Isoradiotopic response of discoid lupus after radiotherapy: A case report and review of the literature.

Radiotherapy is frequently associated with a great number of collateral effects, which can affect the skin and its appendages. In addition to more common side effects, like radiodermatitis, other cutaneous conditions are less known and often they are underdiagnosed. Among these, isoradiotopic response is one of the rare radiotherapy-associated phenomena. This term refers to the appearance of a secondary dermatosis in a previously irradiated district. The term was used for the first time by Shurman et al. to describe a case of lichen ruber planus arising in the genital area after radiotherapy for squamous cell carcinoma. The pathologic mechanism is not completely clear, but a few hypotheses have been proposed. Alterations in the local lymphatic drainage, in the nervous system and the immune microenvironment have all been called into play (the immunocompromised district theory). We present the case of a male patient that developed discoid lupus on a previously irradiated cutaneous area and review the literature, highlighting the numerous possible manifestations of this phenomenon.