Postherpetic neuralgia (PHN) is the most common complication of herpes zoster. Patients older than 60 years of age have a higher risk of PHN than do the younger patients. 1,2 There are many definitions of PHN in the literature in terms of timing (following rash healing, versus a defined time after onset of herpes zoster, 1 or 2 mo), duration (any time after zoster or a minimum of 6 mo after zoster), and type of pain (such as lancinating pain or allodynia). 3 PHN may include a wide array of presentations, from brief intermittent mild pain that resolves spontaneously to chronic recalcitrant, persistent, and severe pain unremitting to multiple therapies. A prospective study conducted on 457 patients with herpes zoster suggests that a physician can expect to see 4 cases of herpes zoster per year and 1 case of PHN lasting more than 3 months every 3 years. 4 Meta-analysis of 42 randomized controlled trials of acute zoster treatments have shown the incidence of pain at 3 months to be between 17 and 60%. 5 There is limited evidence that any of the conventional therapies for treating acute zoster have an impact on development of PHN. 5,6
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