Bone Mineral Density Response to Long-Term Bisphosphonate Therapy in Fibrous Dysplasia

Fibrous dysplasia of bone is a rare disease related to a genetic mutation in which bone formation at osseous sites is altered. In the last few years, bisphosphonates have become one of the choice drugs to treat this disease. A 26-yr-old woman presented after 6 wk of spontaneous right leg pain owing to a fissure fracture of the right femoral neck. She reported precocious puberty at the age of 2, with diagnosis of McCune-Albright syndrome. Radioisotope bone scanning, radiographic, biochemical, and densitometric studies were performed. Treatment with bisphosphonates was started because bone turnover biochemical markers were abnormal. Oral olpadronate followed by iv pamidronate substantially decreased bone resorption. Bone mineral density (BMD) of total skeleton and subareas was assessed by dual X-ray absorptiometry (DXA) throughout the 5 yr of treatment. At the end of this period, BMD of the total skeleton had increased 6.2%. However, BMD of the areas most affected by fibrous dysplasia, the legs and pelvis, had increased 12.7 and 11%, respectively. Region of interest analysis of individual bones of the legs performed with the total skeleton scan revealed that BMD of the areas most affected by fibrous dysplasia was lower than that of the less affected contralateral bones. During the first 3 yr, treatment with bisphosphonates substantially increased BMD of the right femur and tibia (22 and 28%, respectively). After that, values seemed to stabilize. DXA evaluation of the total skeleton and its subareas was useful to evaluate the efficacy of bisphosphonate treatment. Moreover, the plateau observed in BMD values after 3 yr of treatment suggests that treatment could have been discontinued when the densitometric values stabilized.