Post-Herpetic Neuralgia

The varicella zoster that causes chicken pox in children can remain latent in sensory ganglia for manyyears after the original infection. Reactivation of this virus manifests as herpes zoster (also known as shingles), a painful rash along a single dermatome related to the affected dorsal (nerve) root or cranial nerve ganglion. Although the condition is usually short lived, persisting for a maximum of 4 weeks, some patients (most often those over 50 years of age) will develop post-herpetic neuralgia, in which pain along the affected nerve territory persists after the acute rash has resolved. Patients may experience a background burning or aching pain accompanied by paroxysmal stabbing or itching. It is thought both peripheral and central mechanisms play a role in the condition.

People suffering from post-herpetic neuralgia (PHN) will confirm that this painful condition is miserable, unremitting, excruciating and worst kind of experience they had any time in their lifetime101. If it were easy to treat it would not be the focus of so much medical attention. If it were impossible to treat then perhaps attention would not be warranted either. Surprising fact is that not every patient who develops herpes zoster will not end with PHN.

Herpes zoster is an attack of erythema and pustular vesicles . This infection is caused by varicella zoster DNA virus. Majority of population would have had an attack of chicken pox by early adulthood. After this attack the virus hibernates in the dorsal root ganglion (nerve centre) and remains dormant for many years. This results in a prolonged carrier state. Reactivation of this virus at a later time results in acute attack of herpes zoster. Why exactly this virus activates at a later time is not clear. Most commonly accepted theory is that as long as cell mediated immunity is strong (which is so in younger population), the virus activity gets suppressed. As the person gets aged the incidence increases. Incidence is 0.4 to 1.6 cases per 1000 in people aged less than 20 years and it is around 4.5 to 11 cases per 1000 among those 80 years or older. People who are in immunocompromised status because of either cancer or HIV status are more prone to get an attack.

The disease most often attacks chest, neck and face areas. The attack often precedes by days or weeks of constant burning pain, aching sensation, hyperaesthesia in one or two adjacent dermatomes. It erupts as red patch (red rash) and soon small groups of vesicles will be seen in that area. Over course of 7 to 10 days the vesicles develop pus and crust formation can be seen. Children can get chickenpox by contact with herpes zoster while adults do not acquire. Once the formed crusts disappear, pigmented or depigmented anaesthetic scar over that area can be easily observed. Even after the initial rash subsides, pain can persist or recur in shingles affected areas. This condition is known as postherpetic neuralgia (PHN). The demarcation between pain due to acute infection and the pain of PHN is not defined. Some define pain persisting beyond the crusting of acute infective lesions as PHN; others, pain after specified periods from 4 weeks to 6 months since the eruption of acute infective skin lesions. There is therefore no clear definition of PHN.

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