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.