A 36-year-old factory worker developed itchy, annular scaly plaques in both groins. Application of a coicosteroid ointment led to temporary relief but the plaques continued to extend at the periphery. The most likely diagnosis is:

Tinea cruris is dermatophytic infection of groin. Presence of bilateral annular scaly plaques in the groin, itching and unresponsiveness to steroids and peripheral extension leads to diagnosis of Tinea cruris. Ref: Anthony Du Vivier, Phillip H. McKee, Chapter 15, "Superficial Fungal Infections", In the book, "Atlas of Clinical Dermatology", Elsivier Publication, 2002, 3rd Edition, Spain, Page 320