Impact of ETI therapy on bone health, body composition and cardiopulmonary fitness in children with CF

BACKGROUND: Improved survival in cystic fibrosis (CF) has shifted clinical focus toward late complications, including altered body composition, bone health and cardiopulmonary fitness. The effects of Elexacaftor/Tezacaftor/Ivacaftor (ETI) on these outcomes in paediatric patients remain unclear. METHODS: This retrospective cohort study included paediatric CF patients undergoing dual-energy X-ray absorptiometry (DXA) at annual review before and 2 years after ETI initiation. Lean mass index (LMI), fat mass index (FMI), lumbar spine bone mineral apparent density (LS-BMAD) and total body less head bone mineral content (TBLH-BMC) were converted to age and sex-adjusted standard deviation scores (SDS). Spirometry and cardiopulmonary exercise testing (CPET) assessed lung function and cardiopulmonary fitness. A matched CF control group not receiving modulators was included. RESULTS: % predicted decreased in the ETI group (median change -12%, p = 0.0018) alongside reductions in anaerobic threshold (-14%, p < 0.01) and increased breathing reserve (+15%, p < 0.01), controls showed no significant changes. FEV1 % predicted remained stable in both groups. CONCLUSIONS: Despite preserved lung function, ETI treated children exhibited declines in lean mass, trabecular bone density and cardiopulmonary fitness, consistent with deconditioning. DXA and CPET provide important complementary information beyond BMI and spirometry, supporting targeted physical activity and nutritional interventions in ETI treated paediatric CF patients.