Cutaneous involvement as a presenting feature of monocytic leukemia: morphological and immunohistochemical studies

The clinical and pathological findings in a patient with monocytic aleukemic leukemia presenting initially as multiple monoblastic tumors of the skin is described. The patient was a 35-year-old Japanese woman, who had first noticed multiple, asymptomatic, reddish-brown papules on her trunk. Asymptomatic enlargements of several lymph nodes were present in the bilateral cervical and axillary areas. There was no hepatosplenomegaly, sternal tenderness, bruising, or bleeding. The skin and lymph node biopsies were originally interpreted as malignant lymphoma. The diagnosis of acute monocytic leukemia was established when bone marrow involvement was detected. Immunohistochemical observation of the skin eruptions revealed the following: Positive staining with lysozyme was noted in almost half of the infiltrating atypical cells. Most of the infiltrating cells reacted positively with antisera to Leu-M5 and some of them reacted to Leu-M1. The helper T cell antibody, Leu-3a+3b, showed weak positive staining of most infiltrating cells. However, there were no reactions with antisera to Leu-6, Leu-7, Leu-14, CALLA, OKT 6, OKT 8, OKT 16, OKB 19, OKM 14, beta F1, or delta TCS1. OKM 5-positive keratinocytes were observed in some parts of the upper epidermis, although no OKM 5 expression could be detected on any tumor cells. Cytochemistry, immunohistochemistry, and electron microscopy can aid in the diagnosis of monocytic leukemia. This case illustrates the importance of using an expanded panel of monoclonal antisera in certain hematopoietic tumors.