When Lupus Isn't Lupus: Erythema Marginatum in an Adult with a History of Acute Rheumatic Fever.

Erythema marginatum is a rare but diagnostically valuable cutaneous manifestation of acute rheumatic fever (ARF), particularly in young individuals with a history of streptococcal infection. Its presentation is often transient and underrecognized in adult populations, especially when mimicking other annular dermatoses such as subacute cutaneous lupus erythematosus (SCLE). A young woman in her early twenties with a history of ARF and residual rheumatic valvular involvement presented with recurrent, asymptomatic annular erythematous plaques. Initial diagnostic considerations included dermatophytosis and SCLE. Skin biopsy showed chronic dermal inflammation with a perivascular and periadnexal lymphoplasmacytic infiltrate, without lupus-specific histopathologic features. In the appropriate rheumatic context, these findings supported erythema marginatum as a clinicopathologic diagnosis of exclusion. Our case highlights the importance of considering erythema marginatum in the differential diagnosis of recurrent annular dermatoses in patients with a history of ARF. Clinicopathologic correlation remains essential to ensure appropriate management.