Pityriasis rotunda mimicking tinea cruris/corporis and erythrasma in an Indian patient.

Pityriasis rotunda is a rare disease characterized by perfectly round to oval, sharply defined, scaly, hypo/hyperpigmented patches of variable number and size located mainly over the trunk and proximal extremities. More than 95% of the reported cases in medical literature are from three countries/ethnic populations, namely Japan, South Africa (Bantu), and Italy (Sardinian islanders). To the best of my knowledge, no patient with the characteristic clinico-pathologic features has been reported from the Indian subcontinent. I report a 44-year-old man with eighteen pityriasis rotunda patches, persistent for nearly 20 years. The lesions in the groin and axillae closely resembled erythrasma and tinea, and he had received treatment for these conditions several times in the past. Histopathology of the skin biopsy showed thinning of the epidermis with a thinned-out granular layer and a sparse lymphomononuclear infiltrate in the dermis. A review of literature suggests that there are two subsets of the disease. The type I subset is comprised of pityriasis rotunda associated with systemic illness and is seen in Black or Oriental patients with no family history of the disease. The lesions tend to subside on treatment of the underlying illness. The type II subset patients are Caucasians as well as Blacks and Orientals with no underlying systemic illness. Familial occurrence is possible; lesions tend to be persistent and unresponsive to therapy.