Bone mastocytosis. A report of nine cases with a bone histomorphometric study.

Bone mastocytosis is characterized radiographically in some patients by diffuse osteosclerosis and in others by demineralization. The reason for these apparently conflicting bone features is unknown. Bone remodeling and marrow mastocytosis infiltration were studied in nine cases of mastocytosis with bone marrow involvement. Six men, ranging from 42 to 78 years of age, and three women, 43, 55, and 73 years old, comprised the series. Two patients had severe and diffuse osteosclerosis. Seven had diffuse demineralization, with crushed vertebrae in four, suggesting common osteoporosis. In three of the seven, cutaneous mastocytosis was absent. Bone biopsies were undecalcified and stained with toluidine blue. In the seven patients with demineralization, the number of marrow mastocytes was increased (154 +/- 24 versus 2 +/- 0.5/mm2 in normal postmenopausal osteoporosis). Mastocyte nodules covering 1-9% of the marrow area were present in all seven patients. These patients showed a significant increase in remodeling; bone formation rate was increased, coupled with a decrease in mean wall thickness. Concomitantly, osteoclast surfaces were increased, with an increased amount of bone resorbed. The two patients with diffuse osteosclerosis had a markedly different histology; mast cell infiltration was dramatically increased (mastocyte count greater than 1000/mm2) with diffuse marrow fibrosis. Bone volume was increased as well, and most of the bone was woven with an intratrabecular mineralization defect. High bone remodeling and decreased osteoblast activity can explain bone loss in mastocytosis with demineralization. Mastocytosis with osteosclerosis is characterized by a more extensive marrow mast-cell infiltration and fibrosis.