Risk factors for postherpetic neuralgia in patients with herpes zoster

Objectives: To identify risk factors for postherpetic neuralgia (PHN) using a validated definition of this chronic neuropathic pain syndrome, to determine combinations of risk factors that identify patients with a high risk of developing PHN, and to examine the characteristics of patients with subacute herpetic neuralgia, that is, pain that persists beyond the acute phase of herpes zoster but that resolves before PHN can be diagnosed. Methods: The authors examined baseline and follow-up data from 965 herpes zoster patients enrolled within 72 hours of rash onset in two clinical trials of famciclovir. Results: Univariate and multivariate analyses indicated that older age, female sex, presence of a prodrome, greater rash severity, and greater acute pain severity made independent contributions to identifying which patients developed PHN. Patients with subacute herpetic neuralgia who did not develop PHN were significantly younger and had less severe acute pain than PHN patients but were significantly more likely to have severe and widespread rash than patients without persisting pain. Conclusions: The independent contributions to the prediction of PHN made by older age, female sex, presence of a prodrome, greater rash severity, and greater acute pain severity suggest that these risk factors reflect different mechanisms that each contribute to the development of PHN. Subacute herpetic neuralgia that does not progress to PHN may reflect peripheral tissue damage and inflammation caused by a particularly severe or widespread rash.