Multimodality imaging for diagnosis, risk stratification, and treatment monitoring of cardiac sarcoidosis

Cardiac sarcoidosis (CS), with either extracardiac involvement or in isolation, is increasingly recognized. Complications from cardiac involvement are the leading cause of death in patients with sarcoidosis, rendering early detection extremely important given the significant therapeutic and prognostic implications. However, the diagnosis of CS remains challenging due to the lack of a reliable gold standard, largely due to the low sensitivity of traditional endomyocardial biopsy and patchy myocardial involvement. Recent advances in cardiac imaging with [18F] fluorodeoxyglucose positron emission tomography–computed tomography ([18F]FDG PET/CT) and cardiac magnetic resonance (CMR) have provided unprecedented information on the prevalence of CS and have revolutionized the diagnosis and management of CS patients. Abnormal PET/CMR findings are now major criteria in societal guidelines to establish a probabilistic diagnosis of CS. This review provides a brief introduction to CS and a summary of current diagnostic criteria, followed by a review on the current use and strengths of PET/CT and CMR for diagnosis, risk stratification, and treatment response evaluation. CMR is the most robust technique to assess left ventricular function, to detect myocardial fibrosis, and differentiate CS from other cardiomyopathies and has an excellent negative predictive value. On the other hand, [18F]FDG PET/CT is the modality of choice to assess active myocardial inflammation which may be amenable to immunosuppressive treatment as well as to detect extracardiac involvement, to identify potential biopsy sites, and to monitor treatment efficacy. Understanding the complementary value of both techniques is crucial to the optimal utilization of advanced imaging in patients with CS. Lastly, some gaps are identified for future research.