Multiple myeloma and hairy cell leukemia: a rare association or coincidence?

Hairy cell leukemia (HCL) and multiple myeloma (MM) are well-defined entities with distinctive clinical and pathological features. Although most cases of HCL and MM fit their classic descriptions, more recent studies have revealed that their clinical and morphological boundaries may not only overlap but a transformation of HCL into MM could also occur. We report another case of HCL followed by the development of MM after 9 years. He also developed hemarthrosis of his right ankle at the time of diagnosis of MM. PCR analysis of DNA extracted from the bone marrow aspirate was negative for the presence of a monoclonally rearranged immunoglobulin heavy chain gene. Immunophenoytping revealed no evidence of HCL. There are several possible explanations for the development of MM in HCL patients, such as the coexistence of separate disease entities or different clinical and morphologic phases of a single disease entity. An accurate diagnosis of HCL or MM is critical because of differences in their treatment. Hemarthrosis in this patient may also have been the first manifestation of MM, a feature of MM which has rarely been reported.