Endocrine Abstracts

Fibrous dysplasia of bone (FD) – a rare disease due to osteoblastic lineage differentiation defects – is associated with bone pain, fracture and bone deformity, but few therapeutic options are available. Antiresorptive agents such as bisphosphonates may be of interest because there is evidence of increased osteoclastic activity in FD bone lesions, even if the disease is due to an osteoblastic defect.

We have reviewed published data on the treatment of FD with bisphosphonates (pamidronate, alendronate, zoledronic acid), calcium, vitamin D and phosphorus.

Pamidronate therapy, given intravenously every 6 months at the dose of 180 mg in adults, relieved bone pain, decreased bone resorption and improved the radiological aspect (filling of lytic lesions and/or thickening of cortices) in about 50% of patients. Bone mineral density in affected sites was also significantly increased after pamidronate treatment. Those results have been obtained only in open studies, without controls, by several research groups. In a series of 9 patients on long-term pamidronate treatment, but resisting to this medication and switched to intravenous zoledronic acid, no substantial improvement was observed. There is some biological rationale supporting the use of calcium and vitamin D in patients with deficiency, to improve FD lesions by limiting secondary hyperparathyroidism. Phosphorus supplementation may prevent mineralization defects in those patients who have both FD and renal phosphate wasting. But we are lacking clinical evidence for the efficacy of such supplements. There are two ongoing clinical controlled trials testing the efficacy of alendronate or risedronate compared with placebo.

Bisphosphonates treatment reduces increased osteoclastic activity in FD and probably improves bone pain, but their use should be better studied in ongoing randomized controlled trials. Supplements in calcium, vitamin D and phosphorus may be useful.