Case Report: Flagellate eruption of adult-onset still disease in an Afro-Caribbean woman: highlighting atypical cutaneous disease in richly pigmented skin

Adult-onset Still disease (AOSD) is an uncommon autoinflammatory disorder characterized by high spiking fevers, arthralgia, and, classically a transient, salmon-colored rash. Atypical cutaneous variants, such as persistent erythematous papules and plaques often arranged in a flagellate pattern, are increasingly reported; however, few cases illustrate this morphology in individuals with richly pigmented skin. We report a 70-year-old Afro-Caribbean woman (Fitzpatrick skin type VI) with persistent high-grade fevers, polyarthritis and diarrhea of unknown origin which persisted despite multiple courses of antibiotics. Laboratory evaluation revealed leukocytosis and transaminitis. Dermatology was consulted for a cutaneous eruption present for three weeks prior to hospitalization. Examination revealed subtle red-brown papules, plaques and patches on the trunk and extremities, some in a flagellate arrangement. Skin biopsy demonstrated hyperkeratosis, individually necrotic keratinocytes in the upper epidermis and a perivascular neutrophilic infiltrate characteristic of the atypical eruption of AOSD. Further blood work confirmed marked hyperferritinemia. Treatment with systemic and topical corticosteroids resulted in improvement. This case underscores the importance of recognizing atypical cutaneous variants of AOSD in persons with richly pigmented skin to prevent diagnostic delay and improve clinical outcomes.