Osteoporosis associated with mastocytosis confined to bone: report of two cases

Two women, ages 53 and 46, presented with multiple spontaneous vertebral fractures. Serum calcium, 25OHD, 1,25-(OH)2D, PTH, and 24-h urinary calcium were all normal. Bone mineral analysis (BMA) was performed at the junction of the distal third of the radius by single photon absorptiometry. BMA on Patient 1 was 0.68 g/cm2 and on Patient 2 was 0.58 g/cm2, with the normal being 0.70 g/cm2 and 0.77 g/cm2, respectively. In addition to vertebral fractures, x rays of Patient 2 revealed lytic lesions of the tibia and ulna. Bone biopsies revealed osteopenia associated with generalized eosinophilic fibromastocytosis and increased resorption without evidence of increased numbers of osteoclasts. There was no evidence of extraskeletal mast cell involvement. Our observations contribute to the increasing evidence that mast cells play a direct role in the etiology of osteoporosis in certain patients. Possible pathophysiologic mechanisms include mast cell release of heparin, histamine, prostaglandin D2 or other osteolytic substances.