18F-FDG PET patterns and BAL cell profiles in pulmonary sarcoidosis

Bronchoalveolar lavage (BAL) and F-18-fluorodeoxyglucose (F-18-FDG) PET can both demonstrate sarcoid activity. To assess whether metabolic activity imaged by F-18-FDG PET represents signs of disease activity as reflected by BAL, F-18-FDG PET patterns were compared with BAL cell profiles. In this retrospective analysis, 77 newly diagnosed pulmonary sarcoidosis patients underwent BAL and F-18-FDG PET. Based on F-18-FDG PET, patients were diagnosed with exclusively mediastinal/hilar activity (group A) and activity in the lung parenchyma (group B). Per group, BAL lymphocytes (%), CD4/CD8 ratio, CD103(+)CD4(+)/CD4(+) ratio and neutrophils (%) were compared with the extent of metabolic activity expressed as the maximum standardized uptake value (SUVmax). Additionally, SUVmax and BAL parameters per radiographic stage were analysed. Overall, the SUVmax in the lung parenchyma correlated with neutrophils and SUVmax of the mediastinum/hila correlated with the CD4/CD8 ratio. In both groups, a significant, negative correlation between the SUVmax of the mediastinum/hila and the CD103(+)CD4(+)/CD4(+) ratio was found. In group B, the SUVmax of the mediastinum/hila correlated with the CD4/CD8 ratio, while the SUVmax in the lung parenchyma correlated with the CD103(+)CD4(+)/CD4(+) ratio and neutrophils. Significant differences were found in the SUVmax, CD4/CD8 ratio, CD103(+)CD4(+)/CD4(+) ratio and neutrophils between the radiographic stages. The SUVmax of the lung parenchyma was positively related to the radiographic stage, while the SUVmax of the mediastinum/hila and CD4/CD8 ratio were inversely related. F-18-FDG PET correlates with the CD4/CD8 ratio and neutrophils, suggesting that F-18-FDG PET represents this specific cell profile in BAL. High SUVmax values of the lung parenchyma may therefore correlate with more severe parenchymal involvement, particularly when accompanied by a low SUVmax of the mediastinum/hila.