Measurement of airway inflammation in current smokers by positron emission tomography

Accumulation of activated neutrophilic leucocytes is known to increase uptake of ¹⁸ F-fluorodeoxyglucose (¹⁸ F-FDG) into lung tissue. Available evidence suggests that smokers and subjects with chronic obstructive pulmonary disease (COPD) have neutrophilic inflammation in peripheral airways. The aim of this study was to examine whether current smokers have higher lung tissue uptake of ¹⁸ F-FDG than never-smokers when correcting for air fraction of the lungs.

We prospectively recruited 33 current smokers and 33 never-smokers among subjects referred for diagnosis or staging of cancer, other than lung cancer, with combined positron emission tomography/computed tomography (PET/CT) with ¹⁸ F-FDG. Subjects with focal ¹⁸ F-FDG uptake or focal CT abnormalities in the lungs were excluded. The lungs were segmented in the CT image, and lung density measured. ¹⁸ F-FDG uptake was measured in the corresponding volume and corrected for air fraction.

Lung uptake of ¹⁸ F-FDG, corrected for air fraction, was 12·5 and 8 per cent higher in the right and left lungs, respectively, in current smokers than in never-smokers (P<0·05). Conclusion Abnormal lung tissue uptake of ¹⁸ F-FDG may be masked by reduced lung density if the uptake is not related to air fraction. Increased uptake of ¹⁸ F-FDG in lung tissue in current smokers relative to never-smokers may reflect inflammation in peripheral airways. Measurements of ¹⁸ F-FDG uptake in the lung tissue may be useful for animal and human studies of airways disease in COPD and the relation between airway and systemic inflammation.