Fibrous dysplasia (FD) of bone is a rare but potentially severe
bone disease that often entails fractures,
deformities, and bone
pain. An activating mutation of the alpha subunit of Gs
proteins leads to differentiation abnormalities of the osteoblastic lineage, which are responsible for development of fibrous tissue in the medulla and increased osteoclastic activity. This increased
bone resorption has been the rationale to use
bisphosphonates in our center since 1988. So, we have analyzed the largest series, so far, of patients treated with the
bisphosphonate pamidronate and sought predictors of response to treatment. We have treated 58 patients (41 adults and 17 under 18 years of age) with FD in an open study, using intravenous (IV)
pamidronate 180 mg every 6 months and
calcium and
vitamin D supplements, in combination with oral
phosphate and
calcitriol in patients with FD who also had renal
phosphate wasting. Patients were followed up with biannual visits, for an average 50 months, with
pain assessment, annual radiographs of affected bones, measurement of
biochemical markers of bone turnover, and annual bone mineral density measurements in the case of affected hips. We found that
pain intensity significantly decreased with treatment in the 44 patients who had bone
pain at baseline,
biochemical markers of bone turnover were significantly reduced, and about 50% of patients had improvement of bone lesions on radiographs, evidenced by filling of osteolytic lesions and/or cortex thickening. Bone mineral density was substantially increased in the 12 patients who had hip FD. There was no significant clinical or
biological predictor of positive radiographic response to
pamidronate treatment. Long-term treatment with
pamidronate was safe, in particular among the 12 patients who were followed up for more than 8 years. Despite the lack of a control group, our results suggest that intravenous
pamidronate improves radiological aspect in half of the patients with FD, decreases bone turnover, and may decrease
pain intensity.