Bone health after 3 years of ETI therapy: a real-world study from the Danish cystic fibrosis cohort

BACKGROUND: Malnutrition, inflammation, limited exercise, and low muscle mass increase the risk of cystic fibrosis (CF) bone disease (CFBD). Additionally, dysfunction of the CF transmembrane conductance regulator (CFTR) directly affects bone-forming cells. Elexacaftor/Tezacaftor/Ivacaftor (ETI) could influence these aspects. We examined the impact of ETI on bone health in Danish people with CF.

METHODS: This nationwide cohort study evaluated changes in bone status in adults with CF after ETI treatment. Dual energy X-ray absorptiometry (DXA) was used to assess bone mineral density Z-scores in lumbar spine, femoral neck, and total hip. To assess calcium metabolism, plasma levels of vitamin D, calcium, and parathyroid hormone (PTH) were evaluated. Data were collected from 2 years pre- to 3.5 years post-ETI initiation, comparing pre-ETI levels with 1-, 2- and 3-year post-ETI measurements. Data were analyzed using linear mixed effects regression models and subgroup interaction analyses.

RESULTS: 197 Danish adults with CF were included in the study, contributing 435 DXA scans. Mean change from pre-ETI period (95%CI) in femoral neck and total hip Z-scores showed a decrease by year 3 of -0.16 (-0.31; -0.01; p=0.04) and -0.15 (-0.30; <0.01; p=0.05), respectively, while lumbar spine showed a slight increase of 0.13 (-0.05, 0.31; p=0.15). Vitamin D levels initially decreased but subsequently increased by 8.9 nmol/L (4.5-13.3; p<0.01) by year 3 as compared to pre-ETI levels. Calcium and PTH levels remained stable.

CONCLUSION: After 3 years of ETI treatment in Danish adults with CF, no clinically significant changes in bone health or calcium metabolism were observed.