Extramedullary diseases as presenting features of aleukemic acute monocytic leukemia

We present a case of acute monocytic leukemia presenting with extramedullary disease clinically resembling lymphoma. A 36 year-old man presented with arthralgia and was found to have skin eruption, nasopharyngeal mass, hepatosplenomegaly and superficial lymphadenopathy. The biopsies of those lesions as well as bone marrow revealed infiltration of CD45 positive large atypical cells and were interpreted as malignant lymphoma. At that time blood film showed leuko-erythroblastic picture, but no atypical cells were noted. He was treated with CHOP followed by VEPA chemotherapy and achieved partial remission. Four months later headache and double vision occurred with the same atypical cell in the cerebrospinal fluid. The cells were identified as monoblasts by cytochemistry and immunophenotype. The diagnosis of aleukemic acute monocytic leukemia was made and its CNS involvement was successfully treated with chemotherapy with DHAP and intrathecal MTX. However, two months later, blasts finally appeared in the peripheral blood and the patient died of multiorgan failure eight months after presentation. The blasts were positive for T cell markers (CD2, 4, 8) and NK marker (NKH-1) as well as monocytic markers. This finding, together with those by other investigators, may indicate the association between these immunophenotypes and extramedullary manifestations of acute monocytic leukemia.