Postherpetic neuralgia.

Postherpetic pain persisting 1 month or longer occurs in only a small percentage of all patients with herpes zoster. In most patients, PHN tends to diminish with time. The incidence is, however, directly related to age. Any therapeutic claim for prophylaxis or treatment of PHN has to be evaluated with these observations in mind. There is some information about the pathologic features and a concept of the pathogenesis can be suggested. There is evidence for an imbalance in fiber input (reduced large, inhibitory fibers, and intact or increased small, excitatory fibers) to an abnormal dorsal horn that may contain hypersensitive neurons. Prevention of PHN remains difficult. There is evidence that systemic steroids exert a preventive effect when employed in the treatment of herpes zoster in the immunocompetent patient. A reasonable regimen is 60 mg of prednisone tapered over 10 to 14 days. One double-blind, controlled study supports the use of amantadine in this situation; this drug is an option in patients for whom steroids are contraindicated, such as those with peptic ulcer, diabetes mellitus or compromised immune function. The dosage of amantadine used in this study was 100 mg twice daily for a month. Although a number of other therapies have been suggested, these remedies remain in need of further, more scientific study. For established PHN, there is firm support for the reduction of pain from severe to mild in two thirds of patients administered low doses of amitriptyline followed by gradual, small increments. In the age group over 65 years, one may use as small a dose as 10 mg with an increase of 10 mg every 5 to 7 days. In those younger than 65, a dose of 25 mg to start is reasonable, with increments of 25 mg. Although unproved, the addition of a phenothiazine, such as fluphenazine, may provide further pain relief. Preliminary studies also indicate that topical capsaicin may be a useful new treatment. Although widely used, there is no good evidence for the use of anticonvulsants alone in this disorder. Studies of local anesthetic sprays with vibration and continuous TENS are uncontrolled, but these modalities may be of some merit. One uncontrolled study reported benefit from epidural steroids. DREZ lesions are a possibility in failed medical cases, but other surgical procedures appear to be of little or no use. Although the measures described here will benefit a number of patients, PHN remains an intractable problem in some cases.(ABSTRACT TRUNCATED AT 400 WORDS)