Myocarditis Lecture Notes 2024 PDF

Myocarditis Dr Adam Botha Division of Anatomical Pathology University of the Witwatersrand / National Health Laboratory Service Learning objectives 1. By the end of the session the student will be able to define the terminology ass...

Myocarditis Dr Adam Botha Division of Anatomical Pathology University of the Witwatersrand / National Health Laboratory Service Learning objectives 1. By the end of the session the student will be able to define the terminology associated with myocarditis 2. By the end of the session the student will be able to list causes of myocarditis 3. By the end of the session the student will be able to describe the pathological features of myocarditis, and briefly describe the pathogenesis of myocarditis 4. By the end of the session the student will have an understanding of some of the limitations in diagnosing myocarditis Terminology Myocardial inflammation: acute or chronic inflammatory cells within the myocardium – can be primary or secondary (e.g. in cases of myocardial infarction) Myocarditis: primary inflammatory process causing myocardial injury Myocarditis Definition: diverse group of pathological entities in which infectious microorganisms and / or a primary inflammatory process cause myocardial injury Inflammatory process is the cause, rather than the response to, myocardial damage Causes of myocarditis Infectious Non-infectious Immune-mediated Idiopathic Infectious causes Viruses Bacteria Parasites (protozoa, helminths) Fungi Chlamydia Rickettsia Viral myocarditis Most common form of infectious myocarditis, and myocarditis in general Common causative viruses: coxsackie, enterovirus, influenza, Covid-19, cytomegalovirus, HIV Pathogenesis – different mechanisms possible: Direct injury to myocytes (virus detectable in myocardium) Destructive immune response Cytokine reaction may cause disproportionate dysfunction when compared to actual myocardial damage AIDS-associated myocarditis Inflammation and myocyte damage in one of three scenarios: Without a clear aetiologic agent Myocarditis attributable directly to HIV Opportunistic pathogen Other infectious causes Bacteria Corynebactrium diphtheriae - myocarditis is effect of diphtheria toxin released by organism Borrelia burgdorferi - causative organism of Lyme disease, myocardial involvement in 5% - self-limited conduction disorder Rickettsia typhi, typhus fever Chlamydophyla psittaci, chlamydia Other infectious causes - parasites Protozoan Trypanosoma cruzi: Causes Chagas disease Endemic in regions of South America 10% die during acute attack Others develop chronic immune-mediated myocarditis – may progress to cardiac insufficiency over 10-20 years Trichinosis (Trichinella spiralis) most common helminthic disease associated with myocarditis Toxoplasmosis may be associated with myocarditis in some cases Causes of myocarditis Infectious Non-infectious Immune-mediated Idiopathic Non-infectious causes of myocarditis Immune-mediated (also called hypersensitivity myocarditis) Postviral Poststreptococcal (rheumatic fever) Systemic lupus erythematosus Drug hypersensitivity Transplant rejection Non-infectious causes of myocarditis Uncertain aetiology Giant cell myocarditis Sarcoidosis Pathological findings in myocarditis Macroscopic Advanced stages – flabby myocardium Mottled appearance – pale areas and small foci of haemorrhage Mural thrombi may be present (as a complication of impaired motility of the myocardium) Late complication – dilated cardiomyopathy, and may show some degree of hypertrophy Pathological findings in myocarditis Microscopic Acute Interstitial inflammation – type dependent on cause Myocyte necrosis Chronic Resolution Healing with fibrosis Pathological findings in myocarditis Type of inflammation Viral myocarditis (and other forms of infectious myocarditis) → lymphocytes Immune-mediated → mixed inflammation, prominent eosinophils Robbins and Cotran Pathologic Basis of Disease, 9th Ed. Mitchell RN, Kumar, V et al. Eds. Elsevier Saunders, Philadelphia, 2017 Pathological findings in myocarditis – specific features / entities Giant cell myocarditis: Widespread inflammatory cellular infiltrate containing multinucleate giant cells interspersed with lymphocytes, eosinophils, plasma cells and macrophages Frequently extensive necrosis Likely represents the fulminant end of the myocarditis spectrum Carries a poor prognosis Robbins and Cotran Pathologic Basis of Disease, 9th Ed. Mitchell RN, Kumar, V et al. Eds. Elsevier Saunders, Philadelphia, 2017 Pathological findings in myocarditis – specific features / entities Chagas disease Parasitization of scattered myofibers by trypanosomes Mixed inflammatory infiltrate Robbins and Cotran Pathologic Basis of Disease, 9th Ed. Mitchell RN, Kumar, V et al. Eds. Elsevier Saunders, Philadelphia, 2017 Clinical features and complications Broad clinical spectrum May be asymptomatic – complete recovery with no sequelae Other extreme - acute onset with arrhythmia (including tachycardia) and heart failure – may lead to sudden death Fatigue, dyspnoea, fever, chest discomfort may occur Symptoms can mimic myocardial infarction (heart attack) Diagnosis High index of clinical suspicion important Can perform endomyocardial biopsy – which can be diagnostic, however, false negatives common as inflammation of myocardium may be focal or patchy Revision of main points Myocarditis refers to a specific group of conditions where the inflammatory process is the cause, rather than the response to, myocardial damage Various causes and mechanisms of myocardial damage – most commonly infectious – viral infection most important Awareness of immune-mediated causes to allow accurate diagnosis and treatment (may be part of a systemic condition) High index of clinical suspicion needed to diagnosis Thank you