Herpetic Zoster

Herpes Zoster and Postherpetic Neuralgia
Herpes zoster is a viral infection caused by the reactivation of the varicella-zoster virus (VZV). The primary varicella infection occurs when the patient contracts chicken pox. Following the resolution of chicken pox, the virus then remains dormant in dorsal sensory ganglia and cranial nerve ganglia for years to decades. Individuals are asymptomatic while the virus is dormant, and reactivation of VZV results in a characteristic vesicular dermatomal rash. Some patients with herpes zoster develop Post Herpetic Neuralgia (PHN) and this persisting neuropathic pain can last for years

Pain
Pain often precedes or accompanies the herpes zoster rash. Pain may be accompanied by other sensations such as itching, paraesthesias, and dysaethesias. The pain is variously described as burning, throbbing, stabbing, electric shock-like, or various combinations of these. It is frequently associated with increased tactile sensitivity and allodynia (i.e., pain in response to a normally nonpainful stimulus). The acute pain associated with herpes zoster gradually resolves in most patients around the time that the rash resolves. Pain that persists beyond the acute phase of the rash is considered subacute herpetic neuralgia or PHN, depending on its duration.

DERMATOMAL DISTRIBUTION OF HERPES ZOSTER IN IMMUNOCOMPETENT PATIENTS
Thoracic: up to 50% of all cases
Cranial: 10% to 20%
Cervical: 10% to 20%
Lumbar: 10% to 20%
Sacral: 2% to 8%
Generalized: <1%

CLINICAL PICTURE OF PHN
Currently, the term PHN is used to describe dermatomal pain that persists for more than 120 days after the onset of the herpes zoster rash.

Tactile allodynia can be so severe that patients with truncal PHN may not be able to tolerate the sensation of clothing against their skin. PHN may not be able to wear hats, glasses, or tolerate even breezes or air conditioning on the affected site.

TREATMENT OF PHN
Anticonvulsants: Gabapentin and Pregabalin
Tricyclic Antidepressants
Opioid Analgesics
Topical Lidocaine
Topical Capsaicin

Intercostals Nerve Blocks
Intercostal nerve blocks have been reported to provide long lasting relief in PHN patients