Bone lesions in systemic mastocytosis: Bone histomorphometry and histopathological mechanisms.

Osteoporosis is considered the most frequent skeletal manifestation of systemic mastocytosis (SM). We performed a retrospective analysis of sixty patients (37 males and 23 females) who underwent a bone biopsy in the assessment of SM or in the assessment of unexplained bone fragility. Thirty-three had simultaneously a bone marrow biopsy with a Jamshidi's needle; this sample was used for immunohistochemical analysis (tryptase, c-KIT. CD20, VCAM-1). Bone biopsy was realized in 42 cases in the assessment of SM to provide histologic proof of the disease and in 18 cases in the assessment of unexplained bone fragility and surprisingly revealed a SM. An increased bone turnover was observed in patients with SM with elevated eroded surfaces, osteoclast number and bone formation rate. In addition to nodules of mast cells (MC), a high number of MC was directly apposed on the trabeculae, affixed on the osteoblasts or the lining cells. The VCAM-1 adhesion protein recognizing α4β7 and α4β1 integrins may be a candidate to explain this particular adherence. One third of the bone marrow biopsies did not exhibit MC nodules or MC infiltration and led to a false negative diagnosis for SM. SM can be discovered in the assessment of fracture or osteoporosis. Transiliac bone biopsy allows for the diagnosis of the disease more accurately than bone marrow biopsy; it also provides a histomorphometric analysis of bone remodeling.