Objectives To investigate bone involvement in a large cohort of systemic mastocytosis (SM) patients, and evaluate the efficacy of bisphosphonate therapy.

Patients and Methods From 2000 to 2004, 75 patients with SM according to WHO criteria underwent skeletal x-rays and bone mineral density (BMD) assessment. Sequential BMD assessments were performed in nine patients treated with bisphosphonate (mean follow-up 65 months).

Results 37 patients (49%) had bone involvement according to both x-rays and BMD evaluations: osteoporosis (23 patients, 31%, mean lumbar spine T score: −3 SD), with vertebral fracture (13 patients, 17%), axial skeleton osteosclerosis (six patients, 8%), mixed patterns (three patients), osteopenia with pre-existing fractures (four patients) and focal osteolytic lesion (one patient). Blood count abnormalities were associated with osteosclerosis (p=0.005). In nine patients with osteoporosis and bisphosphonate therapy, mean lumbar spine BMD increased from 0.83 to 0.92 g/cm² (+11.1%; ie, +2.05% per year) without recurrence of vertebral fracture.

Conclusion Half of adult patients with SM have bone involvement. Osteoporosis is the most prevalent bone manifestation in SM (31%). Bisphosphonate therapy seems efficient to improve lumbar spine BMD during SM-related osteoporosis. Spine x-ray and BMD should be performed in all SM patients to detect those who may benefit from anti-osteoporotic therapy.