High-risk and low prevalence disease: Cardiac sarcoidosis and some of its mimics

In this narrative review of cardiac sarcoidosis, based on a literature search using the terms "cardiac sarcoidosis", "tuberculous myocarditis", "Whipple's disease and myocarditis", and"idiopathic giant cell myocarditis", I have defined cardiac sarcoidosis as a disorder which can be diagnosed either by documentation of the presence of sarcoid-related granulomas in myocardial tissue or by documentation of the association of the presence of sarcoid-related granulomas in extracardiac tissue and symptoms such as complete heart block, ventricular tachyarrhythmia, sudden death or dilated cardiomyopathy which are typical of cardiac sarcoidosis. The differential diagnosis of cardiac sarcoidosis includes granulomatous myocarditis attributable to underlying causes such as such as tuberculosis, Whipple's disease, and idiopathic giant cell myocarditis. Diagnostic pathways for cardiac sarcoidosis include biopsy of cardiac and extracardiac tissue, nuclear magnetic resonance imaging, positron emission tomography, and a diagnostic trial of empiric therapy. Problem areas include differentiation between noncaseating granulomatosis attributable to sarcoidosis versus noncaseating granulomatosis attributable to tuberculosis and whether or not the workup of suspected cardiac sarcoidosis should always include evaluation of biopsy tissue by molecular methods for M tuberculosis DNA as well as by mycobacterium tuberculosis culture. The diagnostic significance of necrotising granulomatosis is also unclear. Evaluation of patients on long term immunotherapy should also take due account of the risk of tuberculosis attributable to the use of tumor necrosis factor-alpha antagonists.