18F-FDG PET in sarcoidosis

Sarcoidosis is a granulomatous disease of unknown cause. It can affect all organs although the lungs, eyes and skin are most frequently involved. The presence of active disease is currently based on several parameters such as symptoms, clinical findings, the serum markers angiotensin converting enzyme (ACE) and soluble interleukin-2 receptor (sIL-2R), chest radiography, pulmonary function tests (PFT) and bronchoalveolar lavage (BAL). However, a gold standard for the assessment of active disease is unavailable. Therefore, the use of ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) PET in the assessment of sarcoidosis activity was evaluated and compared with the aforementioned markers for active disease. The following conclusions may be drawn from the studies described in this thesis: Compared to 67Ga scintigraphy, ¹⁸F-FDG PET is more sensitive in assessing sarcoidosis activity and demonstrates a higher inter observer agreement ¹⁸F-FDG PET appears more sensitive than genotype corrected ACE and sIL-2R in determining the presence of active disease The degree of metabolic activity in the pulmonary tract imaged by ¹⁸F-FDG PET and expressed as maximum standardized uptake value (SUVmax), correlates with the CD4+/CD8+ ratio and neutrophils in BAL In untreated patients, the absence of parenchymal activity imaged by ¹⁸F-FDG PET correlates with stable pulmonary function tests after one year, while diffuse parenchymal activity predicts a decrease in diffusion capacity of the lung for carbon monoxide (DLCO) In patients with diffuse parenchymal activity imaged by ¹⁸F-FDG PET, pulmonary function tests improve by using immunosuppressive therapy, suggesting that ¹⁸F-FDG PET presents the possible improvement that can be achieved In chronic sarcoidosis patients treated with infliximab, changes in ¹⁸F-FDG PET correlate with the clinically observed response In chronic sarcoidosis patients, the change in SUVmax of the lung parenchyma correlates with the change in vital capacity (VC) attained by infliximab therapy An ¹⁸F-FDG PET based classification system of sarcoidosis incorporating four major phenotypic presentations is reproducible