Diagnosing lymphocytic myocarditis in adult autopsies combining the Dallas criteria with immunohistochemical stainings

Aim: Endomyocardial biopsies form the golden standard in diagnosing (borderline) lymphocytic myocarditis ((B)LM) in living patients. Herein immunohistochemistry (IH) is mandatory. Diagnosing (B)-LM in autopsy hearts however is less defined. In this study we performed immunohistochemical stainings of heart slides in a cohort of consecutive adult autopsies that were evaluated subsequently with the Dallas criteria. Methods: Sections of the myocardium of consecutive adult autopsies (n=107) performed at Symbiant, Pathology Expert Centre, from January 1, 2012, to December 31, 2012 were revised. The two Hematoxylin/Eosin (H&E) slides of the heart with the highest number of interstitial inflammatory cells were stained for LCA (leukocyte common antigen) and activated complement (C3d). The slides were then analysed for clusters (≥1) of LCA-positive lymphocytes, with or without cardiomyocyte adhesion. C3d staining was used to visualize myocytolysis. Results: In H&E slides only, LM was found in 2 out of 107 cases (1.9%), but no B-LM was diagnosed. Using IH and applying the Dallas criteria, LM was found in 4 cases (3.7%) and B-LM in 4 additional cases (3.7%) out of 107. Conclusions: Combining the Dallas criteria with immunohistochemical stainings, LCA (identifying lymphocytes) and C3d (visualizing myocytolysis), improves the diagnosis of (B)-LM in autopsy hearts.