Fibrous dysplasia of bone

Fibrous dysplasia of bone is a disease that can involve one or several bones and is characterized by bone deformities, pain and iterative fractures. Some patients can present with endocrine dysfunction (generally precocious puberty) and cutaneous cafe-au-lait spots. Some complications, such as nerve compression and malignant transformation, are uncommon. Many patients can, however, be asymptomatic. Diagnosis relies on X-ray examination and pathology. Prognosis is assessed by X-rays and markers of bone remodelling. Several breakthroughs in the understanding of the pathophysiology have been made in the past 10 years. It is now recognized that fibrous dysplasia is caused by a somatic activating mutation of the Gsx subunit of protein G, resulting in an increased cAMP concentration and thus in abnormalities of osteoblast differentiation, these osteoblasts producing abnormal bone. There is also an increase in interleukin-6-induced osteoclastic bone resorption, which is the rationale for treating these patients with bisphosphonates. In the past 10 years, the bisphosphonate pamidronate has been used by infusion for fibrous dysplasia (two courses per year), with good results with respect to pain and, in about 50% of patients, the refilling of osteolytic lesions.