Study of Morphological Myocarditis Pathology Spectrum in Context of Lethal Outcomes

Introduction Myocarditis is an inflammatory myocardial disease that can complicate the recovery of already existing conditions or cause a sudden cardiac death with a risk from 0.3% to 14.8% across all age groups [1]. Age and gender of the patient can have an impact on the morphological subtype of myocarditis and the likelihood of developing the specific course for this disease [2]. Aim To determine the morphological features of myocarditis pathology spectrum in context of lethal outcomes. Methods 40 cases of myocardial tissue pathology cases with clinically suspected myocarditis that were sent for morphological examination to local pathology laboratory in 2002-2023 were selected for the study. Formalin-fixed formalinembedded myocardial tissue was stained by hematoxylin-eosin method and examined by light microscopy, evaluating pattern of immune cells infiltration (borderline, focal, diffuse) and composition of predominating immune cells (lymphocytes, neutrophilic granulocytes, multinucleated giant cells). Age, gender, and disease outcome of the patient were also included in statistical analysis of selected cases. Statistical analysis, including descriptive statistics (median, interquartile range, frequency), χ2 test, and Mann-Whitney U test, was performed by applying SPSS 29.0 software (p<0.05). Results 77.5% men (n=31; median – 44, interquartile range – 19 years old (y.o.)) and 22.5% women (n=9; median – 41, interquartile range – 16 y.o.; U=155.5, p=0.61) were selected for the study. Most of myocarditis cases by pattern of immune cells infiltration were borderline (32.5%, n=13) and focal (25%, n=10). Lymphocytes were predominant immune cells in 67.5% (n=27) cases, and there was 1 case (2.5%) of predominating multinucleated giant cells. Nonlethal outcome cases of inflammatory myocardial disease were more likely to manifest with borderline myocarditis (52%, n=13, χ2=14.82, p=0.002). Similar lethal outcomes of myocarditis cases were determined comparing selected cases by men vs. women (χ2=1.615, p=0.189), age (U=128.5, p=0.1), and composition of predominating immune cells (χ2=3.022, p=0.388). Conclusions Borderline myocarditis was more likely to manifest in selected cases with non-lethal outcomes. The lethal outcomes associated directly with myocarditis were similar among men and women, different age of patients, and composition of predominating immune cells infiltrate in cardiac muscle. Considering this data, it may be hypothesized that the extent of cardiac muscle injury by immune response reactions may significantly affect the clinical course of this cardiac muscle disease.