Haematology Grand Rounds. Hairy cell leukaemia masquerading as malignant lymphoma.

Pancytopenia with massive splenomegaly, minimal lymphadenopathy and circulating atypical lymphoid cells with cytoplasmic projections characterize the lymphoproliferative disorder known as hairy cell leukemia, or leukaemic reticulo-endotheliosis. Many of the features of hairy cell leukaemia are shared with a malignant lymphoma of the B-cell type, from which it can be distinguished on a number of criteria, including histological examination of bone marrow, lymph nodes, liver and spleen. Recognition that this syndrome is not homogeneous is important, since in the B-cell tumour the clinical course is progressive, requiring chemotherapy which is usually effective; the disease is indolent in leukaemic reticulo-endotheliosis and drug treatment may actually shorten survival. The patient presented illustrates the ease with which this diagnostic error can arise, and the features separating these two unusual entities are reviewed.