ISOTOPIC RESPONSE

Background. The occurrence of a new skin disorder exactly at the site of another one, already healed and unrelated, was first described in 1 955. In 1985, Wolf et al. recognized that we are dealing with a dermat ologic phenomenon and established a precise definition for this phenom enon. Fifty-eight cases corresponding to the definition of this phenom enon have been reported until now. Methods. The new phenomenon, for wh ich the term ''isotopic response'' has been suggested, has been define d. Cases corresponding to the definition have been analyzed with speci al emphasis on the diseases involved, the time intervals, and the loca tions of the diseases. Eight new cases are described. Results. A total of 58 cases of isotopic response have been described. The first disea se in most of the patients was herpes tester; in three cases it was he rpes simplex, in two varicella, and in one, thrombophlebitis. The seco nd disease, which appeared exactly at the site of the first, already h eated disease, was in most reported cases a carcinoma (26 cases, in pa rticular 15 cases of breast carcinoma, 5 basal cell carcinomas (BCC), 4 squamous cell carcinomas (SCC), 2 basosquamous carcinomas), or granu loma annulare (16 cases). Additional diseases were Kaposi's sarcoma (2 cases), pseudolymphoma (2 cases), sarcoid (2 cases), tinea (2 cases), tuberculoid and vasculitis granuloma (1 case), angiosarcoma, metastas is, Bowen's disease, lymphoma, leukemia cutis, and acne (1 case each). The diseases did not show any predilection for a particular location. The interval between the first and second disease was extremely varia ble (ranging from days to years) and showed no particular features. In the eight additional cases described in the present report, the first disease was herpes simplex (6 cases) or herpes zoster (2 cases). The second disease was viral warts (3 cases) or squamous cell carcinoma (2 cases). Additional diseases were furunculosis, contact dermatitis, an d molluscum contagiosum (1 case each). Conclusions. The new term, ''is otopic response,'' describes the occurrence of a new skin disorder at the site of another, unrelated, and already healed skin disease. It is suggested that the term ''isotopic response'' be included in the lexi con (glossary) of dermatology. Introducing the new term and classifyin g all the cases under a single key word, will make it possible to loca te and collect them easily and to search for the mechanism underlying this phenomenon.