Bone Abstracts

Objectives: Fibrous dysplasia is a rare bone and endocrine disorder resulting from somatic activating mutations in GNAS. In the skeleton, proliferation of undifferentiated stromal cells results in osseous lesions that are prone to deformity, fracture, and pain. Lesions may affect one bone or many, and may occur in isolation or in association with hyperfunctioning endocrinopathies, termed McCune-Albright syndrome (MAS). Scoliosis is a potentially serious, even lethal complication; however the prevalence, spectrum, and optimal management have not been established.

Methods: Subjects were evaluated as part of a long-standing natural history in fibrous dysplasia/MAS. Clinical, biochemical and radiographic data were analysed from 138 subjects ranging in age from 2.4–80.

Results: Scoliosis was present in 84 subjects (61%), categorized as mild (Cobb angle >10° and ≤30°) in 65% of subjects, moderate (>30–≤45°) in 13%, and severe (>45°) in 21%. Scoliosis was highly correlated with leg length discrepancy (P<0.002), impaired mobility (P<0.0001), skeletal burden score (P<0.0001), and bone turnover markers. MAS endocrinopathies associated with scoliosis included FGF23-mediated hypophosphatemia (P<0.0004) and hyperthyroidism (P<0.0001). Longitudinal data was available for 69 subjects, including 12 who underwent spinal fusion procedures. In non-surgical subjects, scoliosis was progressive (defined as an increase in Cobb angle >10°) in 31% of subjects (n=18), with a median increase of 18.3° over a 6.2 year period. In 11/12 surgical subjects, spinal instrumentation remained in place after a mean post-operative period of 15 years (range 2.7–38.0). Only one subject required instrumentation removal due to mechanical failure 3 months post-operatively. Serial radiographs were available from 10 surgical subjects, nine of whom showed no progression over a 5.3 year period (range 0.9–14.7 years). Two non-surgical subjects (aged 19 and 41) died from respiratory complications of progressive scoliosis. No fatalities occurred in surgical subjects.

Conclusion: Scoliosis is common in fibrous dysplasia, particularly in patients with leg-length discrepancies and MAS endocrinopathies. Scoliosis is frequently progressive into adulthood. Long-term outcomes from spinal fusion are favorable in most patients. We report the first cases of scoliosis-related fatalities in fibrous dysplasia patients, demonstrating the critical importance of monitoring and treatment for spinal disease in this population.

Disclosure: The authors declared no competing interests.