Postherpetic neuralgia (PHN) is a pain syndrome that for some people is a continuing aftereffect of an outbreak of shingles (herpes zoster). Of the one million cases of shingles in the United States each year, it is estimated that between 10% and 18% will develop PHN.
The chain of events begins when the varicella zoster virus, which has lain dormant in the patient’s nervous system since an earlier case of chicken pox, reactivates and attacks sensory nerve fibers as shingles. Triggers that cause the virus to resurface include age, illness, and stress.
In addition to nerve pain, shingles presents as a red skin rash and blisters that appear usually on just one side of the body, generally on the torso, neck or face. The blisters crust over and heal within 2 to 3 weeks and the pain gradually subsides. When the pain doesn’t subside, PHN is suspected.
The criteria for diagnosing PHN are purely based on time, according to David Simpson, MD, Professor of Neurology and Director of the Neuromuscular Disease Division at the Icahn School of Medicine at Mount Sinai in Manhattan and a member of the American Academy of Neurology. “Most individuals with shingles have an initial pain syndrome during the blistering rash. However, that pain dissipates over time – usually over several weeks – as the rash heals,” he explains. “But in individuals in whom the pain does not dissipate and persists beyond several months after the shingles, then one moves into the chronic condition of postherpetic neuralgia.”
PHN is the result of nerve fibers that were damaged during the shingles outbreak. The fibers’ messages to the brain are exaggerated or confused, causing chronic and sometimes long-lasting pain in the same area of the body where the shingles rash appeared. The pain can be disabling and has been likened to a sharp ache, a burn, or an electric shock. Other symptoms include itching, numbness, muscle weakness or paralysis, and sensitivity to touch, light, and temperature changes.
The single greatest risk factor for shingles and the development of PHN is age. “As people age, particularly into their seventies and eighties and beyond, the risk of shingles and postherpetic neuralgia goes up dramatically,” says Simpson. “Individuals with a weakened immune system such as caused by AIDS, cancer, or chemotherapy drugs are also at risk of shingles.” The duration of the pain differs by individual and can last months or even years before subsiding.
There is no cure for PHN, but treatments are available. Analgesics, anticonvulsants, and topical treatments (including 5% lidocaine and 8% capsaicin patches) have been approved for use by the FDA. Off-label treatments that are commonly used for severe and intractable PHN include tricyclic antidepressants, opioids, and interventional treatments like nerve ablation and injection procedures.
Simpson advises that the best strategy for avoiding PHN is to prevent shingles altogether through vaccination. Two shingles vaccines are approved for people aged 50 and older and have been shown to reduce the incidence of shingles and PHN.