Herpes zoster and postherpetic neuralgia.

Pain associated with herpes zoster arise from the virul neuritis of the suffered trigeminal or spinal dorsal ganglion. Prolonged neuritis makes an irreversible nerve injury and continuous pain impulse develops a central sensitization. A post-herpetic neuralgia is thought to be a neuropathic pain due to the irreversible nerve injury and sensitization. It is important to treat herpetic pain completely before the development of the post-herpetic neuralgia, because there are few effective therapies to cure post-herpetic neuralgia. A sympathetic nerve block increases the nerve blood flow supply, and may improve the nerve injury. It is also known that some sympathetic mechanisms relate to the development of the sensitization. A sensory nerve block reduces pain impulse to the dorsal horn, and may interfere the sensitization. A cortico-steroid administrated with a nerve block can reduce the neuritis, and may improve the nerve injury.