Approximately 10 percent of cases of herpes zoster infection result in significant postherpetic neuralgia. The incidence of postherpetic neuralgia rises dramatically with age, with over one half of all cases of herpes zoster in patients older than 60 years resulting in this end-stage disorder. Three distinct types of pain are associated with postherpetic neuralgia: steady burning pain, lancinating episodic pain and allodynia (i.e., pain on stimulation of the skin). Postherpetic neuralgia becomes permanent or persists for many years in about one half of those affected, and most cases are refractory to treatment. Watson reviews the management of postherpetic neuralgia.
In summarizing studies of treatment for postherpetic neuralgia, the author emphasizes that total relief of symptoms is rarely achieved and that most patients report significant side effects from the analgesic or antidepressant medications studied. To date, studies have involved relatively small numbers of patients (24 to 41 subjects), and significant individual variation has been noted in response to treatment. Some antidepressants that have the ability to inhibit neurotransmitters for pain pathways have been studied for their analgesic effect in postherpetic neuralgia. Studies of amitriptyline resulted in reports of poor or no response to therapy in 33 to 53 percent of patients, compared with 84 to 100 percent of those receiving placebo. A study in which amitriptyline was combined with maprotiline also resulted in a report of poor or no response in 53 percent of patients, but another study in which amitriptyline was combined with or substituted for nor-triptyline resulted in poor or no response in only 32 percent of patients. Desipramine given as sole therapy resulted in poor or no response in 54 percent of patients. It is recommended that antidepressant therapy for postherpetic neuralgia begin with small dosages and increase incrementally to achieve the optimal balance of benefit and adverse effects.
Narcotic analgesics are frequently used in the management of postherpetic neuralgia. A study of oxycodone resulted in reports of poor or no response in 45 percent of those treated compared with 82 percent of patients who received placebo. Regional anesthesia may help to control acute pain but has not been systematically studied. It is not known if the vaccination of older adults would attenuate or prevent herpes zoster infection and thus reduce the number of cases of postherpetic neuralgia. Since cell-mediated immunity is believed to play a significant role in the pathogenesis of postherpetic neuralgia, vaccination could theoretically confer protection.
The author concludes that the best approach to minimizing the risk of postherpetic neuralgia is early, aggressive treatment of herpes zoster. Patients should be educated to recognize the signs and symptoms of the condition and should be made aware of the importance of early presentation for medical evaluation. Antiviral therapy with valacyclovir or famciclovir should begin within 72 hours of onset of pain or rash.