If you thought chickenpox was a "once and done" childhood illness, you're only two-thirds right. For about one million American adults each year, that long-forgotten rash returns in a new painful form: shingles.
The pain of shingles can be excruciating, but the condition goes away in a few weeks -- for most people. In some unlucky folks, shingles pain doesn't end when the rash goes away. It goes on. And on. This is called postherpetic neuralgia (PHN), a form of neuropathic pain that can last for months or years, even after the virus is no longer active.
"Postherpetic neuralgia can make people feel truly miserable," says Jeffrey Rumbaugh, MD, PhD, assistant professor of neurology at Johns Hopkins University and a member of the American Academy of Neurology. "For some, it's something they live with once in a while. For others, it can be daily, severe pain that may last a lifetime."
Some people are at higher risk for shingles and postherpetic neuralgia than others. But when used correctly, available treatments can prevent postherpetic neuralgia or at least stop it from becoming a permanent, painful companion.
What Causes Shingles Pain?
Chickenpox, shingles, and postherpetic neuralgia all result from infection with a single virus called varicella zoster virus (VZV). Most people catch the varicella zoster virus as children, itch and shiver through the rash and fever of chickenpox, and get better.
But that's not necessarily the end of the story of varicella infection. After a bout of chickenpox, our immune systems never completely eradicate the VZV virus. They just chase it into hiding. Varicella retreats into nerve cells deep under the skin, near the spine.
For most of us, VZV lies dormant inside our bodies throughout our lives, never causing further problems. In about one-third of people, however, VZV infection has a second act. The virus emerges from hiding, travels along a nerve to the skin, and erupts in a bumpy, painful rash on one side of the body. This sneak attack is called herpes zoster, or shingles. (Varicella zoster virus belongs to the family of herpes viruses, but does not cause cold sores or genital herpes.)
Shingles Symptoms: What Should You Look For?
Unlike the whole-body rash of chickenpox, the shingles rash is limited to the area of skin assigned to the infected nerve. The rash usually consists of small bumps that may turn into blisters before bursting and crusting over. If shingles appears on the face, the eye can be affected, posing a threat to sight.
Also unlike chickenpox, this rash hurts, sometimes intensely. People typically describe shingles pain as burning, stabbing, or electrical.
"Shingles can be almost unbearably painful," says Jeffrey Ralph, MD, assistant professor of neurology at the University of California in San Francisco and a fellow of the Neuropathy Association. "The nerve itself is inflamed. The pain can sometimes come even weeks before a rash appears."
When Shingles Becomes Painful Postherpetic Neuralgia
In 10% to 20% of these people, however, the pain of shingles keeps hanging on after the rash is gone. "These folks go on to get postherpetic neuralgia, and we're not exactly sure why," Ralph tells WebMD. "Either the pain of shingles never leaves, or it resolves, comes back, and never goes away completely."
PHN typically occurs in the area where the shingles occurred. The pain can be intermittent or constant, and it can take on any of the diverse qualities of shingles pain. Normal touching of the skin can set it off, Ralph adds. This is called allodynia.
The pain of postherpetic neuralgia can interfere with daily activities, exercise, sleep, and sexual desire. Irritability and depression often follow. "Generally, it makes people feel terrible if it can't be controlled," Rumbaugh says.
Why the pain of postherpetic neuralgia persists has mystified researchers. It's not due to ongoing infection by VZV, but is thought to be due to residual damage or inflammation in the nerve after shingles resolves. It's also impossible to predict who'll get shingles or postherpetic neuralgia, although age, race, and health seem to have some impact.
Shingles and Postherpetic Neuralgia: What Are the Risk Factors?
You can't control whether you'll catch the chickenpox virus. Fully 99.5% of adults in the U.S. carry it, whether or not they remember having had chickenpox. But why do one-third of those people get shingles -- and some of them go on to develop postherpetic neuralgia?
The risk of postherpetic neuralgia also goes up with age. More than 80% of cases of postherpetic neuralgia occur in people over 50 years old. "It's likely that the natural decline of immunity with age is responsible," says Ralph.
The results of one study showed that age had a huge effect on the risk for postherpetic neuralgia after shingles:
- Among people under 60 years old who had shingles, less than one in 50 developed postherpetic neuralgia.
- In people aged 60 to 69, about 7% of shingles sufferers developed postherpetic neuralgia.
- In those age 70 and older, almost 20% developed postherpetic neuralgia after a bout of shingles.
Race seems to matter, too. For unknown reasons, white Americans get shingles and postherpetic neuralgia at more than twice the rate of African-Americans in their age group.
"People whose immune systems are impaired by drugs or diseases like AIDS are also more prone to zoster and PHN," adds Ralph.
Exposure to someone with chickenpox or shingles does not increase your personal risk, however. In fact, experts believe that the slight immune stimulation may boost natural defenses, making you less likely to develop shingles or PHN.
Vaccine Prevention for Shingles and Postherpetic Neuralgia
In 2006, a vaccine to prevent shingles came onto the market. Called Zostavax, the vaccine cuts the likelihood of getting shingles after chickenpox by about half, dramatically reducing the number of people who might get nerve pain after shingles.
Based on these results, the CDC recommends Zostavax to all adults age 60 and older. Rumbaugh goes further: He suggests you get vaccinated at any age if you have had shingles. His clinical experience suggests the vaccine helps reduce postherpetic neuralgia even after infection with the varicella zoster virus.
Early Intervention Is the Key to Treatment
Antiviral medicines such as valacyclovir (Valtrex), famciclovir (Famvir) or acyclovir (Zovirax), taken orally, are usually used to treat shingles. When taken at the very beginning, Ralph says, they can improve symptoms and reduce the risk of postherpetic neuralgia.
Starting antiviral treatment for shingles more than three days after symptoms start is generally believed to be ineffective because the virus is no longer reproducing. Still, many doctors will try treating the condition with antiviral drugs after this time.
An aggressive, early approach to controlling shingles pain may also reduce a person's chance of developing PHN. In one study, people who started taking amitriptyline (Elavil) for shingles pain as soon as a rash appeared had less pain after six months than those taking a placebo.
"Rapid initiation of treatment for shingles is very important," says Rumbaugh. "If treatment is started in the first three days, it can reduce the chance of postherpetic neuralgia and make it less severe if it does occur." This window of opportunity is often missed, however, because most people don't get to the doctor that quickly.
Postherpetic Neuralgia Treatment: Soothing the Pain
Once postherpetic neuralgia occurs, antiviral drugs can't treat the pain because ongoing infection isn't the problem. Instead, treatment aims to soothe and quiet the misfiring nerves that are creating the pain.
There are a variety of oils and creams available at drugstores. Some turn to herbal oils and creams, such as extracts from geranium, lavender, eucalyptus, tea tree, and bergamot.
Others use capsaicin cream, made from hot chili peppers. A drug called Qutenza contains "pure, concentrated, synthetic capasaicin," according to the FDA. Qutenza can be used every three months and is applied by a doctor via a patch or patches placed for an hour on the places on the skin that hurt. Before applying the patch, the doctor spreads a topical anesthetic on the area to be treated.
Ralph said many people find relief from the anesthetic lidocaine, available in low-concentration creams or patches over the counter, or by prescription in higher concentration patches.
"The lidocaine soaks through the skin and numbs the painful nerve endings," says Ralph. Lidocaine patches are particularly helpful for people with allodynia, Ralph adds.
If topical creams and oils don't provide sufficient relief, Ralph recommends asking your doctor about prescription medicines that may help, including some antidepressants, anti-convulsants, and opioids.
Postherpetic Neuralgia: Finding the Right Treatment for You
Experts agree that for everyone at risk, prevention is the best treatment. Although it's too early to see a benefit from vaccination in the community, Ralph believes that it shows promise.
For those who have postherpetic neuralgia, treatment needs vary widely. "Some people may only need a few months of a topical anesthetic," Rumbaugh tells WebMD. "Others -- not many, thank goodness -- take multiple medicines for the rest of their lives and still have pain."
Finding the right treatment for persistent postherpetic neuralgia can be a long and frustrating process. "It can take several weeks to really give a medicine a chance to work," Rumbaugh says. "If it's not working, you have to start all over again."
The important thing is not to give up. People with severe postherpetic neuralgia should see a neurologist or pain expert, says Rumbaugh. "There are people who think their pain isn't treatable, who simply haven't been tried on the right doses of the right medicines. There's usually something more we can try."