Skeletal complications in hairy cell leukemia: diagnosis and therapy.

We identified eight patients with skeletal complications associated with hairy cell leukemia (HCL). The median time from diagnosis of HCL to the diagnosis of skeletal complications was 20 months (range, 0 to 93). All patients complained of pain and all but one lesion were located in the axial skeleton, primarily the proximal femur. Lytic lesions were seen on radiographic examination in all but one patient, and one patient additionally had multiple osteoporotic vertebral compression fractures. Radionuclide technetium bone scan was abnormal in all patients examined. Although the peripheral blood counts were variable (only two patients had a leukemic phase of the disease), all patients examined had a hypercellular bone marrow biopsy with hairy cells comprising at least 90% of the hematopoietic elements. The skeletal abnormalities responded well to local radiation therapy. Seven patients were begun on systemic therapy with interferon alpha-2b after the diagnosis of the skeletal lesion. Four of five evaluable patients had a partial hematological response and a substantial improvement in the degree of hairy cell infiltration of the bone marrow. None of these patients has had a recurrence of skeletal complications at a median follow-up time of 29 months. One patient failed to respond hematologically and developed additional bone lesions after 1 year of treatment. Another patient developed a new skeletal lesion 3 months after the cessation of interferon therapy at which time the bone marrow was essentially packed with hairy cells. This retrospective study indicates that bone involvement is a rare complication of HCL and is associated with a high tumor burden in the bone marrow. In addition to local radiation therapy, systemic treatment with interferon should be considered.