Utility of myeloperoxidase stain in the differential diagnosis of leukemia cutis vs. hystiocitoid Sweet syndrome

Leukemia cutis is defined as a skin infiltration by leukemic cells. The diagnosis of myeloid leukemia cutis (MLC) can represent a challenge, especially in those cases without symptoms of systemic disease. The clinical appearance, histopathological analysis and immunohistochemical profile can be indistinguishable from those observed in cases of hystiocitoid Sweet syndrome (HSS). We present a case of MLC in which the cutaneous affectation was the first sign of the systemic leukemia. In this setting, the myeloperoxidase stain was the clue to rule out the possibility of HSS. We discuss the role and the utility of the myeloperoxidase stain in the differentiation of these two entities.