Bone mineral density in children and adolescents with cystic fibrosis: a longitudinal study.

Background: Adults with cystic fibrosis (CF) show a higher rate of osteoporosis compared to healthy adults. Achieving proper adult bone mass is a process starting in childhood. We aimed to evaluate the prevalence, course in time and risk factors for decreased bone mineral density (BMD) in youth with CF.

Methods: Anthropometry, dual-energy X-ray absorptiometry (DXA), and endocrine data were collected in 106 children and adolescents with CF. BMD Z-scores were adjusted for height (BMD Z-score). At risk and low BMD were defined as Z-scores ≤ -1 and ≤ -2, respectively. Multivariable analyses were performed for change in BMD Z-scores in 65 patients with a second DXA available.

Results: At baseline, overall normal median (IQR) BMD Z-scores were found (-0.02 (-0.85 - 0.55) and -0.01 (-0.72 - 0.82) for lumbar spine (LS) and total body less head (TBLH) respectively). In 6.6 % and 2.8 % of patients low BMD Z-scores were found for LS and TBLH. At follow-up, significant decreases in BMD Z-scores at both LS and TBLH were identified (p = 0.003 and p < 0.001). The decrease in TBLH BMD Z-scores was higher in boys than girls (p < 0.001). New onset of CFRD (β = -0.493, p = 0.002) was a negative predictor for the change in TBLH BMD Z-score.

Conclusion: Most children and adolescents with CF have normal BMD Z-scores. However a significant decrease in BMD Z-scores over time is already seen during childhood, especially in boys and in those with newly onset CFRD.