08-19-2018, 07:15 PM
Rheumatic fever is an immunologically-mediated disease that can occur 2-4 weeks after an untreated group A β-hemolytic streptococcal pharyngitis.
Rheumatic fever is caused by an immune response mounted against streptococcal M proteins that also targets structurally similar cardiac antigens. This phenomenon is referred to as molecular mimicry.
Rheumatic fever is a type 2 hypersensitivity reaction.
The diagnosis of rheumatic fever is based on the evidence of a recent strep infection (e.g., serology such as ASO titer or anti-DNase B titer) and Jones criteria (discussed below).
Either more than 2 major Jones criteria or more than 1 major criterion and more than 2 minor Jones criteria are required for diagnosis.
Major JONES criteria include:
• Joint findings (e.g. migratory polyarthritis)
• O, which represents carditis (think of the “O” as the rough shape of the whole heart, including all three layers-endocardium, myocardium, pericardium), which may include endocarditis, myocarditis, and/or pericarditis
• Nodules (subcutaneous) on extensor surfaces (e.g. wrist, elbow, knee)
• Erythema marginatum, which is a macular rash starting on trunk/arms
• Sydenham chorea (chorea, hypotonia, emotional lability)
Minor Jones criteria include:
• Fever
• Arthralgia (however, arthralgia cannot be used as a minor criteria if polyarthritis is counted as a major criteria)
• Increased serum levels of acute phase reactants (e.g. CRP, ESR)
• Prolonged PR interval on ECG
The 5 “A findings” associated with rheumatic fever include:
• A group β-hemolytic streptococcal pharyngeal infection
• Aschoff bodies, which are sites of focal interstitial myocardial inflammation with a granuloma
• Anitschkow cells, which are activated histiocytes with a rod shaped “caterpillar” nucleus
• ASO titer elevated (anti-streptolysin O)
• Antibodies to M protein (immune mediated type II hypersensitivity)
The heart valves most commonly affected by rheumatic fever in decreasing order of frequency are:
• Mitral
• Aortic
• Tricuspid
Mnemonic: rheumatic fever: mitral more than aortic more than tricuspid
The acute valvular complication of rheumatic heart disease is mitral valve regurgitation, while the chronic valvular complication is mitral stenosis. Note that rheumatic heart disease is virtually the only cause of mitral stenosis.
The stenotic mitral valve in rheumatic heart disease has 'fish-mouth' appearance. Thickening and fusion of the chordae tendineae and cusps may also be seen.
Aortic valve involvement in rheumatic heart disease may lead to fusion of the commissures.
Important histological findings in rheumatic heart disease myocarditis include:
• Aschoff bodies, which are granulomas with giant cells.
• Anitschkow cells, which are enlarged macrophages with a ribbon-like nucleus. Anitschkow cells are also referred to as “caterpillar cells” and are pathognomonic for rheumatic heart disease.
Treatment and prophylaxis for rheumatic heart disease is penicillin.