Neurology_Adams

Neurology_Adams. Figure 4-1. Overview of the components of the basal ganglia in coronal view. The main nuclei of the basal ganglia are represented in light brown, as labeled on the right. Figure 4-2. Diagram of the basal ganglia in the coronal plane, illustrating the main interconnections (see text for details). The pallidothalamic connections are illustrated in Fig. 4-3. Figure 4-3. Schematic illustration of major efferent and afferent connections of the basal ganglia. The green lines indicate neurons with excitatory effects, whereas the red lines indicate inhibitory influences. (See text for details and Fig. 4-2.) (Reproduced with permission from Kandel ER, Schwartz JH, Jessell TM: Principles of Neural Science, 5th ed. New York: McGraw-Hill, 2013.)


Neurology_Adams

Neurology_Adams. Figure 4-4. A. Schematic diagram of the cortical–basal ganglia–thalamic circuits showing the main neurotransmitter pathways and their effects. Dopaminergic neurons arising in the pars compacta of the substantia nigra have an excitatory influence on the direct pathway (via D1 receptors) and an inhibitory effect on the indirect pathway (via D2 receptors). B. In Parkinson disease, hypokinesia is thought to result from reduced dopamine input from the substantia nigra to the striatum. As a result, decreased inhibition of the globus pallidus interna by the direct pathway, and increased excitation of the globus pallidus interna by the indirect pathway, leads to increased inhibitory drive of the thalamus and therefore decreased excitation of the cortex. C. In Huntington disease, there is degeneration of the striatum. For the direct pathway, there is overall a net inhibition of the globus pallidus interna (due to decreased inhibition from the striatum, increased inhibition from the globus


Neurology_Adams

Neurology_Adams. of the striatum. For the direct pathway, there is overall a net inhibition of the globus pallidus interna (due to decreased inhibition from the striatum, increased inhibition from the globus pallidus externa, and decreased excitation from the subthalamic nucleus). For the indirect pathway, there is less inhibition of the globus pallidus externa, leading to more inhibition of the subthalamic nucleus, less excitation of globus pallidus interna. In sum, there is less inhibition of the thalamus, and increased excitation of the cortex, leading to hyperkinetic movements. (continued)


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Neurology_Adams. Figure 4-5. A. Characteristic dystonic deformities in a young boy with dystonia musculorum deformans. B. Sporadic instance of severe axial dystonia with onset in adult life. C. Incapacitating postural deformity in a young man with dystonia. (Photos courtesy of Dr. I. S. Cooper and Dr. Joseph M. Waltz.) Figure 4-6. Tremor branch diagram.


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Neurology_Adams. Dr. Joseph M. Waltz.) Figure 4-6. Tremor branch diagram. Figure 4-7. Types of tremor. In each, the lowest trace is an accelerometric recording from the outstretched hand; the upper two traces are surface EMG from the wrist extensor (upper) and flexor (middle) muscle groups. A. A physiologic tremor; there is no evidence of synchronization of EMG activity. B. Essential (familial) tremor; the movements are very regular and EMG bursts occur simultaneously in antagonistic muscle groups. C. Neuropathic tremor; movements are irregular and EMG bursts vary in timing between the two groups. D. Parkinsonian (“rest”) tremor; EMG bursts alternate between antagonistic muscle groups. Calibration is 1 s. (Courtesy of Dr. Robert R. Young.)


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Neurology_Adams. Figure 4-8. Dystonic movement disorders. A. Young man with severe spasmodic retrocollis. Note hypertrophy of sternocleidomastoid muscles. B. Meige syndrome of severe blepharospasm and facial-cervical dystonia. C. Characteristic athetoid-dystonic deformities of the hand in a patient with tardive dyskinesia. (Photographs courtesy of Dr. Joseph M. Waltz.)


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Neurology_Adams. Chapter 4 Disorders of Movement and Posture +++++––––––IndirrectpathwaySubstantianigra parscompactaCortexCortexCaudate/putamen(striatum)VA/VL complex ofthalamusGlobus pallidus,external segmentSubthalamicnucleusGlobus pallidus,internal segmentD1D2A. Normal configuration of basal ganglia connections +++++–––––B. Parkinson disease (hypokinetic)Substantianigra parscompactaCortexCortexDecreasedexcitationMore tonicinhibitionDiminishedCaudate/putamen(striatum)VA/VL complex ofthalamusGlobus pallidus,external segmentSubthalamicnucleusIncreasedIncreasedDegeneratedGlobus pallidus,internal segmentD1D2 +++++––––––C. Huntington disease (hyperkinetic)Substantianigra parscompactaCortexCortexIncreasedexcitationLess tonicinhibitionCaudate/putamen(striatum)VA/VL complex ofthalamusGlobus pallidus,external segmentSubthalamicnucleusIncreasedDiminishedDegeneratedGlobus pallidus,internal segmentD1D2 Figure 4-4. (Continued) Ataxia and Disorders of Cerebellar Function


Neurology_Adams

Neurology_Adams. Figure 4-4. (Continued) Ataxia and Disorders of Cerebellar Function The cerebellum is primarily responsible for the coordination of movements, especially skilled voluntary ones, the control of posture and gait, and the regulation of muscular tone. In addition, the cerebellum may play a role in the modulation of the emotional state and some aspects of cognition. The mechanisms by which these functions are accomplished have been the subject of intense investigation by anatomists and physiologists. Their studies have yielded a mass of data, testimony to the complexity of the organization of the cerebellum and its afferent and efferent connections. A coherent picture of cerebellar function has emerged, and it is possible to relate certain of the symptoms and signs of cerebellar disease to discrete anatomic and functional units.


Neurology_Adams

Neurology_Adams. Knowledge of cerebellar function has been derived mainly from the study of natural and experimental ablative lesions and to a lesser extent from stimulation of the cerebellum, which actually produces little in the way of movement or alterations of induced movement. Furthermore, none of the motor activities of the cerebellum reaches conscious kinesthetic perception; its main role, a critical one, is to assist in the modulation of willed movements. The following discussion of cerebellar structure and function has, of necessity, been simplified; a fuller account can be found in the writings of Jansen and Brodal, of Gilman, and of Thach and colleagues.


Neurology_Adams

Neurology_Adams. Early studies of the comparative anatomy and fiber connections of the cerebellum led to its subdivision into three parts (Fig. 5-1 and Table 5-1): (1) The flocculonodular lobe, located inferiorly, which is phylogenetically the oldest portion of the cerebellum and is much the same in all animals (hence its former designation as archicerebellum). It is separated from the main mass of the cerebellum, the cerebellar hemispheres, by the posterior fissure. (2) The anterior lobe, or paleocerebellum, which is the portion rostral to the primary fissure. In lower animals, the anterior lobe constitutes most of the cerebellum, but in humans it is relatively small, consisting of the anterosuperior vermis and the contiguous paravermian cortex. (3) The posterior lobe, or neocerebellum, consisting of the middle divisions of the vermis and their large lateral extensions. The major portion of the cerebellum, the cerebellar hemispheres proper, falls into this, the largest, subdivision.


Neurology_Adams

Neurology_Adams. The cerebellum is connected to the brain through three paired peduncles: the superior, which is efferent with the exception of the ventral spinocerebellar and tectocerebellar tracts; the middle, which contains the main input to the cerebellum from the pons; and the inferior, through which the vestibular and spinal input enters the cerebellum. The posterolateral walls of the fourth ventricle are bounded by these peduncles (Fig. 5-2 and Table 5-2).


Neurology_Adams

Neurology_Adams. The anatomic subdivision of the cerebellum corresponds roughly with its functional organization, based on the arrangement of its afferent fiber connections. The flocculonodular lobe receives special proprioceptive impulses from the vestibular nuclei and is therefore also referred to as the vestibulocerebellum; it is concerned essentially with equilibrium. The anterior vermis and part of the posterior vermis are referred to as the spinocerebellum, since projections to these parts derive to a large extent from the proprioceptors of muscles and tendons in the limbs and are conveyed to the cerebellum in the dorsal spinocerebellar tract (from the lower limbs) and the ventral spinocerebellar tract (upper limbs). The main influences of the spinocerebellum appear to be on posture and muscle tone. The neocerebellum derives its afferent fibers indirectly from the cerebral cortex via the pontine nuclei and through the middle cerebellar peduncles (brachium pontis). This portion of the cerebellum


Neurology_Adams

Neurology_Adams. The neocerebellum derives its afferent fibers indirectly from the cerebral cortex via the pontine nuclei and through the middle cerebellar peduncles (brachium pontis). This portion of the cerebellum is concerned primarily with the coordination of skilled movements that are initiated at a cerebral cortical level.


Neurology_Adams

Neurology_Adams. Largely on the basis of ablation experiments in animals, three characteristic physiologic patterns corresponding to these major divisions of the cerebellum have been delineated. These constellations find some, but not perfect, similarities in the clinical syndromes that are observed when various parts of the cerebellum are damaged in patients. Lesions of the nodulus and flocculus (flocculonodular lobe) in animals have been associated with a disturbance of equilibrium and frequently with nystagmus; individual movements of the limbs are not affected. Anterior lobe ablation in primates results in increased shortening and lengthening reactions (the reactions of the muscle to passive flexion or extension at a joint), somewhat increased tendon reflexes, and an exaggeration of the postural reflexes, particularly the “positive supporting reflex,” which consists of extension of an animal’s limb in response to light pressure on the foot pad. Ablation of a cerebellar hemisphere in cats and dogs


Neurology_Adams

Neurology_Adams. particularly the “positive supporting reflex,” which consists of extension of an animal’s limb in response to light pressure on the foot pad. Ablation of a cerebellar hemisphere in cats and dogs yields inconsistent results, but in monkeys it causes hypotonia and clumsiness of the ipsilateral limbs; if the dentate nucleus is included in the hemispheric ablation, these abnormalities are more enduring and the limbs also show an ataxic, or “intention” tremor. Again, these find only approximate similarities to clinical signs in patients with lesions of the cerebellum as discussed below.


Neurology_Adams

Neurology_Adams. The studies of Chambers and Sprague and of Jansen and Brodal have demonstrated that in respect to both its afferent and efferent projections in animals, the cerebellum is organized into longitudinal (sagittal) rather than transverse zones. There are three longitudinal zones—the vermian, paravermian or intermediate, and lateral—and there seems to be considerable overlap from one to another. Sprague and Chambers, on the basis of their investigations in cats, concluded that the vermian zone coordinates movements of the eyes and body with respect to gravity, and movement of the head in space. The intermediate zone, which receives both peripheral and central projections (from motor cortex), influences postural tone and also individual movements of the ipsilateral limbs. The lateral zone is concerned mainly with coordination of movements of the ipsilateral limbs but is also involved in other functions.


Neurology_Adams

Neurology_Adams. The efferent fibers of the cerebellar cortex, which consist essentially of the axons of Purkinje cells in both humans and animals, project onto the deep cerebellar nuclei (see later). The projections from Purkinje cells are inhibitory whereas those from the nuclei are excitatory on other parts of the motor nervous system. According to the scheme of Jansen and Brodal, cells of the vermis project mainly to the fastigial nucleus; those of the intermediate zone, to the globose and emboliform nuclei (that are combined in humans as the interpositus, or “interposed” nucleus); and those of the lateral zone, to the dentate nucleus.


Neurology_Adams

Neurology_Adams. The deep cerebellar nuclei, in turn, project to certain thalamic and brainstem nuclei via two main pathways: fibers from the dentate and interposed nuclei form the superior cerebellar peduncle, enter the upper pontine tegmentum as the brachium conjunctivum, decussate at the level of the inferior colliculus, and ascend to the ventrolateral nucleus of the thalamus and, to a lesser extent, to the intralaminar thalamic nuclei (Fig. 5-3). Some of the ascending fibers, soon after their decussation, synapse in the red nucleus, but most of them traverse this nucleus without terminating, and pass on to the thalamus. Ventral thalamic nuclear groups that receive these ascending efferent fibers project to the supplementary motor cortex of that side. Since the pathway from the cerebellar nuclei to the thalamus and then on to the motor cortex is crossed, and the connection from the motor cortex through the corticospinal tract is again crossed, the effects of a lesion in one cerebellar hemisphere


Neurology_Adams

Neurology_Adams. thalamus and then on to the motor cortex is crossed, and the connection from the motor cortex through the corticospinal tract is again crossed, the effects of a lesion in one cerebellar hemisphere are manifest by signs on the ipsilateral side of the body.


Neurology_Adams

Neurology_Adams. One special pathway forms a loop, called the Guillain-Mollaret triangle that is of clinical interest. A small group of fibers of the superior cerebellar peduncle, following their decussation, synapse in the red nucleus and then descend in the ventromedial tegmentum of the brainstem via the central tegmental fasciculus, terminating in the inferior olivary nuclei of the medulla (as well as in reticular nuclei of the pons, but these are not part of the feedback loop of the triangle). The olivary nuclei, in turn, project via the inferior cerebellar peduncle back to the cerebellum, mainly the anterior lobe, thus completing a cerebellar–reticular–cerebellar feedback system (Fig. 5-4). The clinical syndrome of oculopalatal tremor results from lesions in the central tegmental fasciculus component of the triangle.


Neurology_Adams

Neurology_Adams. The fastigial nucleus sends fibers to the vestibular nuclei of both sides and, to a lesser extent, to other nuclei of the reticular formation of the pons and medulla. There are also direct fiber connections with the alpha and gamma motor neurons of the spinal cord. The inferior olivary nuclei project via the restiform body (inferior cerebellar peduncle) to the contralateral cerebellar cortex and corresponding parts of the deep cerebellar nuclei. Thus the cerebellum influences motor activity through its connections with the motor cortex and brainstem nuclei and their descending motor pathways (see Evarts and Thach). Chapter 4 details the integration of basal ganglionic influences with those of the cerebellum by their confluence in the anterior thalamic nuclei.


Neurology_Adams

Neurology_Adams. Experimental observations suggest that the cerebellar cortex is somatotopically organized, but not in the same manner as the motor and sensory cortices of the cerebral hemispheres. Stimulation of the cerebellar cortex does not produce movement of body parts. Moreover, motor function of body parts is not represented in a continuous fashion in the cerebellar cortex and instead corresponds to small discontinuous patches. There is an approximate motor specificity in that the legs, trunk, and gait are affected in a restricted fashion with lesions of the vermis and coordination of limb movements is affected by lesions of the body of the cerebellar hemispheres but this does not simulate the refined organization observed in the cerebral cortex. However, a sensory organization that reflects the topography of the body has been confirmed by mapping local peripheral sensory stimuli to corresponding sites of the cerebellar cortex in animals, and by analyzing the subtle motor effects produced by


Neurology_Adams

Neurology_Adams. topography of the body has been confirmed by mapping local peripheral sensory stimuli to corresponding sites of the cerebellar cortex in animals, and by analyzing the subtle motor effects produced by stimulation of parts of the cerebellar cortex. Many published diagrams of the cerebellum with an overlaid homunculus reflect sensory, not motor, topographic organization. The interesting history of ideas regarding cerebellar localization and current understanding are reviewed by Manni and Petrosini.


Neurology_Adams

Neurology_Adams. Role of the Deep Cerebellar Nuclei The physiologic studies of Allen and Tsukahara and of Thach and colleagues produced some of the most important data pertaining to the role of the deep cerebellar nuclei. These investigators studied the effects of cooling the deep nuclei during a projected movement in the macaque monkey. Their observations, coupled with established anatomic data, permit the following conclusions.


Neurology_Adams

Neurology_Adams. The dentate nucleus receives information indirectly from the premotor and supplementary motor cortices via the pontocerebellar system and helps to initiate volitional movements. These movements are accomplished via efferent projections from the dentate nucleus to the ventrolateral thalamus and motor cortex. The dentatal neurons have been shown to fire just before the onset of volitional movements, and inactivation of the dentatal neurons delays the initiation of such movements. The interpositus nucleus also receives projections from the cortex via the crossed pontocerebellar fibers; in addition, it receives spinocerebellar projections via the intermediate zone of the cerebellar cortex. The spinocerebellar projections convey information from Golgi tendon organs, muscle spindles, cutaneous afferents, and spinal cord interneurons involved in movement. The interpositus nucleus fires in relation to a movement once it has started. Also, the interpositus nucleus appears to be responsible for


Neurology_Adams

Neurology_Adams. and spinal cord interneurons involved in movement. The interpositus nucleus fires in relation to a movement once it has started. Also, the interpositus nucleus appears to be responsible for making volitional oscillations (alternating movements). Its cells fire in tandem with these actions and the regularity and amplitude of movements become impaired when these cells are inactivated. In addition, Thach pointed out that the nucleus interpositus normally damps physiologic tremor and suggested that this may play a part in the genesis of the intention tremor described further on. The fastigial nucleus receives projections from the spinocerebellar fibers and, like the interpositus, projects to the vestibular nuclei. It controls antigravity and other muscle synergies in standing and walking; ablation of this nucleus greatly impairs these motor activities.


Neurology_Adams

Neurology_Adams. There are complex physiologic relationships among the deep nuclei, and cerebellar cortical regions generally have inhibitory influences on the deep nuclei. The flocculonodular lobe has among the most complex influences, being inhibitory to the fastigial nucleus but also projecting directly in an inhibitory manner to the lateral vestibular (Deiters) nucleus. The vestibular nuclei, and in particular the lateral one, may be considered, in effect the equivalent of a deep cerebellar nucleus. Neuronal Organization of the Cerebellar Cortex


Neurology_Adams

Neurology_Adams. Neuronal Organization of the Cerebellar Cortex Coordinated and fluid movements of the limbs and trunk result from a neuronal organization in the cerebellum that permits an ongoing and almost instantaneous comparison between desired and actual movements while the movements are being carried out. An enormous number of neurons are committed to these tasks, as attested by the fact that the cerebellum contributes only 10 percent to the total weight and volume of the brain but contains half of the brain’s neurons. Also, it has been estimated that there are 40 times more afferent axons than efferent axons in the various cerebellar pathways—a reflection of the enormous amount of incoming (sensory) information that is required for the control of motor function.


Neurology_Adams

Neurology_Adams. The cerebellar cortex is configured as a stereotyped three-layered structure, the molecular, Purkinje, and granular layers, that together contain five types of neurons (Fig. 5-5). In its relatively regular geometry, it is similar to the columnar architecture of the cerebral cortex, but it differs in the greater degree of intracortical feedback between neurons and the convergent nature of input fibers. The outermost molecular layer of the cerebellum contains two types of inhibitory neurons, the stellate cells and the basket cells. They are interspersed among the dendrites of the Purkinje cells, the cell bodies of which lie in the underlying layer. The Purkinje cell axons constitute the main output of the cerebellar cortex, which is directed at the deep cerebellar and vestibular nuclei described above. Purkinje cells are, as mentioned earlier, entirely inhibitory and utilize the neurotransmitter gamma-aminobutyric acid (GABA). The innermost granular layer contains an enormous number of


Neurology_Adams

Neurology_Adams. above. Purkinje cells are, as mentioned earlier, entirely inhibitory and utilize the neurotransmitter gamma-aminobutyric acid (GABA). The innermost granular layer contains an enormous number of densely packed granule cells and a few larger Golgi interneurons. Axons of the granule cells travel long distances as parallel fibers, which are oriented along the long axis of the folia and form excitatory synapses with Purkinje cells. Each Purkinje cell is influenced by as many as a million granule cells to produce what has been termed physiologically a “simple spike,” in contrast to the complex spike noted below.


Neurology_Adams

Neurology_Adams. The predominant afferent input to the cerebellum is via the mossy fibers, which are the axons of the spinocerebellar tracts and via the projections from pontine, vestibular, and reticular nuclei. They enter through all three cerebellar peduncles, mainly the middle (pontine input) and inferior (vestibulocerebellar) ones. Mossy fibers ramify in the granule layer and excite Golgi and granule neurons through special synapses termed cerebellar glomeruli. The other main afferent input is via the climbing fibers, which originate in the inferior olivary nuclei (olives) and communicate somatosensory, visual, and cerebral cortical signals (Figs. 5-5 and 5-6). The climbing fibers, so named because of their vine-like configuration around Purkinje cells and their axons, preserve a topographic arrangement from olivary neuronal groups; a similar topographic arrangement is maintained in the Purkinje cell projections. The climbing fibers have specific excitatory effects on Purkinje cells that result


Neurology_Adams

Neurology_Adams. from olivary neuronal groups; a similar topographic arrangement is maintained in the Purkinje cell projections. The climbing fibers have specific excitatory effects on Purkinje cells that result in prolonged “complex spike” depolarizations. The firing of stellate and basket cells is facilitated by the same parallel fibers that excite Purkinje cells, and these smaller cells, in turn, inhibit the Purkinje cells. These reciprocal relationships form the feedback loops that permit the exquisitely delicate inhibitory smoothing of limb movements that are lost when the organ is damaged.


Neurology_Adams

Neurology_Adams. The uniform cortical structure of the cerebellum can reasonably lead to the notion that the organ has similar effects on all parts of the cerebrum to which it has projections (cortex, basal ganglia, thalamus, etc.). It would follow that the activities of these cerebral structures (motor, cognitive, sensory) may be modulated in similar ways by cerebellar activity.


Neurology_Adams

Neurology_Adams. A number of biochemical aspects of cerebellar function are of interest. Four of the five cell types of the cerebellar cortex (Purkinje, stellate, basket, Golgi) are inhibitory; the granule cells are an exception and are excitatory. Afferent fibers to the cerebellum are of three types, two of which have been mentioned above: (1) mossy fibers, which are the main afferent input to the cerebellum, utilize aspartate. (2) Climbing fibers, which are the axons of cells in the inferior olivary nucleus and project to the Purkinje cells of the opposite cerebellar hemisphere. The neurotransmitter of the climbing fibers is probably glutamate, which acts on amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors. (3) Aminergic fibers, which project through the superior cerebellar peduncle and terminate on the Purkinje and granule cells in all parts of the cerebellar cortex. They are of two types: dopaminergic fibers, which arise in the ventral mesencephalic tegmentum and project to the


Neurology_Adams

Neurology_Adams. terminate on the Purkinje and granule cells in all parts of the cerebellar cortex. They are of two types: dopaminergic fibers, which arise in the ventral mesencephalic tegmentum and project to the interpositus and dentate nuclei and to the granule and Purkinje cells throughout the cortex, and serotonergic neurons, which are located in the raphe nuclei of the brainstem and project diffusely to the granule cell and molecular layer. The granule cell axons elaborate the excitatory transmitter glutamate. All the inhibitory cerebellar cortical neurons appear to utilize GABA. The neurotransmitters of the deep nuclei have not been fully elucidated.


Neurology_Adams

Neurology_Adams. Joseph Babinski and Gordon Holmes cogently analyzed the disturbances of movement and posture that result from lesions of the human cerebellum. For Babinski, the essential function of the cerebellum was the orchestration of muscle synergies in the performance of voluntary movement. A loss or impairment of this function—i.e., asynergia or dyssynergia—resulted in irregularity or fragmentation of the normal motor sequences involved in any given act. This deficit, most apparent in the execution of rapidly alternating movements, was referred to by Babinski as dysor adiadochokinesis, as discussed below. He also pointed out that this was accompanied by certain maladjustments of stance and by catalepsy (perseveration of a posture), features that are not considered prominent by modern observers.


Neurology_Adams

Neurology_Adams. Holmes summarized the effects of cerebellar disease as being in the acceleration and deceleration of movement. He characterized these in a more fundamental way as defects in the rate, range, and force of movement, resulting in an undershooting or overshooting of the target. He used the term “decomposition” to describe the fragmentation of a smooth movement into a series of irregular, jerky components. The terminal tremor, traditionally called intention tremor, and the inability to check the displacement of an outstretched limb, both of which Holmes elegantly described, were attributed to hypotonia, a mechanism no longer accepted. Parts of the hypotheses of both Babinski and Holmes have been sustained by modern physiologic and clinical studies. In an analysis of rapid (ballistic) movements,


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Neurology_Adams. Hallett and colleagues have demonstrated that with cerebellar lesions, there is a prolongation of the interval between the commanded act and the onset of movement. More prominently, there is a derangement of the normal ballistic triphasic agonist–antagonist–agonist motor sequence, referred to in Chaps. 3 and 4. The agonist burst may be too long or too short, or it may continue into the antagonist burst, resulting in excessive agonist–antagonist cocontraction at the onset of movement. These findings may explain what was described by Babinski and Holmes as asynergia, decomposition of movement, but they certainly explain dysmetria. Diener and Dichgans confirmed these fundamental abnormalities in the timing and amplitude of reciprocal inhibition and of cocontraction of agonist–antagonist muscles and remarked that these were particularly evident in pluriarticular movements.


Neurology_Adams

Neurology_Adams. The symptoms produced in animals by ablation of discrete anatomic or functional zones of the cerebellum bear only an imperfect relationship to the symptoms of cerebellar disease in humans. This is understandable for several reasons. Most of the lesions that occur in humans do not respect the boundaries established by experimental anatomists. Even with lesions that are more or less confined to discrete functional zones (e.g., flocculonodular lobe, anterior lobe), it is difficult to identify the resultant clinical syndromes with those produced by ablation of analogous zones in cats, dogs, and even monkeys, indicating that the functional organization of these parts varies from species to species.


Neurology_Adams

Neurology_Adams. Clinical observations affirm what was stated above—that lesions of the cerebellum in humans give rise to the following abnormalities: (1) incoordination (ataxia) of volitional movement; (2) a characteristic tremor (“intention,” or ataxic tremor, by which is meant a side-to-side oscillation as movement approaches a target), described in detail in Chap. 4; (3) disorders of equilibrium and gait; and (4) diminished muscle tone, particularly with acute lesions. (5) Dysarthria, a common feature of cerebellar disease, is probably predicated on a similar incoordination of the muscles of articulation. (6) In addition, the stability of conjugate eye movements is affected, giving rise to impaired ocular pursuit, inaccurate saccades, and pathological nystagmus.


Neurology_Adams

Neurology_Adams. Extensive lesions of one cerebellar hemisphere, especially of the anterior lobe, cause hypotonia, postural abnormalities, ataxia, and mild weakness of the ipsilateral arm and leg, the last of these perceived mostly by the patient. Lesions of the deep nuclei and cerebellar peduncles have the same effects as extensive hemispheral lesions. If the lesion involves a limited portion of the cerebellar cortex and subcortical white matter, there may be surprisingly little disturbance of function, or the abnormality may be greatly attenuated with the passage of time. For example, a congenital developmental defect or an early life cortical atrophy of half of the cerebellum may produce no clinical abnormalities. Lesions involving the superior cerebellar peduncle or the dentate nucleus cause the most severe and enduring cerebellar symptoms, which manifest mostly as ataxia in the ipsilateral limbs. Disorders of stance and gait depend more on vermian than on hemispheral or peduncular involvement.


Neurology_Adams

Neurology_Adams. severe and enduring cerebellar symptoms, which manifest mostly as ataxia in the ipsilateral limbs. Disorders of stance and gait depend more on vermian than on hemispheral or peduncular involvement. Damage in the inferior cerebellum causes vestibulocerebellar symptoms—namely, dizziness, vertigo, vomiting, and nystagmus—in varying proportions. These symptoms often share with disturbances of the vestibular system the feature of worsening with changes in head position.


Neurology_Adams

Neurology_Adams. The most prominent manifestations of cerebellar disease, the abnormalities of intended (volitional) movement, are classified under the general heading of cerebellar incoordination, or ataxia. Following Babinski, the terms dyssynergia, dysmetria, and dysdiadochokinesis came into common usage to describe cerebellar abnormalities of movement. Holmes’s characterization of abnormalities in the rate, range, and force of movement, as mentioned earlier, is less confusing, as becomes apparent from an analysis of even simple movements. These signs are brought out by standard neurologic tests, including finger-to-nose and toe-to-finger movement, running the heel down the opposite shin, or tracing a square in the air with a hand or foot. In performing these maneuvers, the patient should be asked to move the limb to the target accurately and rapidly.


Neurology_Adams

Neurology_Adams. The speed of initiating movement is slowed somewhat in cerebellar disease. In a detailed electrophysiologic analysis of this defect mentioned earlier, Hallett and colleagues noted, in both slow and fast movements, that the initial agonist burst was prolonged and the peak force of the agonist contraction was reduced. Also, there is irregularity and slowing of the movement itself, in both acceleration and deceleration. These abnormalities are particularly prominent as the finger or toe approaches its target. All the foregoing defects in volitional movement are evident in acts that require alternation or rapid change in direction of movement, such as pronation–supination of the forearm or successive touching of each fingertip to the thumb. The normal rhythm of these movements is interrupted by irregularities of force and speed. Even a simple movement may be fragmented (“decomposition” of movement), each component being effected with greater or lesser force than is required. These


Neurology_Adams

Neurology_Adams. by irregularities of force and speed. Even a simple movement may be fragmented (“decomposition” of movement), each component being effected with greater or lesser force than is required. These movement abnormalities together impart a highly characteristic clumsiness to the cerebellar syndromes, an appearance that is not simulated by the weakness of upper or lower motor neuron disorders or by diseases of the basal ganglia.


Neurology_Adams

Neurology_Adams. Normally, deceleration of movement is smooth and accurate, even if sharp changes in the direction of a limb are demanded, as in following a moving target. With cerebellar disease, the velocity and force of the movement are not checked in the normal manner. The excursion of the limb may be arrested prematurely, and the target is then reached by a series of jerky movements. In contrast, the limb may overshoot the mark (hypermetria) because of delayed activation and diminished contraction of antagonist muscles; then the error is corrected by a series of secondary movements in which the finger or toe sways around the target before coming to rest, or moves from side to side a few times on the target itself. This side-to-side movement of the finger as it approaches its mark tends to assume a rhythmic quality; it has traditionally been referred to as intention tremor, or ataxic tremor. The tremor is mainly perpendicular to the trajectory of movement and mostly in the horizontal plane (the


Neurology_Adams

Neurology_Adams. rhythmic quality; it has traditionally been referred to as intention tremor, or ataxic tremor. The tremor is mainly perpendicular to the trajectory of movement and mostly in the horizontal plane (the reason for the latter is not known). The term “intention” as applied to cerebellar tremor, while embedded in neurologic parlance, does not fully capture the necessity for the limb to be in action rather than for the patient to “intend” a movement for the tremor to be manifest. “Action tremor,” however, has been used for an entirely different category of oscillations, as discussed in Chap. 4 so that “ataxic tremor” or “goal directed action tremor” may be preferable terms.


Neurology_Adams

Neurology_Adams. In addition to intention tremor, there may be a coarse, irregular, wide-range tremor that may be present whenever the patient activates limb muscles, either to sustain a posture or to effect a large amplitude proximal movement. It is traditionally elicited by having the patient hold the arms out to the sides with elbows bent (“wing-beating tremor”). Holmes called it rubral tremor; however, although the red nucleus may be the site of the lesion, the nucleus itself is not necessarily involved in this type of tremor. Instead, it is a result of interruption of the fibers of the superior cerebellar peduncle, which traverse the nucleus, for which reason it may be more properly called “cerebellar outflow tremor.” Also, with certain sustained postures (e.g., with arms extended or hands on knees), the patient with cerebellar disease may develop a rhythmic oscillation of the fingers having much the same tempo as a parkinsonian tremor. A rhythmic tremor of the head or upper trunk (3 to 4 per


Neurology_Adams

Neurology_Adams. the patient with cerebellar disease may develop a rhythmic oscillation of the fingers having much the same tempo as a parkinsonian tremor. A rhythmic tremor of the head or upper trunk (3 to 4 per second) called titubation, mainly in the anteroposterior plane, often accompanies midline cerebellar disease, but may also be a manifestation of essential tremor (see further on).


Neurology_Adams

Neurology_Adams. Cerebellar lesions commonly give rise to a disorder of speech, which may take one of two forms: either a slow, slurring dysarthria, or a scanning dysarthria with variable intonation, so-called because words are broken up into syllables, as when a line of poetry is scanned for meter. The typical cerebellar speech simulates the abnormality of limb movements in that the rhythm and amplitude of phonation and articulation are irregular, imparting a pattern that is distinguishable from spastic and extrapyramidal speech and may be so severe as to be incomprehensible. The scanning pattern of speech disorder is uniquely cerebellar; in addition to its scanning quality, speech is slow, and each syllable, after an involuntary interruption, may be uttered with less force or more force (“explosive speech”) than is natural. The scanning and slurred patterns may, of course, be combined. Urban and associates deduced from cases of cerebellar infarction that the articulatory muscles are controlled from


Neurology_Adams

Neurology_Adams. than is natural. The scanning and slurred patterns may, of course, be combined. Urban and associates deduced from cases of cerebellar infarction that the articulatory muscles are controlled from the rostral paravermian area of the anterior lobe, and this area is affected in most cases with dysarthria.


Neurology_Adams

Neurology_Adams. Ocular movement may be altered as a result of cerebellar disease, specifically if vestibular connections are involved (Thach and Montgomery). Patients with cerebellar lesions are unable to hold eccentric positions of gaze, resulting in a special type of nystagmus and the need to make rapid repetitive saccades to look eccentrically (saccadic substitution). Conjugate voluntary gaze can be accomplished only by a series of jerky movements. Smooth pursuit movements are slower than normal and require that the patient make small “catch-up” saccades in an attempt to keep the moving target near the fovea. On attempted refixation to a target, the eyes overshoot the target and then oscillate through several corrective cycles until fixation is attained. It will be recognized that these nystagmoid abnormalities, as well as those of speech, resemble the abnormalities of ataxic movements of the limbs. Skew deviation (vertical displacement of one eye), vertical nystagmus, ocular flutter, and ocular


Neurology_Adams

Neurology_Adams. as well as those of speech, resemble the abnormalities of ataxic movements of the limbs. Skew deviation (vertical displacement of one eye), vertical nystagmus, ocular flutter, and ocular myoclonus (opsoclonus) may also be the result of cerebellar disease; these abnormalities and other effects of cerebellar lesions on ocular movement are discussed in Chap. 13.


Neurology_Adams

Neurology_Adams. Disorders of Equilibrium and Gait The patient with cerebellar disease has variable degrees of difficulty in standing and walking, as described more fully in Chap. 6. Standing with feet together may be impossible or maintained only briefly before the patient pitches to one side or backward. Closing the eyes may worsen this difficulty slightly. The Romberg sign (which signifies impaired proprioceptive input), however, is not dramatically evident in cerebellar disease if the patient is allowed to steady himself before closing his eyes. In walking, the patient’s steps are uneven and placement of each foot is inconsistent, resulting in unexpected lurching, sometimes most apparent during turns.


Neurology_Adams

Neurology_Adams. Careful clinicoanatomic correlation studies indicate that the disequilibrium syndrome with normal movements of the limbs corresponds more closely with lesions of the anterior vermis than with those of the flocculus and nodulus (essentially, the posterior vermis). This statement is based in part on the study of cerebellar degeneration in alcoholics (see Chap. 41). In such patients, the cerebellar disturbance is often limited to abnormal stance and gait and the pathologic changes are restricted to the anterior parts of the superior vermis. In more severely affected patients, who also manifest impaired coordination of the limbs, the changes are found to extend laterally from the vermis, involving the anterior portions of the anterior lobes when the legs are affected and more posterior portions of the anterior lobes when the arms are affected.


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Neurology_Adams. Unlike the animal experiments mentioned earlier, it is uncertain if disequilibrium can result from lesions of the flocculonodular lobe alone. Attribution of gait instability to damage in this area rests on the observation that medulloblastomas may cause unsteadiness but no tremor or incoordination of the limbs. Insofar as these tumors are thought to originate from cell rests in the posterior medullary velum, at the base of the nodulus, it has been inferred that the disturbance of equilibrium results from involvement of this portion of the cerebellum. By the time such tumors are imaged or viewed at operation or autopsy, however, they have spread beyond the confines of the nodulus, and strict clinicopathologic correlations are not possible.


Neurology_Adams

Neurology_Adams. The point to be made is that midline anterior cerebellar lesions may produce solely a disorder of stance and gait, i.e., nystagmus, dysarthria, and limb ataxia are absent. Moreover, the entire problem may be missed if the examination does not include an assessment of the patient’s ability to stand and walk. This refers to a decrease in the normal resistance that is offered by muscles to passive manipulation. It is the least conspicuous of the cerebellar signs of disease but may explain certain clinical features of the ataxic syndrome. As mentioned earlier, Holmes believed that hypotonia was a fundamental defect in cerebellar disease, accounting not only for the defects in postural fixation (see later) but also for certain elements of ataxia and the tremor.


Neurology_Adams

Neurology_Adams. Hypotonia is related to a depression of gamma and alpha motor neuron activity, as discussed in Chap. 3. Experimentally in cats and monkeys, acute cerebellar lesions and hypotonia are associated with a depression of fusimotor efferent and spindle afferent activity. With the passage of time, fusimotor activity is restored and hypotonia disappears (Gilman et al).


Neurology_Adams

Neurology_Adams. Hypotonia is much more apparent with acute than with chronic lesions and may be demonstrated in a number of ways. A conventional test for hypotonia is to tap the wrists of the outstretched arms and to detect a displacement through a wider range than normal in the affected limb (or both limbs in diffuse cerebellar disease), sometimes causing the limb to oscillate; this is presumably the result of a failure of the hypotonic muscles to fixate the arm at the shoulder. Another test for hypotonia is to shake the affected limb and demonstrate that the flapping movements of the hand are of wider excursion than normal. If the patient places his elbows on the table with the arms flexed and the hands are allowed to hang limply, the hand of the hypotonic limb will sag. If the standing patient is rotated to and fro at the shoulders, the hypotonic arm will be seen to continue to swing after the other has come to rest. Holmes also attributed pendular knee jerks to hypotonia but he described a more


Neurology_Adams

Neurology_Adams. to and fro at the shoulders, the hypotonic arm will be seen to continue to swing after the other has come to rest. Holmes also attributed pendular knee jerks to hypotonia but he described a more complex phenomenon in which the normal contraction of the antagonist hamstring fails to occur. This deficiency may be palpated by the examiner during reflex testing. Babinski also was impressed with gross alterations of posture related to hypotonia. These take the form of extension of the neck and involuntary bending of the knees, which are apparent when the patient is lifted from a bed or chair or upon first standing, or slumping of the shoulder on the affected side.


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Neurology_Adams. Failure to check a movement is a closely related phenomenon. Thus, after strongly flexing one arm against a resistance that is suddenly released, the patient may be unable to check the flexion movement, to the point where the arm may strike the face. This is the result of a delay in contraction of the triceps muscle, which ordinarily would arrest overflexion of the arm. Stewart and Holmes, who first described this test, made the point that when resistance to flexion is suddenly removed, the normal limb moves only a short distance in flexion and then rebounds very briefly in the opposite direction. Thus, although the two are often conflated, there is a subtle difference between the signs of deficient checking and an excessive rebound of the limb that follows.


Neurology_Adams

Neurology_Adams. Patients with these various abnormalities of tone may show little or no impairment of motor power (see below), indicating that the maintenance of posture involves more than the voluntary contraction of muscles. It is noteworthy that the signs of cerebellar dysfunction (dysmetria, clumsiness, tremor) are absent in the hypotonic muscles of peripheral nerve disease—indicating that the cerebellum exerts a unique modulating effect on movement that is beyond its control of muscle tone. Other Symptoms of Cerebellar Disease


Neurology_Adams

Neurology_Adams. Other Symptoms of Cerebellar Disease It has been stated by some authors that there is a slight loss of muscular power and fatigability of muscle (asthenia) with acute cerebellar lesions. Insofar as these symptoms cannot be explained by other disturbances of motor function, they may be regarded as primary manifestations of cerebellar disease, but they are never severe or persistent and are of little clinical importance; anything approaching a hemiparesis in distribution or severity is not attributable to cerebellar disease.


Neurology_Adams

Neurology_Adams. Myoclonic movements—i.e., brief (50to 100-ms), random contractions of muscles or groups of muscles—are, in some disease processes, combined with cerebellar ataxia. When multiple myoclonic jerks mar a volitional movement, they may be mistaken for an ataxic tremor. Action myoclonus may be the principal residual sign of postanoxic encephalopathy, referred to as the Lance-Adams syndrome and discussed further in Chap. 39. It has been proposed that this condition has a cerebellar origin. Myoclonus is described more fully in Chap. 4, where it is pointed out that it more often has its origin in diseases of the cerebral cortex.


Neurology_Adams

Neurology_Adams. In addition to its motor functions, it has been established that the cerebellum participates in certain aspects of cognitive function and behavior (see the reviews by Schmahmann and Sherman and by Leiner et al). These authors have described a wide range of subtle alterations of memory and cognition, language function, and behavior in patients with disease apparently limited to the cerebellum (as determined by CT and MRI). However, it is not entirely clear if there is a uniform clinical pathologic syndrome in which a distinctive group of cognitive–behavioral deficits are related to a cerebellar lesions. These recent investigations into the cerebral influences of the cerebellum are accurate and novel contributions to neurology, but at the same time, the changes referred to are subtle in the bedside neurologic examination. Rarely, as in a patient under our care, a recovered aphasia from a prior cerebral infarct was unmasked by an acute cerebellar stroke. Slowly developing cerebellar


Neurology_Adams

Neurology_Adams. the bedside neurologic examination. Rarely, as in a patient under our care, a recovered aphasia from a prior cerebral infarct was unmasked by an acute cerebellar stroke. Slowly developing cerebellar disorders, such as tumors, do not appear to demonstrate this phenomenon.


Neurology_Adams

Neurology_Adams. Noncerebellar Sources of Ataxia Ataxia has a distinct appearance to the examiner and is even identifiable by lay persons as wildly erratic movements. However, several clinical abnormalities simulate the incoordination of ataxia, among them myoclonus, spasticity, convulsions, tics, tremors of various types, and psychogenic movement disorders.


Neurology_Adams

Neurology_Adams. Furthermore, diseases other than those of the cerebellum can cause ataxia that closely simulates the cerebellar type. The ataxia of severe sensory neuropathy and of posterior column or posterior spinal root disease (sensory ataxia) simulates cerebellar ataxia; presumably this is a result of involvement of the large peripheral spinocerebellar afferent fibers. Tabes dorsalis and sensory ganglionopathy are prime examples of this type of disorder. However, there should seldom be difficulty in separating cerebellar from sensory ataxia if one takes note of the loss of distal joint position sense, absence of associated cerebellar signs such as dysarthria or nystagmus, loss of tendon reflexes, and the corrective effects of vision on sensory ataxia. In peripheral neuropathy and in spinal cord disease with ataxia, the Romberg sign is invariably present, reflecting a parallel dysfunction of large afferent fibers in the posterior columns; this sign is not found in lesions of the cerebellar


Neurology_Adams

Neurology_Adams. disease with ataxia, the Romberg sign is invariably present, reflecting a parallel dysfunction of large afferent fibers in the posterior columns; this sign is not found in lesions of the cerebellar hemispheres except that the patient may initially sway with eyes open, and a bit more with eyes closed.


Neurology_Adams

Neurology_Adams. A cerebellar type of tremor reaches an extreme form in the large-fiber polyneuropathy related to antibodies against myelin-associated glycoprotein but the features are closer to an enhanced action tremor, as discussed in Chap. 43. In the Miller Fisher syndrome, which is considered to be a version of acute Guillain-Barré polyneuropathy, sensation is intact or affected only slightly and the severe ataxia and intention tremor are presumably a result of a selective peripheral disorder of spinocerebellar nerve fibers. Disorders of these same fibers in the spinocerebellar tracts of the cord may produce similar sensory-ataxic effects; subacute compressive lesions such as thoracic meningioma or demyelinating lesions are the usual causes. Again, there is a prominent Romberg sign. Occasionally, a cerebellar-like tremor in one limb results from a lesion in the dorsolateral cord or roots that selectively interrupts afferent fibers, presumably those directed to the spinocerebellar tracts.


Neurology_Adams

Neurology_Adams. Intense vertigo produces a special ataxia of gait and that is distinguished by reeling from side-to-side and listing to one side, past pointing, and torsional-rotatory nystagmus, as discussed in Chap. 14. The nonvertiginous ataxia of gait caused by vestibular paresis (e.g., streptomycin toxicity) has special qualities, which are described in Chap. 6. Vertigo and cerebellar ataxia may be concurrent, as in some patients with a paraneoplastic disease and in those with infarction of the lateral medulla and inferior cerebellum. An unusual and transient ataxia of the contralateral limbs occurs acutely after infarction or hemorrhage in the anterior thalamus (thalamic ataxia); in addition to characteristic signs of thalamic damage, there may be an accompanying unilateral asterixis. Finally, a lesion of the superior parietal lobule (areas 5 and 7 of Brodmann) rarely results in mild ataxia of the contralateral limbs. Differential Diagnosis of Cerebellar Disease


Neurology_Adams

Neurology_Adams. In the diagnosis of disorders characterized by generalized cerebellar ataxia (affecting limbs, gait, and speech), the mode of onset, rate of development, and degree of permanence of the ataxia are of particular importance, as summarized in Table 5-3. Unilateral ataxia without accompanying signs is most often caused by infarction or tumor in the ipsilateral cerebellar hemisphere or by demyelinating disease affecting cerebellar connections to the brainstem. Each of the major causes is discussed in an appropriate chapter. In adults, toxic effects of medications, paraneoplastic, and demyelinating cases account for the largest proportion of cases of subacute onset, and hereditary forms are the usual cause of very slowly progressive and chronic ones, particularly if gait is predominantly affected. The last category of genetic ataxias constitutes a large and heterogeneous group for which the mutation has been established in many cases; they are described in Chap. 38.


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Neurology_Adams. Allen GI, Tsukahara N: Cerebrocerebellar communication systems. Physiol Rev 54:957, 1974. Babinski J: De l’asynergie cerebelleuse. Rev Neurol 7:806, 1899. Chambers WW, Sprague JM: Functional localization in the cerebellum. I. Organization in longitudinal cortico-nuclear zones and their contribution to the control of posture, both extrapyramidal and pyramidal. J Comp Neurol 103:104, 1955. Chambers WW, Sprague JM: Functional localization in the cerebellum. II. Somatotopic organization in cortex and nuclei. AMA Arch Neurol Psychiatry 74:653, 1955. Diener HC, Dichgans J: Pathophysiology of cerebellar ataxia. Mov Disord 7:95, 1992. Evarts EV, Thach WT: Motor mechanism of the CNS: cerebrocerebellar interrelations. Annu Rev Physiol 31:451, 1969. Gilman S, Bloedel J, Lechtenberg R: Disorders of the Cerebellum. Philadelphia, Davis, 1980, pp 159–177. Hallett M, Berardelli A, Matheson J, et al: Physiological analysis of simple rapid movement in patients with cerebellar deficits.


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Neurology_Adams. Hallett M, Berardelli A, Matheson J, et al: Physiological analysis of simple rapid movement in patients with cerebellar deficits. J Neurol Neurosurg Psychiatry 54:124, 1991. Hallett M, Shahani BT, Young RR: EMG analysis of patients with cerebellar deficits. J Neurol Neurosurg Psychiatry 38:1163, 1975. Holmes G: The cerebellum of man: Hughlings Jackson Lecture. Brain 62:1, 1939. Jansen J, Brodal A: Aspects of Cerebellar Anatomy. Oslo, Johan Grundt Tanum Forlag, 1954. Kandel ER, Schwartz JH, Jessel TM (eds): Principles of Neural Science, 4th ed. New York, McGraw-Hill, 2000. Leiner HC, Leiner AL, Dow RS: Does the cerebellum contribute to mental skills? Behav Neurosci 100:443, 1986. Manni E, Petrosini L: A century of cerebellar somatotopy: a debated representation. Nature Rev 5:241, 2004. Schmahmann JD, Sherman JC: The cerebellar cognitive affective syndrome. Brain 121:561, 1998.


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Neurology_Adams. Schmahmann JD, Sherman JC: The cerebellar cognitive affective syndrome. Brain 121:561, 1998. Sprague JM, Chambers WW: Control of posture by reticular formation and cerebellum in the intact, anesthetized and unanesthetized and in the decerebrated cat. Am J Physiol 176:52, 1954. Stewart TG, Holmes G: Symptomatology of cerebellar tumors: A study of forty cases. Brain 27:522, 1904. Thach WT Jr, Goodkin HP, Keating JG: The cerebellum and the adaptive coordination of movement. Annu Rev Neurosci 150:403, 1992. Thach WT Jr, Montgomery EB Jr: Motor system. In: Pearlman AL, Collins RC (eds): Neurobiology of Disease. New York, Oxford University Press, 1992, pp 168–196. Urban PP, Marx J, Hunsche S, et al: Cerebellar speech representation. Arch Neurol 60:965, 2003.


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Neurology_Adams. Urban PP, Marx J, Hunsche S, et al: Cerebellar speech representation. Arch Neurol 60:965, 2003. Figure 5-1. Overview of anatomical and functional organization of the cerebellum. A. Dorsal view of the cerebellum showing midline vermis, lateral hemispheres, and the deep nuclei. B. Midsagittal view of the brainstem and cerebellum. C. Ventral view of the cerebellum. D. Functional zones of the cerebellum. (Redrawn and modified with permission from Kandel ER, Schwartz JH, Jessel TM, et al: Principles of Neural Science, 5th ed. New York, McGraw-Hill, 2013.) Figure 5-2. Coronal T1-weighted MRI showing the relationship between the fourth ventricle and cerebellar peduncles.


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Neurology_Adams. Figure 5-2. Coronal T1-weighted MRI showing the relationship between the fourth ventricle and cerebellar peduncles. Figure 5-3. Cerebellar projections to the red nucleus, thalamus, and cerebral cortex. Ascending tracts are red and descending tracts are blue. Note that all efferent fibers leaving the cerebellum exit through the superior cerebellar peduncle. (Adapted with permission from House EL et al: A Systematic Approach to Neuroscience, 3rd ed. New York, McGraw-Hill, 1979.) Figure 5-4. The Guillain-Mollaret triangle connecting the red nucleus, inferior olive, and contralateral dentate nucleus.


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Neurology_Adams. Figure 5-4. The Guillain-Mollaret triangle connecting the red nucleus, inferior olive, and contralateral dentate nucleus. Figure 5-5. Anatomic organization of the cerebellar cortex in a longitudinal and transverse section of a folium. Shown are the relationships between (a) climbing fibers and Purkinje cells, (b) mossy fibers and both granule cells and Golgi cells, and (c) the parallel fibers that course longitudinally and connect these three main cell types. (Reproduced with permission from Kandel ER, Schwartz JH, Jessel TM, et al: Principles of Neural Science, 5th ed. New York, McGraw-Hill, 2013.)


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Neurology_Adams. Figure 5-6. The physiologic organization of the cerebellum. The main input into the cerebellum is via mossy fibers from various sources and via climbing fibers from the contralateral inferior olive. Both are excitatory. Mossy fibers synapse on granule cells, whose axons form the parallel fibers in the molecular layer. These axons synapse with Purkinje cells and also with stellate and basket cells that inhibit nearby Purkinje cells. Further modulation occurs via a recurrent loop made by Golgi cells, whose dendrites lie in the molecular layer and whose axons synapse on granule cells. Output from the cerebellar cortex has an inhibitory effect on the deep cerebellar nuclei. This output is modulated by climbing fibers that synapse directly on Purkinje cell dendrites. (Adapted with permission from Eccles JC, Llinas R, Sasaki K: Intracellularly recorded responses of the cerebellar Purkinje cells. Exp Brain Res 1:161, 1966.) Chapter 5 Ataxia and Disorders of Cerebellar Function


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Neurology_Adams. Chapter 5 Ataxia and Disorders of Cerebellar Function Disorders of Stance and Gait It is interesting to consider that man’s bipedal gait is unique among animals. The transition from quadripedal to bipedal gait created challenges for the nervous system in maintaining upright posture, stability when standing, and a complex righting reflex to avoid falls. A considerable amount of the cerebra is devoted to integrating the visual, proprioceptive, and vestibular, information that drive the cortical, spinal, cerebellar, and basal ganglionic motor activities of gait.


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Neurology_Adams. The analysis of stance, carriage, and gait is a rewarding exercise; with some experience, the examiner can sometimes reach a neurologic diagnosis merely by noting the manner in which the patient enters the office. Considering the frequency of falls that result from gait disorders and their consequences such as hip fracture, and the resultant need for hospital and nursing home care, gait abnormalities are an important subject for all physicians. The substantial dimensions of the social and economic problem of falls and the elderly have been described by Tinetti and Williams.


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Neurology_Adams. Certain diseases that affect motor and sensory function manifest themselves most clearly as impairments of stance and locomotion; their evaluation depends on knowledge of the neural mechanisms underlying the uniquely human function of standing and bipedal walking. As important in neurology are the myriad ways that gait can be disordered without implicating any of the elemental aspects of neurologic function; in these, the integrative mechanisms for stable walking and avoidance of falls are affected. Moreover, especially in the elderly, problems with gait and balance are due to two or more disorders and even to ageing itself.


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Neurology_Adams. Gait varies considerably from one to another and it is a commonplace observation that a person may be identified by the sound of his footsteps, notably the pace and the lightness or heaviness of tread, by their carriage at a distance, even before the person is recognizable by face. Obviously, the gaits of men and women differ, a woman’s steps being quicker and shorter. Sherlock Holmes expressed pride in his talent for deducing from the manner of gait, an individual’s personality and occupation. It is said that Charcot could often make the correct diagnosis, even before seeing the patient, based on the sound of patient walking down the hallway on the way to the examining room. The changes in stance and gait that accompany aging—the slightly stooped posture and slow, stiff tread as described in Chap. 28, on aging—are so familiar that they are not perceived as abnormalities.


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Neurology_Adams. The normal gait seldom attracts attention but it should be observed with care if slight deviations from normal are to be appreciated. The body is erect, the head is straight, and the arms hang loosely and gracefully at the sides, each moving rhythmically forward with the opposite leg. The feet are slightly externally rotated, the steps are approximately equal, and the medial malleoli almost touch as each foot passes the other. The medial edges of the heels, as they strike the ground with each step, lie almost along a straight line. As each leg moves forward, there is coordinated flexion of the hip and knee, dorsiflexion of the foot, and a barely perceptible elevation of the hip, so that the foot clears the ground. Also, with each step, the thorax advances slightly on the side opposite the swinging lower limb. The heel strikes the ground first, and inspection of the shoes will show that this part is most subject to wear.


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Neurology_Adams. The normal gait cycle, defined as the period between successive points at which the heel of the same foot strikes the ground, is illustrated in Fig. 6-1, based on the studies of Murray and coworkers, and of Olsson. In this figure, the cycle is initiated by the heel strike of the right foot. The stance phase, during which one foot is in contact with the ground, occupies 60 to 65 percent of the cycle. The swing phase begins when the left toes leave the ground. For 20 to 25 percent of the walking cycle, both feet are in contact with the ground (double-limb support). In later life, when the steps shorten and the cadence (the rhythm and number of steps per minute) decreases, the proportion of double-limb support increases (see further on). Surface electromyograms show an alternating pattern of activity in the legs, predominating in the flexors during the swing phase and in the extensors during the stance phase.


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Neurology_Adams. When analyzed in greater detail, the requirements for locomotion in an upright, bipedal position may be reduced to the following elements: (1) antigravity support of the body, (2) stepping, (3) the maintenance of equilibrium, and (4) a means of propulsion. Locomotion is impaired in the course of neurologic disease when one or more of these mechanical principles are prevented from operating normally.


Neurology_Adams

Neurology_Adams. The muscles of greatest importance in maintaining the erect posture are the erector spinae and the extensors of the hips and knees. The upright support of the body is provided by righting and antigravity reflexes, which allow a person to arise from a lying or sitting position to an upright bipedal stance and to maintain firm extension of the knees, hips, and back, modifiable by the position of the head and neck. These postural reflexes depend on the afferent vestibular, somatosensory (proprioceptive and tactile), and visual impulses, which are integrated in the spinal cord, brainstem, and basal ganglia. Transection of the neuraxis between the red and vestibular nuclei leads to exaggeration of these antigravity reflexes—decerebrate rigidity.


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Neurology_Adams. Stepping, the second element of the gait cycle, is a basic movement pattern present at birth and integrated at the spinal, midbrain, and diencephalic levels. It is elicited by contact of the sole with a flat surface and a shifting of the center of gravity—first laterally onto one foot, allowing the other to be raised, and then forward, allowing the body to move onto the advancing foot. Rhythmic stepping movements can be initiated and sustained in decerebrate or “spinal” cats and dogs. This is accomplished in animals through the activity of interneurons that are organized as rhythmic “locomotor generators,” akin to the pattern generators that permit the rhythmic movement of wings or fins. There is no clear evidence for a similar system of locomotor control in monkeys or humans. There are poorly localized spinal mechanisms for walking in man but they cannot produce the act of walking and they require descending control from vaguely defined higher centers. These higher areas are located


Neurology_Adams

Neurology_Adams. localized spinal mechanisms for walking in man but they cannot produce the act of walking and they require descending control from vaguely defined higher centers. These higher areas are located in the caudal midbrain tegmentum and pontine reticular formation (in or near the pediculopontine nucleus); they control the spinal gait mechanisms through the reticulospinal, vestibulospinal, and tectospinal pathways in the ventral cord (see Eidelberg and colleagues and Lawrence and Kuypers).


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Neurology_Adams. Moreover, these brainstem locomotor regions are activated by frontal cortical areas that are absolutely integral to initiating and engaging the gait cycle. Although a discrete “gait center” cannot be found in the cerebrum, frontal lesions can devastate gait as discussed further on. Often, the supplementary motor areas relating to the legs (superior frontal gyri on both sides) or periventricular white matter are implicated. In all likelihood, the medial frontal lobes embody automatic programs for walking that are intimately tied to adjacent networks in the striatum.


Neurology_Adams

Neurology_Adams. Equilibrium involves the maintenance of balance in relation to gravity and to the direction of movement in order to retain a vertical posture. The unstable center of gravity that prevails in walking must shift within narrow limits from side to side and forward as the weight is borne first on one foot, then on the other. This is accomplished through the activity of highly sensitive postural and righting reflexes that have both peripheral (stretch reflexes) and central (vestibulocerebellar reflexes) components. These reflexes are activated within 100 ms of each shift in the support surface and require reliable afferent information from the visual, vestibular, and proprioceptive systems.


Neurology_Adams

Neurology_Adams. Propulsion is provided by leaning forward and slightly to one side and permitting the body to fall a certain distance before being checked by the support of the leg. Here, both forward and alternating lateral movements must occur. In contrast to walking, running requires that both feet are momentarily off the ground, necessitating a forward drive or thrust by the trailing leg. Because normal body posture and locomotion require intact vestibular function, proprioception, and vision (we see where we are going and adjust our steps), the effects of deficits in these senses are worth noting. A blind person—or a normal one who is blindfolded or walks in the dark—moves cautiously, with arms slightly forward to avoid collisions, and shortens his step slightly on a smooth surface; there is less rocking of the body and the gait is unnaturally stiff and cautious.


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Neurology_Adams. Pain in the hips or knees can lead to a disorder (antalgic gait) that can be challenging to distinguish from neurological causes of gait problems. Slowness of the swing phase and reduction in the amount of time spent with the painful limb in contact with the ground may be clues to recognizing rheumatological and orthopedic causes of a gait disorder. Of course, the patient’s description of pain in certain positions or actions makes the problem self-evident and maneuvers, such as passive moving the leg about the hip, further expose the source of gait disruption. At times, musculoskeletal disorders produce little pain but alter the gait pattern as a result of protective and compensatory responses. Weakness of one or a group of adjacent muscles impart a peculiar but identifiable appearance to walking, some aspects of which are detailed further on. Examination of the Patient With Abnormal Gait


Neurology_Adams

Neurology_Adams. Examination of the Patient With Abnormal Gait When confronted with a disorder of gait, the examiner should observe the patient’s stance and the positions of the legs, trunk, and arms, and their interrelationships. It is good practice to watch patients as they enter the examining room, when they are apt to walk more naturally than during the performance of commanded tasks. Walking without the support of a cane or the arm of a companion brings out a certain stiffness of the legs and firmness of the muscles.


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Neurology_Adams. The patient should be asked to walk, noting in particular any hesitation in starting and negotiating turns, width of base, length of stride, foot clearance, arm swing, and cadence. More delicate tests of gait are walking a straight line heel to toe (“tandem walking test”), walking backward, and having the patient arise quickly from a chair, walk briskly, stop and turn suddenly, walk back, and sit down again. A tendency to veer to one side, as occurs with unilateral cerebellar or vestibular disease, can be elicited by having the patient walk around a chair. When the affected side is toward the chair, the patient tends to walk into it; when it is away from the chair, there is a veering outward in ever-widening circles. Turning the patient three full revolutions with eyes open, first right and then left, each time followed by asking the patient to walk naturally, allows the examiner to stress the vestibular apparatus and to compare the two sides. The patient affected by a vestibular or


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Neurology_Adams. and then left, each time followed by asking the patient to walk naturally, allows the examiner to stress the vestibular apparatus and to compare the two sides. The patient affected by a vestibular or cerebellar process will veer to the side of a lesion. Marching in place with eyes closed (Unterberger, or Fukada stepping tests) also reveals a rotation in the yaw plane (rotation around the vertical axis), indicating an asymmetrical disorder in the plane of the horizontal semicircular ducts or their connections. Spasticity of one or both legs can be detected as stiffness and delay in moving the leg forward and a tendency to trace an arc with the toe, which gives rise to a scraping sound on the floor and wearing of the toe of the shoe.


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Neurology_Adams. The patient should be asked to stand with feet together and head erect, with eyes open and then closed (Romberg test). A normal person can stand with feet together and eyes closed while moving the head from side to side, a test that blocks both visual and vestibular cues and induces certain compensatory trunk and leg movements that depend solely on proprioceptive afferent mechanisms (Ropper). As mentioned in Chapter 5, the Romberg sign—marked swaying or falling with the eyes closed but not with the eyes open—usually indicates a loss of postural sense, not of cerebellar function, although with vestibular or cerebellar disease there may be an exaggeration of swaying. Swaying due to psychological causes may be uncovered by noting that balance is improved when distracting the patient, for example, by asking him to look at the ceiling or follow the examiner’s finger, or to touch the tip of his nose alternately with the forefinger of one hand and then the other.


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Neurology_Adams. It is then instructive to observe the patient’s postural reaction to a sudden push or tug at the shoulders, backward, and forward, or to the side. With postural instability of any type there is a delay or inadequacy of corrective actions. The patient may be asked to hop on one leg and to jog. Finally, it may be useful to have the patients simulate walking while seated or in bed. A dissociation between the inability to walk and the retained ability to simulate walking when not erect may reveal a disorder of the integrative mechanisms for gait in the frontal lobe or other regions. Together, these tests serve to distinguish whether a disordered gait is due to a proprioceptive, labyrinthine-vestibular, basal ganglionic, corticospinal, or cerebellar mechanism. It is then necessary to determine which of several other disturbances of function is responsible for the patient’s disorder of gait, for example, the antalgic gait referred to earlier.


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Neurology_Adams. The following types of abnormal gait (Table 6-1) are distinctive enough that, with experience, they can be readily identified. Cerebellar Gait (See Also Chap. 5) The main features are a wide base (separation of legs), unsteadiness, irregularity of steps, and lateral veering. Steps are uncertain, some are shorter and others longer than intended and the patient may compensate for these abnormalities by shortening his steps or even keeping both feet on the ground simultaneously. Cerebellar gait is sometimes referred to as “reeling” or “drunken,” but these terms are not entirely correct and are characteristic instead of intoxication and of certain types of labyrinthine disease, as explained further on.


Neurology_Adams

Neurology_Adams. With cerebellar ataxia, the unsteadiness and irregular swaying of the trunk are prominent when the patient arises from a chair or turns suddenly while walking and may be evident when he has to stop walking abruptly and sit down; it may be necessary to grasp the chair for support. Cerebellar ataxia may be so severe that the patient cannot sit without swaying. If it is less severe, standing with feet together and head erect is difficult with open eyes and only slightly more so with eyes closed. In its mildest form, ataxia is best demonstrated by having the patient walk a line heel to toe; after a step or two, he loses his balance and finds it necessary to place one foot to the side to avoid falling. Elderly individuals may be expected to have difficulty with the task.


Neurology_Adams

Neurology_Adams. As just stated, the patient with cerebellar ataxia who sways perceptibly when standing with feet together and eyes open, will sway somewhat more with eyes closed. This slight increase in swaying may be misattributed to loss of proprioceptive input to the cerebellum. By contrast, removal of visual clues from a patient with proprioceptive loss causes a marked increase in swaying or falling (the Romberg sign). Thus, the defect in cerebellar disease is primarily in the coordination of the sensory input from proprioceptive, labyrinthine, and visual information with reflex movements, particularly those that are required to make rapid adjustments to changes in posture and position. This integrative deficiency is also reflected in the stepping test, in which the patient is asked to march on the spot with eyes closed. Those with vestibular and sometimes unilateral cerebellar disease have difficulty remaining stable and have a tendency to turn to the left or right or to move forward


Neurology_Adams

Neurology_Adams. on the spot with eyes closed. Those with vestibular and sometimes unilateral cerebellar disease have difficulty remaining stable and have a tendency to turn to the left or right or to move forward (occasionally backward) after 5 or 10 steps.


Neurology_Adams

Neurology_Adams. Cerebellar abnormalities of stance and gait are usually accompanied by signs of incoordination of the legs, but they need not be. The presence of ataxia of the legs depends on involvement of the cerebellar hemispheres as distinct from the anterosuperior (vermian) midline structures that dominate in the control of gait as described in Chap. 5. This emphasizes the value of having the patient get out of bed and walk, rather than depending solely on an examination for ataxia of the legs while the patient remains in bed. If the cerebellar lesions are bilateral, there is often titubation (tremor) of the head and trunk. Cerebellar gait is seen most commonly in patients with multiple sclerosis, cerebellar tumors (particularly those affecting the vermis—e.g., medulloblastoma), cerebellar stroke, paraneoplastic cerebellar syndrome, and prominently, in the large group of cerebellar degenerations. Reeling Gait of Intoxication


Neurology_Adams

Neurology_Adams. This is characteristic of inebriation with alcohol, sedative drugs, and antiepileptic drugs. The drunken patient totters, reels, tips forward and then backward, appearing each moment to be on the verge of losing his balance and falling. Control over the trunk and legs are greatly impaired. The steps are irregular and uncertain. Such patients may appear indifferent to the quality of their performance, but under certain circumstances they can momentarily correct the defect. As indicated above, the adjectives drunken and reeling are used frequently to describe the gait of cerebellar disease, but the similarities between them are only superficial. The severely intoxicated patient reels or sways in many different directions and seemingly makes little or no effort to correct the staggering by watching his legs or the ground, as occurs in cerebellar or sensory ataxia. Also, the variability of the drunken gait is noteworthy. Despite wide excursions of the body and deviation from the line of


Neurology_Adams

Neurology_Adams. watching his legs or the ground, as occurs in cerebellar or sensory ataxia. Also, the variability of the drunken gait is noteworthy. Despite wide excursions of the body and deviation from the line of march, the drunken patient may, for short distances, be able to walk on a narrow base and maintain his balance. In contrast, the patient with cerebellar gait has great difficulty in correcting his balance if he sways or lurches too far to one side. Milder degrees of the drunken gait resemble the gait disorder that follows loss of labyrinthine function discussed below.


Neurology_Adams

Gait Disorder of Vestibulopathy

Neurology_Adams. Gait Disorder of Vestibulopathy


Neurology_Adams

Neurology_Adams. Patients with a chronic vestibulopathy show unsteadiness in standing and walking, often without widening their base, and an inability to descend stairs without holding onto the banister. They complain of a particular type of imbalance, usually with movement but at times when standing still—a sensation that may be likened to being on the deck of a rolling ship (mal de barquement). Running and turning quickly are even more impaired, with lurching in all directions. The patient has great difficulty in focusing his vision on a fixed target when he is moving or on a moving target when he is either stationary or moving. When the body is in motion or the head is moved suddenly, objects in the environment may appear momentarily blurred or actually jiggle up and down or from side to side (oscillopsia). Driving a car or reading on a train is difficult or impossible; even when walking, the patient may need to stop in order to read a sign. These abnormalities indicate a loss of stabilization of


Neurology_Adams

Neurology_Adams. Driving a car or reading on a train is difficult or impossible; even when walking, the patient may need to stop in order to read a sign. These abnormalities indicate a loss of stabilization of ocular fixation by the vestibular system during body movements (the vestibular-ocular reflex, or VOR). An elderly person has difficulty compensating for these abnormalities. Proof that the gait of such persons with vestibulopathy is dependent on visual clues comes from their performance blindfolded or in the dark, when their unsteadiness and staggering increase to the point of falling. When standing with eyes closed, they sway more than normal but generally do not fall over (i.e., they do not have a Romberg sign). The diagnosis is confirmed by testing labyrinthine function (caloric and rotational testing, electronystagmography, and posture platform testing).


Neurology_Adams

Neurology_Adams. Chronic disorders of vestibular function in relation to gait disorders are most often the result of prolonged administration of aminoglycoside antibiotics or other toxic medications, which destroy the hair cells of the vestibular labyrinth. Vestibular suppressants, such as meclizine and similar medications, mostly anticholinergic and antihistaminic that are available over the counter, can lead to decreased function of the vestibular system, with a persistent gait disorder if used for more than a few weeks. This also occurs in some patients in the late stages of Ménière disease and, infrequently, for no definable reason. A colorful essay by a physician depicting the effects of the loss of the vestibular apparatus can be found by the author “JC” in the New England Journal of Medicine.


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Neurology_Adams. The literature is also replete with references to a “multimodal” gait disorder in the elderly that is the result of an ostensible aging of the vestibular organ, together with impaired proprioceptive function caused by distal neuropathy in the elderly, and impaired vision. Toppling, meaning tottering and falling, occurs with brainstem and cerebellar lesions, especially in the older person following a stroke. In a related defect caused by a vestibular disorder, the patient may describe a sense of being pushed (pulsion) rather than of imbalance.


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Neurology_Adams. With midbrain strokes, toppling falls tend to be backward (retropulsion). In patients with progressive supranuclear palsy (discussed in Chap. 38), where dystonia of the neck is combined with paralysis of vertical gaze and pseudobulbar features, unexplained unanticipated toppling is an early and prominent feature. The falls of progressive supranuclear palsy may derive from a disorder of the righting mechanism. In midbrain disease, including progressive supranuclear palsy, a remarkable feature is the lack of appreciation of a sense of imbalance. Toppling to one side is a feature of the lateral medullary syndrome, usually from infarction.


Neurology_Adams

Neurology_Adams. In the advanced stages of Parkinson disease, falling of a similar type may be a serious problem, but it is more surprising how relatively infrequently it occurs. The cause of the toppling phenomenon is unclear; it does not have its basis in weakness, ataxia, or loss of deep sensation. It appears to be a disorder of balance that is occasioned by precipitant action or the wrong placement of a foot and by a failure of the righting reflexes. Slowness of motor response is another factor. Sensory (Tabetic, or Proprioceptive) Gait Ataxia


Neurology_Adams

Neurology_Adams. A loss of proprioception—as occurs in patients with severe large-fiber polyneuropathy, posterior nerve root lesions (e.g., tabes dorsalis, lumbosacral root compression), or interruption of the posterior columns in the spinal cord (multiple sclerosis, vitamin B12 deficiency, spondylotic, or tumor compression)—abolishes or seriously impairs the capacity for independent locomotion. After years of training, such patients still have difficulty in initiating gait and in forward propulsion. As J. Purdon Martin described in the severe form of the disorder, they hold their hands slightly in front of the body, bend the body and head forward, walk with a wide base and irregular, uneven steps, but still rock the body. If they are tilted to one side, they fail to compensate for their abnormal posture. If they fall, they cannot rise without help; they are sometimes unable to crawl or to get into an “all fours” posture. They have difficulty in getting up from a chair. When standing, if instructed to


Neurology_Adams

Neurology_Adams. If they fall, they cannot rise without help; they are sometimes unable to crawl or to get into an “all fours” posture. They have difficulty in getting up from a chair. When standing, if instructed to close their eyes, they sway markedly and fall (Romberg sign).


Neurology_Adams

Neurology_Adams. The principal observable features of sensory-ataxic gait are the brusqueness of movement of the legs and in its extreme, stamping of the feet as the foot is forcibly brought down onto the floor (apparently to detect the location of the foot as a substitute for proprioception). The feet are placed far apart to correct the instability, and patients carefully watch both the ground and their legs. As they step out, their legs are flung abruptly forward and outward, in irregular steps of variable length and height. The body is held in a slightly flexed position, and some of the weight is supported on the cane that the severely ataxic patient usually carries. To use Ramsay Hunt’s characterization, the patient with this gait disorder is recognized by his “stamp and stick.” As mentioned, the most specific feature is that the ataxia is markedly exaggerated when the patient is deprived of visual cues, as in walking in the dark. Such patients, when asked to stand with feet together and eyes


Neurology_Adams

Neurology_Adams. most specific feature is that the ataxia is markedly exaggerated when the patient is deprived of visual cues, as in walking in the dark. Such patients, when asked to stand with feet together and eyes closed, show greatly increased swaying and usually, the fully expressed Romberg sign with falling off to one side. It is said that in cases of sensory ataxia, the shoes do not show wear in any one place because the entire sole strikes the ground at once. Examination usually discloses a loss of position sense in the feet and legs and usually of vibratory sense as well. The peripheral or central location of the sensory lesions can be further determined by the state of the tendon reflexes.


Neurology_Adams

Neurology_Adams. Whatever the location of the lesion, its effect is to deprive the patient of perception of the position of his limbs and, more relevant to gait, to interfere with a large amount of afferent proprioceptive and related information that does not attain conscious perception. A sense of imbalance is usually present but these patients do not describe dizziness. They are aware that the trouble is in the legs and not in the head, that foot placement is awkward, and that the ability to recover quickly from a misstep is impaired. The resulting disorder is characterized by varying degrees of difficulty in standing and walking; in advanced cases, there is a complete failure of locomotion, although muscular power is retained.


Neurology_Adams

Neurology_Adams. Formerly, a disordered gait of this type was observed most frequently with tabes dorsalis, hence the term tabetic gait; but it is also seen in Friedreich ataxia and related forms of spinocerebellar degeneration, subacute combined degeneration of the spinal cord (vitamin B12 deficiency), a large number of sensory polyneuropathies, sensory ganglionopathies of various causes, and those cases of multiple sclerosis or compression of the spinal cord in which the posterior columns are involved.


Neurology_Adams

Neurology_Adams. This gait pattern is caused by paralysis of the pretibial and peroneal muscles, with resultant inability to dorsiflex the foot (foot drop). The steps are regular and even, but the advancing foot hangs with the toes pointing toward the ground. In its purest form, it is the result of peroneal nerve or fifth lumbar root damage. Walking is accomplished by excessive flexion at the hip, the leg being lifted abnormally high in order for the foot to clear the ground. There is a slapping noise as the foot strikes the floor. Thus there is a superficial similarity to the tabetic gait described just above, especially in cases of severe polyneuropathy, where the features of steppage and sensory ataxia may be combined. However, patients with steppage gait alone are not troubled by a perception of imbalance; they fall from tripping on carpet edges and curbstones.


Neurology_Adams

Neurology_Adams. Foot drop may be unilateral or bilateral and occurs in diseases that affect the peripheral nerves of the legs or motor neurons in the spinal cord, lumbar roots, such as chronic acquired neuropathies (diabetic, inflammatory, toxic, and nutritional), Charcot-Marie-Tooth disease (peroneal muscular atrophy), progressive spinal muscular atrophy, and poliomyelitis. It may also be observed in certain types of muscular dystrophy in which the distal musculature of the limbs is involved.


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Neurology_Adams. A particular disorder of gait, also of peripheral origin and resembling steppage gait, may be observed in patients with painful dysesthesias of the soles of the feet. Because of the exquisite pain evoked by tactile stimulation of the feet, the patient treads gingerly, as though walking barefoot on hot sand or pavement, with the feet rotated in such a way as to limit contact with their most painful portions. The usual cause is one of the painful peripheral neuropathies (most often alcoholic-nutritional but also toxic and amyloid types), causalgia, or erythromelalgia.


Neurology_Adams

Neurology_Adams. The patient with hemiplegia or hemiparesis holds the affected leg stiffly and does not flex it freely at the hip, knee, and ankle. The leg tends to rotate outward to describe a semicircle, first away from and then toward the trunk (circumduction). The foot scrapes the floor, contact being made by the toe and outer heel of the foot. One can recognize a spastic gait by the sound of slow, rhythmic scuffing of the foot and wearing of the medial toe of the shoe. With a cerebral or cervical lesion, the arm on the affected side is weak and stiff to a variable degree; it is carried in a flexed position and does not swing naturally (Fig. 6-2A). In the hemiparetic child, the arm tends to abduct as he steps forward. This type of gait disorder is most often a sequela of stroke or trauma but may result from any condition that damages the corticospinal pathway on one side.


Neurology_Adams

Neurology_Adams. The spastic paraplegic or paraparetic gait is, in effect, a bilateral hemiplegic gait. Each leg is advanced slowly and stiffly, with restricted motion at the hips and knees. The legs are extended or slightly bent at the knees and the thighs may be strongly adducted, causing the legs almost to cross as the patient walks (scissor-like gait; Fig. 6-2B). The steps are regular and short and the patient advances only with great effort as though wading waist-deep in water. The defect is in stiffness of the stepping mechanism and in propulsion, not in support or equilibrium.


Neurology_Adams

Neurology_Adams. A spastic paraparetic gait is the major manifestation of cerebral diplegia (Little disease, a type of cerebral palsy), the result of anoxic or other damage to the brain in the perinatal period. This disorder of gait is also seen in a variety of chronic spinal cord diseases involving the dorsolateral and ventral tracts, most often multiple sclerosis, but also including syringomyelia, any type of chronic meningomyelitis, subacute combined system disease of both the pernicious anemia and nonpernicious anemia types, spinal cord compression or traumatic injury, adrenomyeloneuropathy, and familial forms of spastic paraplegia. Frequently in these diseases, the effects of posterior column disease are added, giving rise to a mixed gait disturbance—a spinal spastic ataxia, characteristic of multiple sclerosis and certain spinal cord degenerations such as Friedreich ataxia. (See Also Chap. 38)


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Neurology_Adams. (See Also Chap. 38) With disorders of the basal ganglia, the posture of the body and the postural responses to perturbations in equilibrium are faulty. There is difficulty in taking the first step; once it is taken, and in extreme cases, the body pitches forward and a fall can be prevented only by catch-up stepping (propulsive festination). Similarly, a step backward may induce a series of quickening steps in that direction (retropulsive festination). Corrective righting reflexes are clearly faulty when the patient is pushed off balance (Denny-Brown).


Neurology_Adams

Neurology_Adams. Diminished or absent arm swing, forward bent torso, short or shuffling steps, turning en bloc, hesitation in starting to walk, shuffling, or “freezing” when encountering doorways or other obstacles are the features of the parkinsonian gait. When they are joined to the typical tremor, unblinking and mask-like facial expression, general attitude of flexion, and poverty of movement, there can be little doubt as to the diagnosis (Fig. 6-2C). The arms are carried slightly flexed and ahead of the body and do not swing. The legs are stiff and bent at the knees and hips. The steps are short, and the feet barely clear the ground as the patient shuffles along.


Neurology_Adams

Neurology_Adams. Once walking has started, the upper part of the body advances ahead of the lower part, and the patient is impelled to take increasingly short and rapid steps as though trying to catch up to his center of gravity. The steps become more and more rapid, and the patient could easily break into a trot and collide with an obstacle or fall if not assisted. The term festination derives from the Latin festinare, “to hasten,” and appropriately describes the involuntary acceleration or hastening that characterizes the gait of patients with Parkinson disease. Festination may be apparent when the patient is walking forward or backward. The defects are in rocking the body from side to side, so that the feet can clear the floor, and in moving the legs quickly enough to overtake the center of gravity. The problem is compounded by the inadequacy of postural support reflexes, demonstrable in the standing patient by falling in response to a push against the sternum or a tug backward on the shoulder. A


Neurology_Adams

Neurology_Adams. problem is compounded by the inadequacy of postural support reflexes, demonstrable in the standing patient by falling in response to a push against the sternum or a tug backward on the shoulder. A normal person readily retains his stability or adjusts to modest displacement of the trunk with a single step, but the parkinsonian patient may lean backward with the upper torso and then stagger or fall unless someone stands by to prevent it.


Neurology_Adams

Neurology_Adams. Quite often, one encounters an elderly patient with only the instability and freezing components of the parkinsonian gait disorder, so-called lower-half parkinsonism. Usually, this is not a manifestation of idiopathic Parkinson disease although a few patients are responsive to l-dopa for a brief period. It may be an early manifestation of progressive supranuclear palsy, a basal ganglionic degeneration, normal pressure hydrocephalus, or widespread and frontal subcortical vascular damage as discussed further on, but it also occurs as a virtually isolated phenomenon that progresses independently of other movement disorders or of dementia. The basis is then probably a particular isolated frontal lobe degeneration (see further on). Within a few years, as pointed out by Factor and colleagues in their two papers, the patient is usually reduced to a chair-bound state.


Neurology_Adams

Neurology_Adams. Other very unusual gaits are sometimes observed in Parkinson disease and were particularly prominent in the postencephalitic form, which is now practically extinct. For example, such a patient may be unable to take a step forward or does so only after he takes a few hops or one or two steps backward (aptly mimicked by the Monty Python troupe in their skit, “Ministry of Silly Walks”). Or walking may be initiated by a series of short steps or a series of steps of increasing size. Occasionally such a patient may run better than he walks or walk backward better than forward. Often, walking so preoccupies the patient that talking simultaneously is impossible and requires that the individual must stop to answer a question.


Neurology_Adams

Neurology_Adams. Diseases characterized by involuntary movements and dystonic postures seriously affect gait. In fact, a disturbance of gait may be the initial and dominant manifestation of such diseases, and the testing of gait often brings out abnormalities of movement of the limbs and posture that are otherwise not conspicuous.