Refractory macrophage activation syndrome in the setting of adult‐onset Still disease with hemophagocytic lymphohistiocytosis detected on skin biopsy treated with canakinumab and tacrolimus

: A 19-year-old Caucasian female with adult-onset Still disease (AOSD) presented for evaluation of an acute clinical decompensation and atypical annular papules and plaques with purpura on the lower extremities. A punch biopsy demonstrated histiocytes with engulfed degenerated erythrocytes and lymphocytes, consistent with hemophagocytic lymphohistiocytosis (HLH). HLH, clinically referred to as macrophage activation syndrome, is a rare complication of AOSD and is life-threatening. Relevant clinical, laboratory, and histologic features of this diagnosis are reviewed.