Isotopic response after herpesvirus infection: an update

The term postherpetic isotopic response describes the occurrence of a new, unrelated disease that appears at the same location as a previously healed herpetic infection. When dealing with the pathogenetic mechanism involved in the isotopic response, several possibilities should be considered: a viral origin, an immunologic origin, a vascular origin, and a neural origin. The aim of this article is to review and discuss the different pathogenetic mechanisms with particular attention to new information related to the possible neural origin of this abnormal response of the skin.