[A diagnostically difficult case of hairy cell leukemia with ring-shaped nuclei].

We observed a case of hairy cell leukaemia without splenomegaly and without hairy cells in blood that was difficult to diagnose. Typical hairy cells with cytoplasmic projections were found in hypocellular bone marrow smears rarely whereas atypical mononuclear cells of hairy cell type constituted 70% and 1.5% of them exhibited ring-shaped nuclei. These cells were in 8% positive for tartrate-resistant acid phosphatase. Bone marrow biopsy revealed diffuse infiltration with hairy cells. We reviewed bone marrow smears of 11 other patients with hairy cell leukaemia and we found hairy cells with ring-shaped nuclei in one of them only with a frequency of one promile.