Micro-osteoclast resorption as a characteristic feature of B-cell malignancies other than multiple myeloma

Multiple myeloma (MM) is characterized by the presence of lytic bone lesion and frequent hypercalcaemia. These are due to an excessive osteoclastic resorption in association with a low bone formation, as demonstrated by bone histomorphometry. Conversely, B-cell malignancies other than MM are rarely associated with lytic bone lesion and/or hypercalcaemia. In this study we have analysed quantitative bone histology in 65 patients with B-cell malignancies other than MM at diagnosis: chronic lymphocytic leukaemia (CLL, n = 20), non-Hodgkin's lymphoma (NHL, n = 25), Waldenström's disease (WD, n = 14), hairy cell leukaemia (HCL, n = 6). Fifty patients presented no clinical evidence of increased bone resorption, including no lytic bone lesions radiologically detectable and/or no hypercalcaemia. 80% of these patients (40/50) had increased bone resorption parameter using quantitative bone histology, including 19/29 (65.5%) patients with CLL or WD and 21/21 (100%) patients with NHL or HCL (P less than 0.01). As a control group, seven patients lacking bone marrow involvement on bone sample presented no excessive bone resorption. However, eight patients presented lytic bone lesions and/or hypercalcaemia. All of these patients had increased resorption parameters with high numbers of osteoclasts per surface trabecular bone (mean = 35.3), as opposed to the patients lacking lytic bone lesions and/or hypercalcaemia (mean = 6.6, n = 28) and to normal individuals (mean +/- SD = 3.8 +/- 1.7 and 6.3 +/- 2.6, respectively before and after 60 years). In all the cases, excessive histologic bone resorption was mediated by mononuclear small osteoclasts (mean osteoclast length +/- SD = 27.3 +/- 4.1 as compared to normal range = 35.0 +/- 1.0, P less than 0.001). In different in vitro models, these small mononuclear osteoclasts are considered as progenitors. These data suggest an abnormal osteoclast differentiation in B-cell malignancies other than MM, probably due to differences in the production of local factors acting on bone remodelling.