensory neuronal systems and the relation of perception to cognition. Indeed, we know more about vision than about any other sensory function. Furthermore, the eyes, because of their diverse composition of epithelial, vascular, neural, and pigmentary tissues, are virtually a medical microcosm, susceptible to many diseases, and its tissues are available for inspection through a transparent


Neurology_Adams

Neurology_Adams. of epithelial, vascular, neural, and pigmentary tissues, are virtually a medical microcosm, susceptible to many diseases, and its tissues are available for inspection through a transparent medium.


Neurology_Adams

Neurology_Adams. Impairment of visual function, expressed as defects in acuity and alterations of visual fields, obviously stands as the most important symptom of eye disease. A number of terms are commonly used to describe visual loss. Amaurosis is a general term that refers to partial or complete loss of sight. Amblyopia refers to any monocular deficit in vision that occurs in the presence of normal ocular structures. A major cause of amblyopia is the suppression by the brain of vision from one eye during early childhood caused by either strabismus, anisometropia (a significant difference in refractive error), or by media opacities. Nyctalopia is a term for poor twilight or night vision and is associated with extreme myopia, cataracts, vitamin A deficiency, retinitis pigmentosa, and, often, color blindness. There are also a number of positive visual symptoms that are named based on their characteristics, phosphenes, migrainous scintillations, visual illusions, and hallucinations. Irritation,


Neurology_Adams

Neurology_Adams. blindness. There are also a number of positive visual symptoms that are named based on their characteristics, phosphenes, migrainous scintillations, visual illusions, and hallucinations. Irritation, redness, photophobia, pain, diplopia and strabismus, changes in pupillary size, and drooping or closure of the eyelids are other major ocular symptoms and signs. Impairment of vision may be unilateral or bilateral, sudden or gradual, episodic or enduring.


Neurology_Adams

Neurology_Adams. The common causes of failing eyesight vary with age. In infancy, congenital defects, retinopathy of prematurity, severe myopia, hypoplasia of the optic nerve, optic pits, and coloboma are the main causes. In childhood and adolescence, nearsightedness or myopia, and amblyopia as a result of strabismus are the usual causes (see Chap. 13), although a pigmentary retinopathy or a retinal, optic nerve, or suprasellar tumor may also begin at this age. In middle age, usually beginning in the fifth decade, a progressive loss of accommodation (presbyopia) is almost invariable (at this age, half or more of the amplitude of accommodative power is lost and must be replaced by plus lenses). Still later in life, cataracts, glaucoma, retinal vascular occlusion and detachments, macular degeneration, and tumor, unilateral or bilateral, are the most frequent causes of visual impairment.


Neurology_Adams

Neurology_Adams. Episodic visual loss in early adult life, often hemianopic, is often the result of migraine. The other important cause of transient (weeks) monocular visual loss in this age period is optic neuritis, often a harbinger of multiple sclerosis. Amaurosis in the child or young adult may also be caused by systemic lupus erythematosus and the related antiphospholipid syndrome (Digre et al), or by migraine, or there may be no discernible cause. Later in life, transient monocular blindness, or amaurosis fugax, lasting minutes to hours is more common; it is caused by vascular disease, particularly stenosis of the ipsilateral carotid artery. Table 12-1 lists the main causes of episodic monocular visual loss. Of course, at any age, diseases of the retina and of other components of the ocular apparatus are important causes of progressive visual loss.


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Neurology_Adams. In the investigation of a disturbance of vision, one inquires as to what the patient means when he claims that he cannot see properly, for the disturbance in question may vary from nearor farsightedness to diplopia, partial syncope, dizziness, or a hemianopia. Fortunately, the patient’s statement can be checked by the measurement of visual acuity, which is an essential part of the ocular examination. Inspection of the refractive media and the optic fundi, the testing of pupillary reflexes, color vision, and the plotting of visual fields complete this part of the examination. Examination of the eye movements is also essential, particularly if amblyopia predicated on an early life strabismus is suspected, as discussed in Chap. 13.


Neurology_Adams

Neurology_Adams. In the measurement of distance visual acuity the Snellen chart, which contains letters (or numbers or pictures) arranged in rows of decreasing size, is used (Fig. 12-1A). Each eye is tested separately at a distance of 20 ft. Spectacles should be worn if they are required for distance. The letter at the top of the chart subtends 5 min of an arc at a distance of 200 ft (or roughly 60 m). The patient follows rows of letters that can normally be read at lesser distances. Acuity is reported as a nonmathematical fraction that represents the distance at which the patient has read the chart and the distance at which a person with normal vision would be able to read a letter of the same size. Thus, at distance of 20 ft if the patient can read only the top letter on the chart, which would be normally be visible at 200 ft, the acuity is expressed as 20/200 (if the distance is measured in meters, it is 6/60). If the patient’s eyesight is normal, the visual acuity will equal 20/20, or 6/6,


Neurology_Adams

Neurology_Adams. normally be visible at 200 ft, the acuity is expressed as 20/200 (if the distance is measured in meters, it is 6/60). If the patient’s eyesight is normal, the visual acuity will equal 20/20, or 6/6, corresponding to the eighth line on most charts. Many persons, especially during youth, can read at 20 ft the line that can ‘normally’ be read at 15 ft from the chart, and thus have acuity of 20/15.


Neurology_Adams

Neurology_Adams. For bedside testing, a “near card” or newsprint held 14 in from the eyes can be used, and the results expressed in a distance equivalent as if a distance chart had been used (Fig. 12-1B). Here, the Jaeger system is used (J1 is “normal” vision, corresponding to the line 20/20 on a Snellen chart, J7 to 20/50, J13 to 20/100, and J16 to 20/200). In young children, acuity can be estimated by having them match symbols on an eye chart to choices on a card or mimic the examiner’s finger movements at varying distances. The Teller acuity cards estimate visual acuity by evaluating a child’s preference (and hence ability) to view cards with increasingly fine stripes.


Neurology_Adams

Neurology_Adams. When visual acuity is reduced, it is helpful to use a pinhole to judge whether a refractive error or other ocular disturbances are the cause. The pinhole permits a narrow shaft of light to fall on the fovea (the area of greatest visual acuity) and eliminates the need for light to be correctly focused by the anterior segments of the eye. If the acuity improves to normal with a pinhole, one can conclude that the reduced vision relates to a defect in the optical media (lens, cornea, aqueous, vitreous) of the eye.