Hidden depletion of fat-free mass and bone mineral density in adults with cystic fibrosis.

BACKGROUND Weight loss is associated with reduced survival in patients with cystic fibrosis (CF). OBJECTIVE We hypothesized that some adult patients with a normal body mass index (BMI) have evidence of hidden fat-free mass (FFM) and bone mineral density (BMD) depletion that is linked to more severe disease. DESIGN Fat mass (FM), FFM, and BMD were determined by dual-energy x-ray absorptiometry (DXA) and by bioelectric impedance in 56 adults in clinically stable condition and 20 age-matched healthy subjects. FM index and FFM index (FFMI) [kilograms per meter squared] of the right arm, leg, and trunk (ratio to height squared) were calculated. Lung function, including the maximum inspiratory pressure (MIP) and sustained MIP (SMIP), physical activity, serum C-reactive protein (CRP) and the number of exacerbations in the previous year were recorded. RESULTS Patients had a lower total FFM than healthy subjects (p < 0.01), while FM was similar. Of the 56 patients, 30 patients had a normal BMI, of which 12 patients had a low FFM (hidden loss) by DXA. The right arm, leg, and trunk FFMI and BMD at hip sites were less in these patients than in those with a normal BMI and normal FFM (all p < 0.01). This group had a lower FEV(1), SMIP, more frequent exacerbations, and greater circulating CRP (all p < 0.05). CONCLUSIONS In adults with CF, apparent or hidden loss of FFM, rather than weight loss, was related to overall disease severity. Hidden depletion of FFM was associated with increased loss of BMD and systemic inflammatory activity.