Diagnosis of cardiac sarcoidosis: a primer for non-imagers

Sarcoidosis is a multisystem granulomatous disorder that can potentially involve any organ. Cardiac involvement in sarcoidosis has been reported in up to 25% of patients based on autopsy and imaging studies. The gold standard for diagnosing cardiac sarcoidosis is endomyocardial biopsy demonstrating non-caseating granulomas; however, this technique lacks sensitivity due to the patchy nature of myocardial involvement. This, along with the non-specific clinical presentation, renders the diagnosis of cardiac sarcoidosis extremely challenging. Difficulties in obtaining histopathologic diagnosis and the advances in imaging modalities have led to a paradigm shift toward non-invasive imaging in the diagnosis of cardiac sarcoidosis. Advances in cardiac imaging modalities have also allowed unprecedented insights into the prevalence and natural history of cardiac sarcoidosis. This review discusses the role of non-invasive imaging for diagnosis, risk stratification, and monitoring the response to therapies in cardiac sarcoidosis. Echocardiography remains the first-line modality due to widespread availability and affordability. Cardiac magnetic resonance imaging (CMR) can be used to study cardiac structure, function, and most importantly tissue characterization to detect inflammation and fibrosis. Fluoro-deoxy glucose positron emission tomography (FDG PET) is the gold standard for non-invasive detection of cardiac inflammation, and it offers the unique ability to assess response to therapeutic interventions. Hybrid imaging is a promising technique that allows us to combine the unique strengths of CMR and FDG PET. Understanding the advantages and disadvantages of each of these imaging modalities is crucial in order to tailor the diagnostic algorithm and utilize the most appropriate modality for each patient.