Continuous fat-free mass decline in COPD: fact or fiction?

Patients with chronic obstructive pulmonary disease (COPD) generally have lower fat-free mass (a surrogate marker of skeletal muscle mass) compared with their healthy peers [1, 2], and this is associated with decreased functional capacity [3], the presence of other comorbidities (e.g. osteoporosis and renal impairment) [4] and increased mortality risk [5]. To date, longitudinal observational studies have shown no difference in the mean decline in fat-free mass over time between COPD patients and non-COPD control subjects [6, 7]. However, it remains unknown whether and to what extent a subgroup of COPD patients suffer continuous loss of fat-free mass. We hypothesised that COPD patients have 1) a higher prevalence of continuous fat-free mass decline, and 2) that this subgroup has a steeper decline of fat-free mass compared with a non-COPD control group with a continuous fat-free mass decline. We tested this hypothesis in the ECLIPSE (Evaluation of COPD Longitudinally to Identify Predictive Surrogate Endpoints) study, which had a 3 year follow-up period.