Advanced cardiac imaging in cardiac sarcoidosis: current evidence and future directions

Cardiac sarcoidosis (CS) is a rare and complex disease that requires a multidisciplinary approach for diagnosis and treatment. The diagnosis of CS can be confirmed by histological examination of non-caseating granulomas in cardiac or extracardiac tissue, along with supportive clinical and imaging findings. Symptoms are often non-specific, and the yield of endomyocardial biopsy is low due to the patchy nature of cardiac involvement-thus, many cases are not straightforward to diagnose, especially when pulmonary or extracardiac features are absent. Modern non-invasive imaging modalities have unique strengths in assessing the myocardium's structure, function, perfusion, inflammation and fibrosis-abnormalities of all these features exist in CS in varying degrees and can be integrated to assist in the diagnosis. Echocardiography is universally used as the initial imaging test when CS is suspected and provides information on cardiac structure and function, but is limited by inadequate tissue characterisation and differentiation from other infiltrative or restrictive cardiomyopathies. Positron emission tomography (PET) and cardiovascular magnetic resonance (CMR) have good accuracy in diagnosing CS. With current tissue characterisation techniques, such as T1 and T2 parametric mapping, CMR imaging can detect subclinical or early CS. While CMR has better overall prognostic utility for arrhythmic risk and cardiac mortality, fluorodeoxyglucose (FDG)-PET is superior in monitoring disease activity and guiding anti-inflammatory therapy. Hybrid FDG-PET/CMR imaging is a newer, complementary approach that is being increasingly used in centres of excellence. It combines the unique strengths of both modalities, thereby achieving superior sensitivity and specificity.