Fluorodeoxyglucose uptake in brown adipose tissue measured by positron-emission-tomography in chronic lung disease

Abstract

Introduction: Progressive chronic lung diseases often lead to pulmonary cachexia (PC). Here, we assume that the activity of brown adipose tissue (BAT), which is visualised by means of fluorodeoxyglucose (FDG) positron emission tomography (PET), interacts with the weight loss due to PC. Objectives: We aimed to find out whether the BAT activity measured by PET reflects metabolic state and severity of chronic lung diseases. Methods: 104 patients with end-stage chronic obstructive (COPD) and interstitial lung disease (ILD) underwent complete respiratory workup and an FDG-PET/computer tomography (CT) to rule out malignancy within lung transplant evaluation process. Putative supraclavicular BAT regions were identified with CT. Mean standardized uptake values (SUVmean) of predefined volumes of interest were measured. Periumbilical regions with white adipose tissue (WAT) were similarly analysed. These data were normalised to each patient’s liver uptake as reference region. SUV ratios (SUVR) were compared with results from epidemiological and metabolic characteristics (body mass index [BMI]) and pulmonary function tests (FEV1). Group comparisons and Spearman9s correlation coefficients r were calculated. Results: COPD patients expressed an inverse correlation between FDG uptake in putative BAT regions and BMI (P=0.002; r=-0.38). BAT SUVR showed in ILD patients no dependency on BMI. SUVR of periumbilical WAT and supraclavicular BAT positively correlated in COPD and ILD patients (P=0.001, r=0.46) Conclusions: Higher FDG uptake in putative BAT regions is associated with lower BMI in end-stage COPD but not in ILD. This may refer to specific mechanisms in weight loss associated with COPD.