Nerve pain: What you don’t know may hurt you

For most people, pain is useful. It alerts them to danger, gets them out of harm’s way, and encourages them to cuddle injuries until they heal. But thousands endure a different sort of pain – pain that serves no purpose and persists even in the absence of external hazards. This is neuropathic pain, caused by the damage or deterioration of nerves. A related term is neuralgia, which refers to pain that extends along one or more nerves.

Neuropathic pain can range from an occasional tingling in the hands or feet to a persistent burning or stabbing sensation. Some people experience such heightened sensitivity that even the brush of bed sheets or a soft breeze can cause excruciating pain. Unable to sleep or maintain a routine, people with this kind of pain may grow depressed from their relentless suffering. Because its causes are complex – and successful treatment challenging – the condition can frustrate doctors and patients alike. Gradually, however, researchers and doctors are getting a handle on what causes neuropathic pain. Treatment has improved. Today, most people can get some measure of relief.

Many Causes

Disease, poor nutrition, injuries, or faulty blood flow can damage nerves. If the motor nerves that control muscles are affected, the result can be weakness. If the autonomic nerves – which control rectal bodily functions – are damaged, the circulating and digestive systems can go awry. Sexual function may be hampered. Damage to the sensory nerves can lead to numbness or – paradoxically – pain. The long peripheral nerves of the arms and legs are especially vulnerable. About 20 percent of people over age 60 have some peripheral nerve damage.

Many people with diabetes eventually suffer from nerve damage. Estimates of how many are affected range greatly, from 10 to 90 percent, depending on how neuropathy is defined. Stocking and glove neuropathy is especially common in diabetes. It may lead to a chronic burning pain that begins in the feet and hands and spreads to the upper limbs and trunk. Because alcohol can damage nerves, alcoholics are also prone to this kind of neuropathy.

Other conditions that can damage peripheral nerves include hypothyroidism, an inactive thyroid gland, and several of the autoimmune diseases, such as rheumatoid arthritis or lupus. Nerve damage can also result from exposure to certain chemicals, including heavy metals like arsenic, lead, and thallium; pesticides; and some of the medicines used to treat AIDS, TB and cancer.

Shingles

Sometimes, only a single nerve is damaged, although that doesn’t mean there is any less pain. For example, carpal tunnel syndrome results from prolonged pressure on the nerve that travels through the wrist. A fracture or tumor can harm a nerve by pressing on it. The varicella-zoster virus that causes chickenpox and herpes zoster, which is often referred to as shingles, can also be a source of nerve pain. Shingles is the reactivation of a "silent" varicella-zoster infection following a case of childhood chickenpox. About half of the shingles sufferers age 60 and over will experience lingering pain, most often in the chest and face. The severity and duration of postherpetic neuralgia, as doctors call it, increases with age.

Vitamin B Deficiency

Poor nutrition, especially deficiencies in the B vitamins, can lead to neuropathy. People with pernicious anemia, which occurs when vitamin B12 cannot be absorbed, usually experience relatively mild tingling or "pins and needles" sensations. Alcoholism and eating disorders like anorexia may set the stage for nutritional deficiencies with a variety of negative health consequences, including neuropathy. If the damage is widespread, it is called polyneuropathy.

But in many cases, the cause of neuropathic pain remains elusive. Of the people who go to the doctor complaining of pain in their hands and feet, about one-third turn out to have diabetes. Doctors can find a cause, such as alcoholism, for another third. But for the rest, even an exhaustive medical and neurological work-up reveals no clear reason for the condition.

Relief

The first step in relieving neuropathic pain is to address any underlying problem. If vitamin B deficiencies are to blame, taking supplements will usually help, although sometimes, injections are necessary. Too much of some B vitamins can be dangerous, so a doctor should oversee such treatments. For people with diabetes, the key is keeping a tight rein on blood sugar levels. It may also help to exercise, limit alcohol, and quit smoking.

Patients who have painful feet with no known cause should think about what they might be doing to harm peripheral nerves. The most common culprit is alcohol. Even people who are not alcoholics may suffer from nerve pain caused or exacerbated by drinking. Poor foot care can lead to neuropathy and pain. Injuries to feet with damaged nerves, such as people with diabetes and leprosy, can develop into ulcers, which in the worst case can lead to amputation.

Medications

Aspirin, acetaminophen (Tylenol), or other common pain relievers rarely relieve neuropathic pain. Topical analgesics, pain relief medicines applied to the skin, may help with peripheral neuropathies. For example, creams containing capsaicin, the active ingredient in chili peppers, often help with pain from postherpetic neuralgia. The cream may burn when first applied, however, and it may take several weeks of continual use for it to have full effect. Capsaicin creams can also relieve stocking and glove neuropathy, although it can be hopelessly messy if you have to spread it over a wide area. Studies have found that lidocaine skin patches also reduce postherpetic pain. Topical prostaglandin is promising although the data are only preliminary.

Tricyclic antidepressants, such as amitriptyline, often help alleviate the burning and stabbing pain of shingles and diabetic neuropathies. They usually work sooner and at lower doses for pain than for depression. But the tricyclics have many side effects, including drowsiness, dizziness and – especially for people in their 70s and 80s – constipation. Newer antidepressants, like fluoxetine (Prozac), have fewer side effects and may relieve some neuropathic pain, but their track record is not as well established.

Anticonvulsant medications can also be a useful treatment, especially for individuals who can’t tolerate antidepressants. In the 1950s, carbamazepine (Tegretol) was introduced as a highly effective treatment for trigeminal neuralgia, pain coming from one of the main nerves in the face. It is among the most excruciating of chronic pain conditions. The drug turned out to be an excellent anticonvulsant as well, and is now a mainstay in the treatment of epilepsy. Carbamazepine and other anticonvulsants that calm overexcited nerves continue to help some people with chronic nerve pain.

A relatively newer anticonvulsant, gabapentin (Neurontin), has fewer side effects and interacts less often with other drugs than carbamazepine. Research has found it effective against postherpetic and diabetic nerve pain. Mexiteline, used to treat heart arrhythmias, may also help some pain patients for whom antidepressants and anticonvulsants have failed. Like several other promising new drugs, it can cause side effects, and it’s not clear how often doctors will wind up prescribing it. Narcotics are highly effective against pain. But partly because they carry the risk of addiction, doctors are reluctant to prescribe them save as a last resort for people with terrible pain that can’t be relieved by other means, such as some cancer patients.

Other Kinds Of Help

Unfortunately, people with nerve damage often go through a great deal of trial and error before finding something that works. Physical therapy may be tried. Acupuncture has helped some people. Biofeedback and meditation can relax the muscles and give comfort. Some people benefit from transcutaneous electrical nerve stimulation (TENS), in which electrodes on the surface of the skin stimulate the nerves.

Chronic neuropathic pain is physically and emotionally draining. Support groups or psychotherapy may help sufferers. The nonprofit Neuropathy Association (www.neuropathy.org) is a good resource.

Many investigators are experimenting with nerve growth factor, a class of proteins that affect nerve growth and regeneration. So far, the trial results have been mixed.

The Bottom Line

For now, the best approach really is prevention. For example, you can reduce your risk for painful neuropathies by eating a balanced diet rich in B vitamins, watching your alcohol consumption, steering clear of dangerous chemicals, exercising, and controlling your blood sugar if you have diabetes.

Pain conditions are underdiagnosed and undertreated, especially in the elderly. If you’re in constant pain, don’t be stoic. Visit your doctor. Like most pain, neuropathic pain is best treated promptly and aggressively. The longer it persists, the harder it is to conquer. The earlier it is treated, the greater is your chance of successfully relieving nerve pain.