Rheumatic fever develops following an immunological reaction to a recent (2-4 weeks ago) Streptococcus pyogenes infection.

Pathogenesis

• Streptococcus pyogenes infection → activation of the innate immune system leading to antigen presentation to T cells
• B and T cells produce IgG and IgM antibodies and CD4+ T cells are activated
• there is then a cross-reactive immune response (a form of type II hypersensitivity) thought to be mediated by molecular mimicry
• the cell wall of Streptococcus pyogenes includes M protein, a virulence factor that is highly antigenic. It is thought that the antibodies against M protein cross-react with myosin and the smooth muscle of arteries
• this response leads to the clinical features of rheumatic fever
• Aschoff bodies describes the granulomatous nodules found in rheumatic heart fever

Diagnostic criteria

Diagnosis is based on evidence of recent streptococcal infection accompanied by:

• 2 major criteria
• 1 major with 2 minor criteria

Evidence of recent streptococcal infection

• raised or rising streptococci antibodies,
• positive throat swab
• positive rapid group A streptococcal antigen test

Major criteria

• erythema marginatum
• Sydenham's chorea: this is often a late feature
• polyarthritis