Herpes Zoster and Postherpetic Neuralgia

Abstract

Herpes zoster is caused by reactivation of the latent varicella zoster virus (VZV ) that causes chicken pox. VZV remains dormant in the dorsal root ganglion or cranial nerve ganglia after chicken pox resolves and can reactivate and cause herpes zoster. It appears predominantly in older adults, but may also occur in immunocompromised patients. The diagnosis of herpes zoster is made based on characteristic skin lesions and pain and itching in the involved dermatome and should be differentiated from contact dermatitis and herpes simplex virus infection. In the acute phase, an antiviral helps to reduce pain and complications and shorten the course of the disease. Antiviral medications should be started within 72 h of the onset of lesions. Postherpetic neuralgia (PHN) is defined as pain in the affected dermatome that is still present 1 month after the onset of vesicles. Between 10% and 40% of patients with herpes zoster develop PHN, and the incidence increases with age. Adults older than 60 should receive a herpes zoster vaccine. A single shot of the vaccine can cut the risk of getting shingles by about 50%. The diagnosis of PHN is based on a history of herpes zoster, typical dermatomal distribution of the pain, and hyperalgesia and/or allodynia on physical examination. A large number of medications have been used to treat PHN, although only lidocaine patch, pregabalin, gabapentin, and 8% capsaicin patch are approved by the Food and Drug Administration (FDA) for this indication. In refractory cases, several interventional options may be indicated.