Osteoblast stimulation in multiple myeloma lacking lytic bone lesions.

The reasons why some patients with multiple myeloma (MM) do not develop severe bone loss, or even develop sclerotic bone lesions, remain unclear. In order to answer this question at the cellular and tissue level, we evaluated the histological bone condition of 10 patients with MM who never developed lytic bone lesions during the course of their disease (including two patients with sclerotic MM). Myeloma-induced bone changes in the close vicinity of myeloma cells were evaluated by quantitative histology (bone histomorphometry). All 10 patients presented a significantly increased osteoblastic activity. This was associated with an increased bone resorption in seven of the 10 cases. Three patients had a pure osteoblastic presentation. These features were the reverse of the pattern observed in seven patients with lytic bone lesions: increased bone resorption with decreased bone formation. Almost all of these 10 patients showing excessive osteoblastic activity had increased serum bone gla protein levels, a specific marker of bone formation. Finally, 90% of these patients were lambda MM (70% of them were IgG lambda MM), an immunoglobulin subtype previously associated with the sclerotic MM variants. In conclusion, a subset of patients with MM never develop severe bone loss because of the stimulation of osteoblastic activity. These patients belong to the same family as osteosclerotic MM, presenting more frequently the IgG type and lambda subtype.