Rheumatic fever Flashcards
Definition
Pharyngeal infection with Group A β-haemolytic Streptococcus pyogenes (”strep throat”) can result in molecular mimicry 2-4 weeks later whereby M protein antibodies cross-react with self-antigens in skin, joints, heart & brain. If the antibodies cross-react with antigens in the heart, this is rheumatic heart disease.
Only 3% of people with streptococcal pharyngitis develop rheumatic fever.
Epidemiology
NOTE: Note everyone with streptococcal pharyngitis (”strep throat”) develops rheumatic fever, only 3%.
- “Disease of the poor, typically occurs in LEDCs”- occurs due to overcrowding, uncommon in developed countries due to antibiotic use
- Children & adolescents 5-17 years
Aetiology
- Typically develops 2-4 weeks after streptococcal pharyngitis (throat infection with Group A β-haemolytic Streptococcus pyogenes)
Streptococcus pyogenes microbio indentification?
Streptococcus pyogenes = Group A β-haemolytic streptoccus
- Catalase -ve (when 3% H202 is added, no bubbling is observed as breakdown of hydrogen peroxide to H20 & O2 doesn’t occur) = streptococcus
- S.Pyogenes is β-haemolytic meaning that when cultured on blood agar it completely lyses RBCs, resulting in colourless medium. It appears as gram +ve chains of cocci.
- Lancefield group A
Pathophysiology w/ presentation
Group A β-haemolytic S. Pyogenes has a highly antigenic M protein so the immune system produces antibodies against it. These M protein antibodies cross-react with self-antigens in skin, joints, heart, brain & other tissues causing inflammation. This is known as molecular mimicry (antibody-mediated destruction of own cells because self-antigens have similiar structure to microbial antigens). This is a type 2 hypersensitivity reaction.
- In the skin: erythema marginatum (ringed rash on arms & trunk)
- In joints: athralgia (joint pain) & migratory polyarthritis of joints (multiple large joints become inflamed & painful one after the other. As 1 starts to improve, another gets worse.)
- In heart: Rheumatic heart disease. Presence of Aschoff bodies histologically (areas of fibrinoid necrosis in myocardium).
- In brain: due to autoimmune reaction in the basal ganglia (responsible for initiating movement), Sydenham chorea occurs (rapid overshooting jerky movements of face & arms). Typically occurs 3 months after initial infection.
RHEUMATIC HEART DISEASE occurs in 50% of cases of rheumatic fever due to M protein antibodies cross-reacting with self-antigens in the heart. Results in pancarditis (infective endocarditis, myocarditis, pericarditis) & damage to heart valves, mainly mitral valve. Rheumatic heart disease is the MOST COMMON cause of mitral stenosis as valve leaflets become fibrosed after inflammation (most common). Mitral regurgitation> aortic regurgitation.
Histological finding in rheumatic heart disease? Common exam Q
Presence of Aschoff bodies (areas of fibrinoid necrosis w/ immune cells in myocardium)
Signs & symptoms
Recent history of scarlet fever (rash caused by Group A β-haemolytic strep) or sore throat (streptococcal pharyngitis) 2-4 weeks before = classic presentation of rheumatic fever AND
*RHD = rheumatic heart disease
Signs
- New murmur (mitral regurgitation murmur = pansystolic murmur, mitral stenosis murmur = low-pitched rumbling mid-diastolic murmur)- RHD
- Erythema marginatum
- Subcutanous nodules
- Syndenham’s chorea
- Migratory polyarthritis
Symptoms
- Athralgia
How to demonstrate recent Strep infection (3)?
- Rapid antigen tests for group A streptococci
- Throat culture
- Serology- anti-streptolysin O titre is commonly used (streptolysin O & S are virulence factors that bind cholesterol in target membranes to form pores)
Investigations
- Throat culture or rapid antigen test for Group A streptococci- to identify recent strep infection
- ESR - raised, inflammatory marker
- CRP- raised, this is an acute phase protein which increases during inflammation.
- CXR- may show evidence of congestive heart failure , a MAJOR criterion which is a complication of untreated/chronic RHD (ABCDE: Alveolar oedema, Kerley B lines, Cardiomegaly, Dilated upper lobe vessels, Pleural effusions). May show cardiomegaly secondary to valve defect
- Echocardiogram - may show mitral regurgitation or stenosis or aortic regurgitation (RHD affects mainly the mitral valve. RHD is the MOST COMMON cause of mitral stenosis), pericardial effusion if pericarditis present
Diagnosis?
Jones criteria for diagnosis
Evidence of recent streptococcal infection + 2 major criteria OR 1 major & 2 minor criteria
Major criteria
- New murmur OR heart failure
- Arthritis (typically migratory polyarthritis which affects multiple large joint one after the other)
- Erythema marginatum (ringed rash with clear centres on trunk & arms)
- Syndenham’s chorea (rapid jerky movement of face & arms, typically occurs 3 months after initial infection)
Minor criteria
- Raised ESR & CRP
- Pyrexia
- Athralgia (joint pain)
Management
- Antibiotics: IV benzylpenicillin STAT (immediately) followed by 10 day course of phenoxymethylpencillin.
- If Syndenham’s chorea present, use Haloperidol or Diazepam (benzodiazepine).
Complications (3)
- Congestive heart failure (in chronic or untreated cases)
- Valve diseases: most commonly affected is the mitral valve, followed by the aortic valve. Rheumatic fever causes: mitral stenosis (valve cusps become fibrosed due to inflammation)> mitral regurgitation > aortic regurgitation. Rheumatic fever is the most common cause of mitral stenosis.
- Infective endocarditis- people with previous rheumatic heart disease are more likely to get IE as the cardiac endothelium is damaged or abnormal, allowing bacteria to adhere & form vegetations.
