Assessment of Cardiac Sarcoidosis with PET/CT

¹⁸F-FDG PET with CT is an important advanced imaging modality used to assess patients with suspected or known cardiac sarcoidosis (CS). ¹⁸F-FDG PET is indicated for CS work-up in patients with extra-CS and abnormal screening results for cardiac involvement, patients under 60 y old presenting with unexplained high-grade atrioventricular heart block, and patients with suspected CS and idiopathic ventricular arrhythmias. In patients with established CS, serial ¹⁸F-FDG PET can be used to assess response to immunosuppressive therapy and long-term surveillance for reactivation of myocardial inflammation in patients with low-grade or quiescent disease. Patient preparation before ¹⁸F-FDG PET scanning is key in ensuring adequate suppression of physiologic myocardial ¹⁸F-FDG uptake, to maximize the power of the test to detect pathology. Inadequate dietary preparation can cause diffuse or focal-on-diffuse ¹⁸F-FDG uptake in the absence of active inflammation. It is important to assess resting myocardial perfusion, typically with ⁸²Rb cardiac PET. Several different patterns of abnormalities have been reported in patients with CS, including normal myocardial perfusion with focal or patchy ¹⁸F-FDG uptake suggesting myocardial inflammation without scarring; the presence of a myocardial perfusion defect with abnormal ¹⁸F-FDG uptake suggesting myocardial scarring with inflammation; and the presence of a myocardial perfusion defect without ¹⁸F-FDG uptake indicating myocardial scarring without inflammation. Prognostically, the presence of myocardial perfusion defects and abnormal ¹⁸F-FDG uptake has been shown to be an independent predictor of death or ventricular arrythmias. A high myocardial SUV_max in the left and right ventricles has been shown to be an independent predictor of adverse clinical outcomes. Although the diagnostic performance of ¹⁸F-FDG PET has been studied, the reference standard for CS tended to rely on clinical criteria, which may be less sensitive than ¹⁸F-FDG PET at detecting CS. Therefore, the diagnosis of CS should rely on a multidisciplinary team approach involving multimodality advanced imaging, including echocardiography, cardiovascular MR, and ¹⁸F-FDG PET.