Anne Louise Oaklander, MD, PhD, on Neuropathic Pain, Shingles, and Pain Prevention

Pain is a major public health problem. According to the 2011 report by the Institute of Medicine, at least 116 million adult Americans experience some form of chronic pain each year, a condition that costs the nation approximately $600 billion annually. Age is a major risk factor for pain with many painful conditions -- such as arthritis and shingles -- far more common in older adults. Dr. Anne Louise Oaklander, a 1999 recipient of the Paul B. Beeson Career Development Award in Aging Research, answers some questions about common yet lesser known causes of pain.

What is neuropathic pain? What causes it?

Neuropathic pain is a major subset of chronic pain that many people don’t know exists. While pain normally is associated with injury or illness, neuropathic pain often arises in seemingly healthy parts of the body without obvious illness or injury in the painful area. Doctors and patients sometimes refer to it as “mystery pain.” Patients with neuropathic pain often have a hard time getting a correct diagnosis and effective treatment.

There are many types of neuropathic pain; among the most common are the small-fiber polyneuropathies, which can cause widespread pain; the trigeminal neuropathies on the face, and post-herpetic neuralgia (PHN), a condition triggered by shingles.

Small-fiber polyneuropathy involves degeneration of nerve endings usually perceived to cause pain in the feet. Over time this can spread up to affect the hands as well and sometimes the whole body. Diabetes, certain cancers and chemotherapy drugs, nutritional deficiencies, and even autoimmune disorders can cause this.

Trigeminal neuropathy refers to neuropathic pain on the face. The best known form, trigeminal neuralgia or tic douloureux, often responds to surgical treatment. In some people, talking, chewing, or even a simple breeze can cause great pain.

Post-herpetic neuralgia is a regional chronic pain that lingers after an episode of shingles. While most patients recover within six months, older patients can have PHN for years or indefinitely.

To help determine the causes of neuropathic pain, it is important to see a neurologist and sometimes a peripheral nerve specialist.

What is shingles?

Shingles is caused by a reactivation of the varicella-zoster virus (VZV), the same virus that causes chickenpox. After a case of chickenpox, the virus can become dormant in the nervous system for life. Decades later as immunity naturally weakens from age and disease, VZV can reactivate to cause shingles as the virus spreads down infected nerves towards the skin where it causes a rash.

The shingles rash consists of painful and sometimes itchy blisters that can range from mild to severe. The worst cases can look like severe burns. The rash usually develops on one side of the body and is most common on the trunk and on the face near the eyes and forehead.

Shingles is more common than people realize -- about one million cases are diagnosed each year.

Shingles is not just “adult chickenpox.” The rash is often far more severe and painful, and it is more dangerous. Rare complications include blindness, strokes, encephalitis, and spinal cord damage. Although visible on the skin, shingles is a serious neurological disease.

Age is the biggest risk factor for shingles and post-herpetic neuralgia. While young people can also get shingles, it is far less common and they tend to heal faster and are less likely to be left with PHN.

How does shingles actually cause pain?

Shingles and post-herpetic neuralgia are among the best studied neuropathic pain syndromes. Research from my lab and others has shown that the severity of shingles-induced nerve damage is the main biological predictor of who will be left with chronic pain.

Can shingles be prevented?

Yes. You can dramatically lower your risk of shingles and post-herpetic neuralgia by getting vaccinated. The FDA has approved a shingles vaccine for people over the age of 60 and the Centers for Disease Control and Prevention recommends vaccination, even for people who have already had shingles. The vaccine has been proven to lower your risk of shingles by 50% and PHN by 67%. That’s a lot better than leaving it to chance.

If you think you may have shingles, call your doctor and get a prescription for antiviral medications as soon as possible. Taking antiviral medication within 72 hours of a shingles outbreak can dampen the rash and pain now, as well as reduce the risk of long-term PHN by about 40%.

Visit the CDC website for more information about the shingles vaccine.

What do you recommend people do for chronic pain resulting from shingles?

For those people unlucky enough to develop PHN, there are a number of drugs shown effective including a tricyclic medication called nortriptyline. Tricyclics are a class of medications that were originally used to treat depression but are now more often used to treat neuropathic pain.

Why do some people experience pain more than others for the same injuries?

This is the key question that researchers are trying to answer. There are so many factors individually and collectively that determine our susceptibility to pain. They include heredity, environment, and sometimes even the color of our hair. Studies in lab animals show that what we eat also appears to influence the likelihood of developing neuropathic pain after an injury.

Pain is complicated. There aren’t always concrete cause and effect answers, and opinions vary among specialists. That is why it is important to continue research into the causes and treatments for neuropathic pain.

04/16/12