Wolf's isotopic response: The first attempt to introduce the concept of vulnerable areas in dermatology.

The term isotopic response was coined in 1995(1) to describe the occurrence of a new skin disorder at the site of another, unrelated, and already healed skin disease. That publication paved the way to recognition of this phenomenon by the medical community worldwide with multiple reports describing it under a variety of conditions. The term isotopic response, however, turned out to be unsuitable for a Medline search, because it generated hundreds of references linked with radioactive isotopes. To facilitate Medline searches for this dermatologic phenomenon by avoiding unnecessarily time-consuming sifting through so many unrelated references, it was suggested that the name Wolf be added. The name Wolf's isotopic response has since been generally accepted and even included in Stedman's Illustrated Dictionary of Dermatology Eponyms. Although the concept of the isotopic response was conceived as being analogous to Köbner's isomorphic response, and despite the similarities between the two terms, the similarities are only "skin deep," and there is a major difference between the two. Isomorphic response means "the same morphology" (as that of the existing disease) and describes the appearance of the same disease at another location. The term isotopic response describes the appearance of an altogether different disease at the site of an already healed skin disease. We describe this entity and present representative clinical examples. Some problems in the definition of Wolf's isotopic response are provided, with special emphasis on its overlapping with Köbner's isomorphic response. The description of Wolf's isotopic response, which is analogous but not identical to the isomorphic response described some 120 years ago by Köbner, illustrates the contribution of morphologic findings and original ideas in keeping up with the ongoing progress in the field of dermatology.