Herpes zoster is a viral infection due to reactivation of Varicella zoster virus or chicken pox virus which lies dormant in the dorsal sensory ganglia and cranial nerve ganglia for many years. Reactivation of this virus is seen in the form of
vesicular dermatomal rash. Pain due to herpes zoster rash is the acute pain, due to inflammation and neuronal destruction. The pain affects quality of life and interferes with activities of daily living. Vaccination against Herpes zoster can prevent this infection.
Initially a person develops prodromal symptoms of itching and abnormal sensation in a defined dermatomal area of the body. There may be headache, fever, nausea, malaise, neck pain or stiffness, flu like symptoms, which last for 3 to 7 days before the appearance of a rash. The rash changes from maculopapular to vesicular with erythematous base and then pustular. Later it forms scabs and clears up in 2 to 3 weeks , the whole event occurs over a month’s time and leaves
a hypo or hyper-pigmented scar.
Acute pain, itching, paraesthesia, dysaesthesia may begin before the rash is seen or occur as the rash develops. Pain may be constant or intermittent. It is associated with tactile sensitivity and allodynia, i.e. even a normal stimulus appears painful. The quality of pain is burning, throbbing, stabbing or like electric shock or may be a combination of these. There are sleep disturbances Acute pain resolves as the rash disappears, this pain occurs within 30 days of the
onset of rash Sub-acute herpetic neuralgia persists beyond 30 days from the onset of rash. If pain persists for 120 days or beyond, after the onset of rash, it is Post HerpeticNeuralgia.
Thoracic dermatomes are commonly affected. Ophthalmic division of trigeminal nerve, other cranial nerves, and cervical, lumbar and sacral dermatomes are affected in this order of incidence.