Fibrous Dysplasia in Hospitalized Patients in France: Prevalence and Associated Manifestations from a Health Database

Introduction Fibrous dysplasia (FD)/McCune-Albright syndrome (MAS) is a rare mosaic disorder involving the skeleton and/or extraskeletal manifestations, particularly endocrine features. Population-based estimates of prevalence and incidence are scarce, including in France, and data on associated manifestations mainly derive from specialized centres. This study aimed to estimate the prevalence and incidence of FD/MAS in hospitalized patients in France and to evaluate the frequency of associated manifestations. Methods This retrospective cohort study used the French National Health Insurance Database, to identify all patients hospitalized between 2012 and 2024 with a primary or associated diagnosis of monostotic FD (MFD; ICD-10 M85.0) or polyostotic FD/MAS (PFD/MAS; ICD-10 Q78.1). Prevalence and incidence were calculated for 2024. Associated manifestations were assessed using hospitalization diagnoses and outpatient drug dispensing data. Results Over the 2012–2024 period, 2249 patients were hospitalized in France; 60% had PFD/MAS, 63% were female, and 26% were children. The 2024 prevalence was 5.36 per 1,000,000 inhabitants (95% CI: 4.83–5.94), and the 2024 incidence was 2.58 patients per 1,000,000 inhabitants (95% CI: 2.21–2.99). Regarding associated manifestations, 27% of patients per year received bisphosphonates, 7.4% received phosphate supplements, 3.3% aromatase inhibitors, 8% pituitary treatments and 2.2% antithyroid agents. Conclusion This nationwide study provides the first estimates of the prevalence and incidence of hospitalized FD/MAS in France, although estimates based on hospitalization data likely underestimate the true frequency of monostotic FD. Treatment-based proxies offer valuable insights into associated manifestations. Improved outpatient coding and integration of clinical data are needed to better capture the full spectrum of FD/MAS at the population level.