Postherpetic Neuralgia

Herpes Zoster is caused by the reactivation of the same virus which causes chickenpox. If you have had chickenpox before, the virus lies inactive in the nervous system till the time it gets an opportunity (such as in old age or when the body’s immunity is reduced) to spread along the nerve. This produces the typical rash of Herpes Zoster accompanied by pain, numbness, itching, skin pigmentation and sometimes scarring. One out of five patients goes on to develop PHN where the pain persists for more than 120 days after the onset of rash. PHN is rare in the age group below 50 years and incidence increases after the age of 60 years.

Risk factors for PHN or persisting pain include older age and widespread rash with severe pain at the onset.PresentationPain character in PHN is generally burning, shooting, throbbing or electric shock-like and this may occur spontaneously or in response to stimuli. It is most commonly observed in the chest wall region (thoracic dermatomes) and in the distribution of the ophthalmic branch of the trigeminal nerve (around the eye). You may find the pain is more severe at night time and during periods of stress. It is often accompanied by hypersensitivity of the involved area. In some cases, muscle weakness may be present. About half of the patients recover within a year and in the remaining the course is variable. In one study it was observed that the proportion of patients with spontaneous resolution of pain decreased with increasing time since the onset of herpes zoster. Management Prevention of PHN is important and includes vaccination, early use of antiviral agents.

Acute pain control at the time of onset is important. In selective cases, oral steroids are considered. Those with persisting pain can be challenging to treat and Multi-disciplinary approach is preferred. Drug combination therapy is often used with a combination of systemic medications and topical agents (gels/patches /creams). Unfortunately, some of the topical options such as 8% capsaicin patch, 5% lidocaine patch are not available in India currently.Apart from medications Interventions/ injections such as nerve blocks, drug infusions, neuromodulation is a reasonable option to consider. Sympathetic nerve blocks including stellate ganglion block are often used. Most evidence suggesting short-term benefits and hence they may need to be repeated. It is important to address any concomitant psychological factors and maladaptive coping mechanisms.

