Clinical manifestations and infectious complications of hairy-cell leukaemia.

Hairy-cell leukaemia is an indolent lymphoproliferative malignancy characterized by infiltration of the bone marrow, liver, spleen, and occasionally lymph nodes with a malignant B cell with hair-like cytoplasmic projections. This involvement leads to splenomegaly with secondary consumption of red cells, platelets and neutrophils as well as other complications of an enlarged spleen, including infarction-or-rarely rupture. The common haematological complications of anaemia, neutropenia and thrombocytopenia are due not only to the enlarged spleen but probably also to hairy cells in the bone marrow inducing cytokine-mediated suppression of haematopoiesis. Hepatic involvement, although frequent, only occasionally leads to liver dysfunction. Infections are a major cause of morbidity and mortality in patients with hairy-cell leukaemia, presumably owing to neutropenia and monocytopenia in these patients. The infections seen may be due to unusual pathogens, including Mycobacterium and Listeria. Autoimmune disease, including polyarthitis and vasculitis, occurs frequently and does not correlate with the severity of the disease. Other rare complications include bone involvement, meningitis and ascites. A wide range of secondary malignancies have been reported in patients with hairy-cell leukaemia, but it is still unclear whether the incidence is increased and whether they are related to the disease or treatment.