Eosinophilic fibrohistiocytic lesion of bone marrow associated with monoclonal gammopathy and osteolytic lesions.

We describe a 63-year-old male patient with severe osteoporosis, multiple lytic bone lesions, and monoclonal gammopathy (IgG lambda). Whereas the tentative diagnosis in this case was multiple myeloma, bone marrow trephine biopsies of the iliac crest and from an osteolytic lesion of the tibia both showed a peculiar infiltrate consisting of numerous elongated mast cells, eosinophils, and some plasma cells and lymphocytes. The bone marrow lesions fit the diagnosis of eosinophilic fibrohistiocytic lesion of bone marrow (EFHBM). The patient had no abnormality that could be related to a known allergic disease, and no relationship to drug hypersensitivity could be established. The features of the bone marrow infiltrate and its association with monoclonal gammopathy may suggest a linkage between EFHBM and the monoclonal gammopathy.