Skeletal mastocytosis.

AIMS: To characterise the condition of skeletal mastocytosis, an uncommon cause of apparently "idiopathic" osteoporosis.
METHODS: Transiliac crest biopsy specimens submitted over a period of five years were examined for nodular accumulation of mast cells. The cases were reviewed histologically and clinical follow up was obtained from hospital notes.
RESULTS: Six cases of mastocytosis occurring in bone biopsy specimens submitted to our department were identified. Four patients presented initially with vertebral collapse and the other two were known to have extraskeletal mast cell disease at presentation. On clinical review of the four patients with vertebral collapse, one was found to have urticaria pigmentosa. This patient died from his mastocytosis, whereas the three patients without evidence of extraskeletal disease remain alive and well. Histological examination showed that patients with the poorer clinical outcome had severe peritrabecular fibrosis as well as mast cell nodules; those with prolonged disease-free survival had nodules without peritrabecular fibrosis.
CONCLUSION: There is a form of mastocytosis which presents clinically as "idiopathic" osteoporosis. Clinically it does not have the same prognostic implications as skeletal disease in "malignant mastocytosis", running a much more benign course.