Longitudinal Changes in Bone Mineral Density in Adults with Cystic Fibrosis.

Background: Improved survival in people with cystic fibrosis (pwCF) presents new complexities of care, including CF-related bone disease, a common complication in older pwCF. The trajectory of bone loss with age in this population remains unclear. The objective of this study was to estimate the average rate of change in bone mineral density (BMD) in adults with CF.

Methods: This retrospective study included adults with CF, aged 25-48 years, followed between January 2000 and December 2021. Subjects with at least one dual-energy X-ray absorptiometry (DXA) scan were included. Scans obtained post-transplantation, after the initiation of bisphosphonates or cystic fibrosis transmembrane conductance regulator (CFTR) modulator therapy were excluded. The primary outcome was BMD (g/cm2) at the lumbar spine (LS) and femoral neck (FN). A linear mixed-effects model with both random intercept and random slope terms was used to estimate the average annual change in BMD.

Results: A total of 1502 DXA scans in 500 adults (average age 28.4y) were included. There was a statistically significant annual decline in BMD of -0.008 gm/cm2/year (95% CI -0.009, -0.007) at the FN and -0.006 gm/cm2/year (95% CI -0.007, -0.004) at the LS. Relative to BMD at age 25, there was a -18.8% decline at the FN by age 48 years and a -11% decline at the LS. Pancreatic insufficient (PI) subjects had a faster rate of decline in BMD compared to pancreatic sufficient (PS) subjects. After adjusting for markers of disease severity, the annual rate of decline remained significant.

Conclusions: Individuals with CF experience bone loss at an age when it is not anticipated, thereby entering early adulthood, where further bone loss is inevitable especially with the decrease in estrogen during menopause, with suboptimal BMD. As the CF population ages, it will become very important to consider interventions to maximize bone health.