Analysis of body composition with bioelectrical impedance analysis in different subtypes of pulmonary fibrosis.

Patients with Idiopathic Pulmonary Fibrosis (IPF) often have an unfavourable body composition, characterized by a reduced phase angle (PhA) as an index of cellular health and associated with increased mortality. Little is known about body composition in other subtypes of pulmonary fibrosis (PF). In this single-centre, prospective study, bioelectrical impedance analysis (BIA) was used to assess body composition in patients with PF. In addition, metabolic parameters, lung function, exercise capacity and quality of life (QoL) questionnaires were collected. The fibrosis index (FIBI) was calculated by quantitative computed tomography. A total of 90 patients (57.8% male, mean age 70.8 ± 8.9 years) was analysed. Lung function was mildly impaired with a mean forced vital capacity (FVC) of 76.8 ± 21.4% predicted and mean diffusion capacity for carbon monoxide single breath (DLCO-SB) of 49.5 ± 16.0% predicted. The mean FIBI was 22.5% (SD 10.2). Main diagnoses were systemic autoimmune rheumatic diseases-associated ILD (n = 26, 29.9%), unclassified ILD (n = 19, 21.1%) and fibrosing hypersensitivity pneumonitis (n = 14, 15.6%). 22 patients (24.4%) received steroids and 26 (28.9%) other immunosuppressants. 22 patients (24.4%) experienced ≥ 1 acute exacerbation (AE). The mean body weight was 84.5 ± 18.2 kg with a mean body mass index (BMI) of 28.6 ± 5.7 kg/m2. One patient was underweight, and 31 patients (34.4%) had lost weight during the previous 6 months. BIA showed unfavourable values compared to healthy controls: body fat ↑ (28.9 ± 8.0%), extracellular mass/ body cell mass (ECM/BCM) index ↑ (1.2; IQR 1.0, 1.4), PhA ↓ (4.9 ± 1.0°), cell percentage ↓ (45.4 ± 6.3%) and fat-free mass index ↑ (19.9 ± 2.7 kg/m2). Correlation analyses showed a moderate correlation between PhA and FVC (p < 0.001). No relevant correlations were found between DLCO-SB, walking distance, FIBI, QoL and BIA parameters. Patients with ≥ 1 AE had a significantly worse PhA (p = 0.030). In addition, a sex difference was observed with significantly worse values of PhA for women compared to men (p = 0.036). Patients with PF had an unfavourable body composition with reduced PhA, reduced cell percentage and elevated ECM/BCM index. Significantly lower PhA values were found in patients with ≥ 1 AE and in women. Following longitudinal and interventional confirmation of our results, future research aimed at improving body composition and patient outcomes for those with PF could be conducted.