Types of chronic pain

1. Why am I having persistent pain? Why doesn't it go away like pain after a paper cut or muscle sprain? 

Most of the time pain goes away after an injury heals. However, if pain persists more than a month or two, it can become chronic pain. Sometimes pain becomes chronic because the underlying problem does not heal. For instance, arthritis causes long term inflammation and damage to the joints, and it may hurt as long as the inflammation lasts. Unfortunately, chronic pain may also occur despite healing and with no obvious injury to tissues. This may be the result of damage to the nerves that transmit pain (neuropathic pain), but chronic pain also affects the entire nervous system, sometimes in a permanent way. When any type of pain lasts a long time there can be changes in the spinal cord and the brain that change how we perceive painful sensations. These changes may result in severe pain with little or no painful stimulus. Some chronic pain can be very difficult to treat and can become so frustrating for patients that it is often accompanied by depression or other emotional problems. It is this type of pain that represents some of the most challenging problems a pain management specialist can face.

2. What is neuropathic pain and how is it different from musculoskeletal pain (like a muscle sprain)?

We usually think of pain in terms of an injury or inflammation. This pain can serve a useful purpose, because when we are hurt we also protect ourselves to allow healing and to prevent further injury. Neuropathic pain, on the other hand, has no benefit. It occurs because of abnormal function of the nervous system. This includes a wide variety of disorders affecting any part of the nervous system from the brain to the spinal cord to the smallest nerves in the toes. In some cases, pain sensation fibers send a signal even if there is no painful stimulus. In other cases, sensory signals get crossed and "misread" as pain. A stroke can leave a patient unable to process sensation properly. And sometimes, the parts of our nervous system that help us manage pain stop working.

3. What are some neuropathic pain syndromes? 

There are many types of neuropathic pain. Some of the more common syndromes are diabetic neuropathy, shingles and post herpetic neuralgia, painful scars (neuromas), phantom limb pain, trigeminal neuralgia (tic doloreaux) and pain associated with multiple sclerosis. Spinal nerve injury, or radiculopathy, is a type of neuropathic pain associated with neck or low back problems. This is the pain that "shoots" down the arm or leg, because the nerve root is compressed or irritated at the spinal column.

Since neuropathic pain is different than injury related pain, it also needs to be treated differently. For instance, opioids like morphine may not be as effective for neuropathic pain for some people, but other types of drugs such as membrane stabilizers (gabapentin, carbemazepine) or tricyclics (amitriptyline) can be very effective for neuropathic syndromes. One specialized type of treatment for neuropathic pain is a spinal cord stimulator. This device helps control pain by delivering precise electrical pulses to the spinal cord and blocking pain signals before they reach the brain.

4. What is sympathetically-mediated pain (complex regional pain syndrome)?

Complex regional pain syndrome (CRPS) is another type of neuropathic pain. It is also know as reflex sympathetic dystrophy (RSD), causalgia, sympathetically maintained pain, as well as several other names. This serious pain disorder may result from a major injury, but it also can be caused by a relatively minor trauma. Why CRPS occurs still remains unknown, but no matter what the cause CRPS is associated with severe, debilitating pain. The pain can be so intense that even lightest touch can be excruciating. In addition, the affected limb will usually show signs of abnormal circulation, temperature, and sweating (all associated with abnormal function of the sympathetic nervous system, hence the name reflex sympathetic dystrophy), loss of function, and eventually atrophy of muscles and changes in the hair and skin.

Diagnosing CRPS may often be difficult, because a patient's symptoms and physical findings can mimic other disorders. Unfortunately, there is no specific test for CRPS. The diagnosis is likely if the patient meets certain criteria based on the kind of pain they are having and the symptoms associated with their pain. A block of the sympathetic nerves using local anesthetic has been used to help with the diagnosis, but CRPS can be present even if there is no pain relief after a sympathetic block.

CRPS can sometimes be cured in the early stages with physical therapy, sympathetic nervous system blocks and medication. The longer it remains untreated, however, the less likely the chances of reversing the symptoms. Recognition and treatment should take place as early as possible in the course of the syndrome, but the most important treatment at any stage of CRPS is physical therapy to assist with pain control and to preserve function.

5. How is cancer pain different from chronic pain?

Cancer pain is different from other types of pain for several reasons, and there are special considerations that pain management specialists need to be aware of with cancer patients. Pain associated with cancer can actually arise from many different causes. A tumor can be painful and as it spreads, it can injure other tissues, causing increased pain. Bone pain in particular can be especially severe. Cancer can also affect nerves, resulting in the shooting, burning, or aching characteristics of neuropathic pain. There can be pain associated with some cancer treatments such as chemotherapy, radiation, or surgery. Complications from cancer such as infection, bone fractures or even bruises from multiple intravenous lines can cause additional pain. In addition, weakness and fatigue (which may occur with chemotherapy) may make any type of pain worse, and this can be especially true for cancer patients.

Unlike many chronic pain syndromes, cancer pain will often progress, sometimes rapidly, so treatment has to be adjusted frequently, and opioids (like morphine) may need to be prescribed at higher and higher doses. Unfortunately, patients may develop tolerance to these pain medications, making them less effective at the same time that their pain is increasing. When this happens, interventional techniques such as spinal pain pumps or destroying pain nerves may offer significant relief for some cancer patients while allowing the dosage of pain medicines to be lowered. This in turn can help avoid the side effects of opioid medicines, such as sedation or confusion. Ultimately, the pain specialist and primary care physician should work as a team to not only control pain but also help patients maintain dignity, quality of life and the ability to be with family and friends.