Myocarditis and endomyocardial biopsy: achieving consensus diagnosis on 100 cases

Area of Science:

• Cardiovascular Pathology
• Histopathology
• Immunohistochemistry

Background:

• Myocarditis diagnosis relies on histopathology benchmarks like the Dallas Criteria and European Society of Cardiology criteria.
• The European Society of Cardiology criteria incorporate immunohistochemistry for CD3+ T cells and CD68+ macrophages.
• Consistency in applying these criteria for myocarditis diagnosis on endomyocardial biopsy (EMB) is not well understood.

Purpose of the Study:

• To assess the consistency and diagnostic confidence of international cardiovascular experts in diagnosing myocarditis from endomyocardial biopsies.
• To evaluate the challenges in diagnosing myocarditis, particularly borderline cases, using existing histopathological criteria.

Main Methods:

• 100 digitally scanned heart biopsy slides (myocarditis, non-myocarditis, borderline) were reviewed by eight blinded international experts.
• Experts rendered diagnoses and provided confidence scores without clinical history.
• Inter-expert agreement and consensus were analyzed after individual review and group discussion.

Main Results:

• Full initial agreement was observed in 37 cases, with moderate consensus in 35 cases.
• Consensus was reached on 90% of cases after discussion.
• Diagnostic confidence was highest for myocarditis, lowest for borderline cases, with significant differences across categories (P < 10^-50).

Conclusions:

• Histopathological diagnosis of myocarditis, especially with subtle inflammation, is challenging for experts.
• Borderline cases present significant difficulties in achieving diagnostic consensus.
• Improved, more granular criteria, clear immunohistochemistry integration, and refined nomenclature are needed for consistent myocarditis diagnosis.