Herpes zoster infection can occur from reactivation of the herpes varicella-zoster virus or from primary infection. In two-thirds of adults, reactivation is characterized by severe pain and paresthesias in a dermatomal distribution, followed 1-2 weeks later by the appearance of a vesicular rash. The thoracic, cervical, and trigeminal dermatomes are most commonly involved. Approximately 25% of patients have residual neuropathic pain lasting greater than 4 months following resolution of the rash, a condition known as postherpetic neuralgia (PHN).

The risk of developing PHN increases with age. In patients with persistent pain following rash resolution, pain and temperature sensation are hyper-acute, leading to severe pain even with light touch (allodynia) or episodes of unpredictable shooting or stabbing pain. PHN is a clinical diagnosis. Neuralgiform symptoms can persist from weeks to a lifetime.

Related topics: varicella, disseminated herpes zoster