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 and cranial ganglia and can reactivate later in a person’s life and cause herpes zoster, which appears predominantly in older adults, but may also occur in those that are immunocompromised. Postherpetic neuralgia (PHN) is defined as pain in the affected dermatome that is still present 1 month after development of the vesicles. Adults older than 50 should receive the herpes zoster vaccine as part of routine medical care. Shingrix is a new vaccine recently approved and recommended by the FDA, which is a non-live, subunit vaccine. In contrast to Zostavax, Shingrix is 97% effective against shingles and 91% effective against PHN for people 50 and older. The diagnosis of herpes zoster can be made on the basis of characteristic skin lesions and pain and itching in the involved dermatome. During the acute phase, an antiviral given within 72 hours of onset helps reduce pain and complications and shorten the course of the disease. 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. First-line pharmacotherapy includes gabapentin or pregabalin, tricyclic antidepressants, and SNRIs. Combination therapies are often necessary. Interventional options such as epidural injections, paravertebral blocks, selective nerve root blocks, sympathetic nerve blocks, intercostal nerve blocks, trigeminal nerve blocks, spinal cord or dorsal root ganglion stimulation, and intrathecal therapy may be considered in refractory cases.