Herpes Zoster produces two painful conditions: Acute Herpes Zoster (Shingles) & Post- herpetic neuralgia.
Acute Herpes Zoster (Shingles):
It occurs in adults have been infected with chicken pox virus in early life. It has been postulated that chicken pox virus remain in dormant state at the dorsal root ganglion. When it get favorable condition (like immunosuppressive drug therapy, malignancy like lymphoma) it flares up. They multiply at dorsal root ganglion and migrate down the sensory nerve to the nerve endings. They erupt on the skin and produces vesicular lesion. The lesion may erupt in the region of thoracic, cervical, lumber area and along the distribution of ophthalmic division of Trigeminal nerve.
Acyclovir, analgesics, antidepressants and corticosteroids are indicated in acute stage. Local infiltration of steroids and nerve block (including epidural block) are effective when pain is severe.
Post- herpetic neuralgia (PNH):
It is defined as pain, paresthesia & allodynia (pain on touch) persisting for more than 4 week after an attack of Acute Herpes Zoster. Pain of PHN may be deep burning pain, sharp stabbing pain, and throbbing or lancinating pain. It is associated with allodynia.
Drugs used in PNH are gabapentine, Carbamazepine, Clonidine, Amitriptyline, and Lignocaine etc. Interventional Pain Management procedures like intercostal nerve block, stellate ganglion block, thoracic or lumber sympathetic block and paravertebral block give excellent and permanent/long lasting pain relief.