The relation of fat and muscle to emphysema and bronchial wall thickening in smokers

Introduction Differences in body composition in patients with chronic obstructive pulmonary disease (COPD) may have important prognostic value and may provide opportunities for patient specific management. We investigated the relation of thoracic fat and muscle with computed tomography (CT) measured emphysema and bronchial wall thickening. Methods Low-dose baseline chest CT scans from 1031 male lung cancer screening participants from one site were quantified for emphysema, bronchial wall thickening, subcutaneous fat, visceral fat and skeletal muscles. Body composition measurements were performed by segmenting the first slice above the aortic arch using HU-thresholds with region growing and manual corrections. COPD presence and severity was evaluated with pre-bronchodilator spirometry testing. Results Participants had a median age of 61.5 years (58.6–65.6, 25th-75th percentile) and median number of 38.0 pack-years (28.0–49.5); 549 (53.2%) were current smokers. Overall, 396 (38.4%) had COPD (256 GOLD 1, 140 GOLD 2–3). Participants with COPD had less subcutaneous fat, visceral fat, and skeletal muscle (p<0.001 for all). With increasing GOLD stages, subcutaneous (p=0.005) and visceral fat (p=0.004) were higher, and skeletal muscle was lower (p=0.004). With increasing severity of CT-derived emphysema, subcutaneous fat, visceral fat, and skeletal muscle were lower (p<0.001 for all). With increasing CT-derived bronchial wall thickness subcutaneous and visceral fat were higher (p<0.001 for both), without difference in skeletal muscle. All statistical relationships remained when adjusted for age, pack-years and smoking status. Conclusion COPD presence and emphysema severity are associated with lower amounts of thoracic fat and muscle, whereas bronchial wall thickening is associated with fat accumulation.