As discussed above, the nonspecific findings often encountered on endomyocardial biopsies pose a diagnostic challenge. While nonspecific findings such as interstitial fibrosis, necrosis, and inflammation may support the diagnosis of cardiac sarcoidosis, they are also found in a number of broad differential diagnoses.[11,15,16] Entities that should be considered and ruled out include giant cell myocarditis, tuberculous myocarditis, fungal myocarditis, systemic lupus erythematosus, and rheumatoid nodules. In particular, idiopathic giant cell myocarditis, which is characterized by an inflammatory infiltrate of eosinophils, lymphocytes, macrophages, and giant cells associated with myocyte necrosis, can resemble sarcoidosis on an endomyocardial biopsy (Image 1). While the key distinguishing feature in giant cell myocarditis vs cardiac sarcoidosis is the lack of granuloma formation, occasional granuloma formation has been observed in 5% to 10% of giant cell cardiomyopathy cases. Additional distinguishing features include the presence of eosinophils in giant cell cardiomyopathy vs cardiac sarcoidosis. Fibrosis is also more common in cardiac sarcoidosis. Clinical context, imaging, and histologic special stains, as discussed above are also important to rule out infectious and autoimmune differential diagnoses.
Due to the low sensitivity of endomyocardial biopsies for diagnosis of cardiac sarcoidosis, the Japanese Society of Sarcoidosis and Other Granulomatous Disorders released guidelines for diagnosis of cardiac sarcoidosis that incorporate histologic, radiologic, and clinical features.[4,24] Histologic criteria include definitive demonstration of nonnecrotizing granulomatous inflammation in endomyocardial biopsies, as discussed above. Without a diagnostic endomyocardial biopsy, a patient with known extracardiac sarcoidosis may be diagnosed with cardiac sarcoidosis by fulfilling of at least two major criteria or at least one major criterion plus greater than two minor criteria. Major criteria include advanced atrioventricular block, thinning of the basal interventricular septum, positive gallium-67 uptake in the heart, or depressed ejection fraction.[4,24] Minor criteria include abnormal echocardiogram or electrocardiogram findings, perfusion defects on nuclear imaging, delayed enhancement of the myocardium by gadolinium-enhanced cardiac MRI, or endomyocardial biopsy showing interstitial fibrosis or monocyte infiltration of at least moderate grade.[4,24] The Heart Rhythm Society (HRS) also released a similar expert consensus statement in 2014 based on the Japanese guidelines for clinical diagnosis of cardiac sarcoidosis. The HRS consensus statement also takes into consideration responsiveness to corticosteroid or immunosuppressive therapy.
Am J Clin Pathol. 2020;153(3):294-302. © 2020 American Society for Clinical Pathology