Bridging the Divide: Divergent Diagnostic Philosophies and Practice Pathways for Cardiac Sarcoidosis between Japan and North America.

Cardiac sarcoidosis (CS) is an increasingly recognized inflammatory cardiomyopathy that can present with ventricular arrhythmias and progressive heart failure (HF). Despite advances in various imaging modalities, notable regional differences persist in how CS is suspected, diagnosed, and managed. In Japan, where CS has long been a clinical priority, and where advanced imaging is widely accessible, screening and diagnostic pathways are often applied earlier in the disease course. In contrast, in many North American and Western settings, CS is frequently identified after presentation with advanced cardiomyopathy or arrhythmic complications. The most profound divergence lies in the diagnostic framework. The Japanese Circulation Society (JCS) guidelines emphasizes early recognition of clinically diagnosed forms of cardiac involvement in patients with known systemic sarcoidosis and without the requirement of invasive endomyocardial biopsy. The JCS guidelines also formally recognize "clinically isolated CS" as a clinically defined entity confined to the heart. In contrast, the U.S. criteria prioritize specificity, requiring histological proof from any organ for a definitive diagnosis. This divergence propagates downstream discrepancies in risk stratification and therapeutic strategies. In this review, we discuss the original research underpinning these frameworks and the need for international harmonized research efforts to better define this entity and inform future diagnostic and management strategies.