Steroid-modified Tinea Corporis et Cruris Presenting as Chronic Polycyclic Erythematous Plaques Mimicking Psoriasis: A Case Report

Abstract

Tinea corporis et cruris typically presents as annular erythematous plaques with an active scaly border. However, inappropriate use of topical corticosteroids may obscure these classic findings and produce steroid-modified dermatophytosis (tinea incognito). A 61-year-old male presented with a three-month history of pruritic erythematous plaques on the abdomen and right lower limb. The lesions appeared polycyclic, well-demarcated, and mildly scaly, initially raising suspicion for psoriasis. The patient had a history of chronic heart failure and reported applying topical steroid twice daily, which partially suppressed inflammation and altered lesion morphology. KOH 10% examination of skin scrapings demonstrated abundant long, branching, septate hyphae with parallel walls. The final diagnosis was steroid-modified tinea corporis et cruris. After two weeks of therapy, clinical improvement was observed, characterized by reduced pruritus and thinning of the erythematous plaques. Microscopic examination of skin scrapings with a 10% KOH preparation revealed an absence of visible hyphae, confirming a positive therapeutic response.