Aleukaemic leukaemia cutis presenting as a benign-appearing eruption

A 68-year-old Caucasian male presented with a 5-week history of a widespread pruritic papular eruption. Histology from a papule on the left shoulder showed a dense dermal infiltrate of large mononuclear cells which were positive for leucocyte common antigen, KP1 and PGM1, with an MIB-1 proliferating fraction of 40%, diagnostic of acute monocytic (M5) leukaemia cutis. Full blood count revealed pancytopaenia but no blasts. Bone marrow aspirate showed reduced red cell precursors and 10% blasts, consistent with myelodysplastic syndrome (refractory anaemia with excess blasts). The patient was managed with a 3 unit transfusion of packed red cells, after which his skin eruption resolved within 6 weeks and his peripheral blood counts returned to normal. No chemotherapy was administered. In conclusion, leukaemia can present in the skin, the eruption may be nonspecific and it may precede systemic involvement by either myelodysplastic syndrome or acute leukaemia.