Systemic mastocytosis, an unusual cause of osteoporosis.

A 45-year-old patient is described presenting with severe axial osteoporosis. The presence of maculopapular skin lesions and the combination of osteolytic and osteoblastic bone lesions led to the tentative diagnosis of systemic mastocytosis. This diagnosis was confirmed by measurement of urinary histamine metabolites and by bone biopsy showing increased numbers of mast cells and fibroblast-like cells. The importance of these diagnostic procedures in this rare cause of osteoporosis is discussed.