The eosinophilic fibrohistiocytic lesion of the bone marrow. A mastocellular lesion in bone disease.

Seven patients are described, six with severe osteoporosis and the seventh with osteogenesis imperfecta with moderate osteoporosis. The iliac bone marrow trephine biopsy specimens of all seven showed peculiar infiltrates consisting of elongated mast cells, eosinophils, plasma cells, and varying numbers of lymphocytes. Only one patient exhibited signs of allergy with urticaria pigmentosa; the other six patients had no abnormalities that could be related to a known mast cell disease. The lesions described here are the same as those described in five patients by Rywlin as "eosinophilic fibrohistiocytic lesion in the bone marrow". However, in our methacrylate sections the fibrohistiocytes are shown to be mast cells. Although a relationship with drug hypersensitivity is disputed, the presence of the mast cells and eosinophils suggests an allergic condition.