Post-herpetic neuralgia in older patients. Incidence and optimal treatment.

Post-herpetic neuralgia (PHN) is a disease caused by having had herpes zoster; it is not a continuation of shingles. Up to 50% of elderly patients who have had shingles may develop PHN. PHN is defined as pain recurring or continuing at the site of shingles, 1 or more months after the onset of the rash. Because many cases resolve spontaneously in the early stages, no claims of 'pharmacological cure' can be entertained before 3 months post-rash. In fact, some authorities will not accept claims made before 6 months. Antivirals administered systemically within the appropriate time-window greatly relieve the pain of acute shingles, and to a large extent prevent scarring. There is no evidence that they prevent the subsequent development of PHN. However, patients with PHN whose acute shingles were treated with aciclovir obtain pain relief with antidepressants in half the time required by those patients who did not receive aciclovir for their acute shingles. If patients with acute shingles are given low dose amitriptyline from the onset, only half as many are in pain at 6 months as a group not so treated, irrespective of the antiviral treatments given. The most effective treatment of established PHN to date consists of adrenergically active antidepressants. There is a strict correlation with the brevity of the interval between acute shingles and initiation of such treatment. 75% of patients starting treatment with antidepressants within 3 to 6 months after shingles obtain pain relief, whereas if antidepressants are not started for 2 years, only 25% obtain pain relief.(ABSTRACT TRUNCATED AT 250 WORDS)