Specific skin infiltration as first sign of chronic myelomonocytic leukemia with an unusual phenotype.

A patient who had a plaque on his forehead as the first sign of chronic myelomonocytic leukemia (CMML) is described. Histologic studies, which formerly led to the misdiagnosis of non-Hodgkin's lymphoma, revealed CMML with an unusual phenotype. This represents a rare type of CMML for the following reasons: (1) specific cutaneous involvement is rarely the first sign of CMML; (2) the unique phenotype was detected by immunohistology on lesional skin, specifically, the leukemic infiltrate was CD4-positive and notably negative for CD15, the pan myeloid/monocytic marker.