Plasma cell leukaemia mimicking acute monocytic leukaemia in the course of multiple myeloma.

We report a case of acute leukaemia occurring early in the course of IgA multiple myeloma. Ultrastructural studies, immunophenotyping and karyotyping were required to identify the origin and clonality of the leukaemic cells. Although ultrastructural examination of the blast cells revealed both monocytoid and plasma cell features, all cells expressed the CD 38 antigen and intracytoplasmic kappa light chains, while karyotyping revealed a clone with numerous abnormalities, leading to the diagnosis of clonal plasma cell disease. The occurrence of leukaemia in multiple myeloma is discussed.