Increased fluorodeoxyglucose uptake in brown adipose tissue measured by positron emission tomography is associated with pulmonary cachexia in COPD, but not in ILD

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 PC-induced weight loss. We aimed to find out whether the BAT activity measured by PET reflects the metabolic state and the severity of chronic lung diseases.

Methods:

One hundred and four patients with end-stage chronic obstructive (COPD) and interstitial lung disease (ILD) underwent complete respiratory workup and an FDG-PET/computed tomography (CT) to rule out malignancy within the lung transplant evaluation process. Putative supraclavicular BAT regions were identified with CT. Mean standardised 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 a reference region. SUV ratios (SUVR) were compared with results from epidemiological and metabolic characteristics (e.g. body mass index [BMI]) and pulmonary function tests (e.g. FEV₁). Group comparisons and Spearman's correlation coefficients (r) were calculated.

Results:

SUVR in supraclavicular regions were significant higher in woman than in men (P = 0,002). COPD patients showed an inverse correlation between FDG uptake in putative BAT regions and BMI (P = 0.002; r =-0.38). There was no dependency of BAT SUVR on BMI in ILD patients. 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.