rheumatic fever
Rheumatic fever is an illness caused by an immunological reaction following group A streptococcal infection.
Epidemiology
Risk factors include:
- children and adolescents aged 5 to 15 years
- developing nations where antibiotic prescription is low
- poverty, overcrowding
Clinical presentation
- joint pain (which is characteristically asymmetrical and migratory) and swelling - commonest presenting feature
- Sydenham chorea: uncoordinated jerky movements of the face, feet and hands - common
- fever present in most cases
- carditis may present as:
- valvulitis producing a new murmur (most common)
- myocarditis leading to cardiac enlargement and even decompensation
- pericarditis leading to a pericardial rub and effusion
- erythema marginatum and subcutaneous nodules are much rarer.
Group A streptococcal throat infection has classically been attributed as causing bouts of rheumatic fever, although group A streptococcal skin infections have also been proposed as being able to cause disease . Symptoms appear weeks after the initial infection .
Diagnostic criteria
Modified Jones criteria
Evidence of group A beta hemolytic streptococcus infection (raised anti-Streptolysin O titer, positive throat culture, recent scarlet fever or positive Streptococcal A antibodies) and 2 major or 1 major and 2 minor criteria .
- major criteria
- minor criteria
Pathology
Rheumatic fever is a multisystem immunologically mediated inflammatory disease that occurs as a direct sequelae to infection by group A streptococcus
The key mediator of the aberrant immune response is the phenomenon of molecular mimicry. Antibodies and T-cells that react against the M cell wall protein of the group A streptococcus bacteria also target various proteins found throughout the body (e.g. cardiac myosin, skin, brain, glomerular basement membrane, striated and smooth muscles) .
The binding of these auto-reactive antibodies and cells leads to inflammation and further damage. The subsequent Th2 cell activation in the convalescence period of an acute episode triggers fibrosis that can lead to the long term complications and the development of rheumatic heart disease .
Not all group A streptococcal bacteria are capable of producing rheumatic fever, likewise not all patients with a group A streptococcus infection develop rheumatic fever, so therefore there are underlying patient susceptibility and bacterial factors that determine if rheumatic fever will occur .
Microscopic appearance
Anitschkow cells (caterpillar cells) may be seen which are macrophages with chromatin condensation that can fuse to become Aschoff bodies. Aschoff bodies are pathognomonic for rheumatic fever and are comprised of a fused group of macrophages with surrounding necrotic collagen and interstitial fibrosis .
Radiographic features
Echocardiography
Echocardiography is important for assessing the valves, cardiac function and pericardium of the heart during an episode of acute rheumatic fever and for ongoing follow up. Mitral regurgitation is most commonly seen during an attack episode followed by aortic regurgitation . Echocardiography plays an important role is diagnosing so-called "silent carditis" where an audible murmur is not heard but there are still signs of regurgitation suggesting valvulitis.
Treatment and prognosis
Intramuscular benzathine penicillin injection delivered on a monthly basis, at least 10 years following the most recent attack, provides prophylaxis against group A streptococci infection and further bouts of rheumatic fever. Adherence to monthly injections is a major issue .
Repetitive episodes of rheumatic fever increases the risk of developing rheumatic heart disease, with 60% of patients eventually doing so .
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