Annular lichenoid dermatitis of youth mimicking mycosis fungoides: a case report

Abstract Introduction Annular lichenoid dermatitis of youth (ALDY), presents as annular, red macules/patches with central hypopigmentation, mainly in the groin, flanks, and sometimes axillae. It can mimic inflammatory morphea, mycosis fungoides, vitiligo, or annular erythema. Histologically, ALDY exhibits interface dermatitis, affecting rete ridge tips, with keratinocyte apoptosis resulting in a squared-off rete ridge base morphology, which distinguishes it from other lichenoid dermatoses and mycosis fungoides. Case report A 21-year-old Iranian female had a stable, asymptomatic annular plaque on her right flank for 1 year. The lesions appeared initially as red macules that coalesced into patches. Examination showed raised borders and central hypopigmentation. The initial biopsy raised suspicion of mycosis fungoides; however, ALDY was also considered. Subsequent clinicopathological and immunohistochemical findings favored ALDY. Clobetasol treatment resulted in significant regression. Conclusion We should consider ALDY in the differential diagnosis of similar lesions within the age range or with trigger factors, but rule out MF first to avoid overdiagnosis.