Body composition and energy expenditure of patients with Fibrodysplasia Ossificans Progressiva

Fibrodysplasia Ossificans Progressiva (FOP) is a rare bone disease causing progressive immobilization due to heterotopic ossification in fibrous tissues. Compromised food intake and weight loss are often seen in FOP patients, but the effects on body composition, energy expenditure and metabolic markers remain unclear. BMI, fat percentage and fat-free mass (FFM) were extracted from DXA scans in a retrospective cohort of 15 FOP patients and compared to calculated reference values. Additionally, resting energy expenditure (REE) and body composition were prospectively evaluated in 11 patients using indirect calorimetry and bioelectrical impedance (BIA). Disease severity was assessed with the cumulative analogue joint involvement scale (CAJIS), and metabolic markers were analyzed. Among 18 different patients of both cohorts combined, six had low BMI (<18.5), including four being severely underweight (BMI < 17). Median BMI was significantly lower in patients with severely restricted mouth opening (17.3 vs. 23.6 kg/m², P = .001). FFM measured by DXA and BIA was significantly lower, and fat percentage higher, than reference values, particularly in those with higher CAJIS scores. Measured REE was lower than predicted by the WHO formula in all patients (1211 versus 1437 kcal/day, P = .003). Creatinine was reduced in 45% of patients, whereas LDL was elevated in 22%. Underweight status is prevalent in FOP, especially in patients with severely restricted mouth opening. Lower FFM, REE and creatinine suggest loss of muscle mass, probably due to immobilization. Individual nutritional and physiotherapeutic interventions should be guided by measured BMI, body composition, and REE, with a primary focus on preserving muscle mass.