Bacterial Myocarditis
The most serious complication after untreated group A strep pharyngeal infection = myocarditis (associated with Rheumatic fever); valvular dysfunction -> acute MR -> later MS
Myocardial biopys shows interstitial fibrosis with central lymphocytes and macrophages as well as scattered multinucleated giant cells. This interstitial myocardial granuloma, or Aschoff body is pathognomonic.
Plump macrophages with abundant cytoplasm and central, slender chromatin ribbons called Antischkow (or caterpillar) cells are also often present.
Over subsequent years, Aschoff bodies are replaced by fibrous scar tissue, leading to chronic mitral valve stenosis and regurgitation.
Hypersensitivity Myocarditis, which results from an autoimmune reaction to a medication, is characterized by an interstitial infiltrate of eosinophils.
Many classes of drugs, including diuretics (eg, furosemide, HCTZ) and antibiotics (eg, ampicillin, azithromycin), can cause this hypersensitivity.
Myocarditis 2° Trypanosoma cruzi, Chagas disease -> distension of individual myofibers with intracellular trypanosomes.
Viral myocarditis -> lymphocytic interstitial infiltrate with focal necrosis of myocytes.
The younger the age, the severe the presentation of myocarditis
Infants -> acute, fulminant
Children -> acute, less fulminant
Older -> asymptomatic, precursor to dilated cardiomyopathy