Acute Rheumatic Fever
Acute immunologically mediated, multisystem inflammatory disease that occurs a few weeks folowwing an episode of Group A Streptococcal pharyngitis (throat infection - not skin).
Most ofte occurs in children between 5 and 15 (20% do occur in middle-later life).
Consequences of rheumatic fever
Deforming fibrotic valvular disease (chronic rheumatic heart disease), characterised by valvular damage and deformity (particularly mitral stenosis) decades later, which produces permanent dysfunction.
After an attack of acute rheumatic fever, there is a chance of reactivation with subsequent pharyngeal infections with similar clinical features.
Pathogenesis of rheumatic fever
Suspected that acute rheumatic fever is a hypersensitivity reaction induced by group A streptococci. Antibodies directed against the M proteins of certain strains, cross-react with glycoprotein antigens in the heart, joints and other tissues. In addition specific CD4+ T cells also react with self proteins in the heart, producing cytokines and activate macrophages, After the initial attack there may be reactivation of the disease with subsequent pharyngeal infections. Secondary prevention for RF with abx is required.
The progressive fibrosis of the valves is due to both healing of the acute inflammatory lesions and the turbulence induced by onging valvular deformities.
Microscopic features of acute rheumatic fever
- Aschoff bodies
- Anitchkow cells
- Involvement of the endocardiuma nd left sided valved by inflammatory foci results in fibrinoid necrosis within the cusps or along the tendinous cords on which site small (1-2mm) vegetations along the lines of closure called verrucae or subendocaridla lesions known as MacCallum plaques due to perhaps regurgitant jets.
Foci of swollen eosinophilic collagen surrounded by lymphocytes (primarily T cells) and occasional Anitschkow cells.
Aschoff bodies can be found in the pericardium (bread and butter pericarditis), myocardium of endocardium - therefore, RF is a pancarditis.
Plump macrophages that surround Aschoff bodies and have an abundant cytoplasm and central round-to-oval nuclei in whcih the chromatin has a central, slender, wavy pattern - catepillary cells. Some become multinucleated.
Clinical features of acute rheumatic fever
Onset of symptoms 2-3 weeks after infection (could range 10 days - 6 weeks).
Clinical diagnosis is made based on the Jones Criteria.
Requires 2 major criteria or 1 major and 2 minor, to make the diagnosis.
- Joints: migrating polyarthritis of the large joints
- <3 Carditis
- Nodules - subcutaneous nodules
- Erythema marginatum of the skin - trunk, arms, flat rash
- Sydenham chorea (neurological disorder - involuntary purposeless rapid movements).
- Lab tests: Elevated acute phase reactants (C reactive protein (CRP) and erythrocyte sedimentation rate (ESR))
- Prolonger PR interval
- Previous RG or rheumatic heart disease
- Evidence of GAS infection: antistreptolysin O and DNAse B will become positive.
Preventing reactivation of rheumatic fever
Prophylactic abx therapy is used, according to the Heart Foundation of Australia:
- All people with ARF or RHD shoudl continue secondary prophylaxis for a minimum of 10 years after the last episode of ARF or until the age of 21 years (whichever is longer).
- Those with moderate or severe RHD should continue secondary prophylaxis up to the age of 35-40 years.
Chronic rheumatic heart disease
Orgaisation of teh acute inflammation and subsequent fibrosis of the valves over time following acute rheumatic fever.
Macroscopic appearance of chronic rheumatic heart disease
Valve leaflets become thickened, commissural fusion can occur, thickening and fusion of the tendinous cords causing permanent deformity.
Mitral valve is almost always abnormal and in 60-70% of cases the mitral valve is affected alone. As such rheumatic fever is the most frequent cause of mitral stenosis and may lead to fish mouth or button hole stenosis.
Aortic valve and mitral valve are affected in 25% of cases.
Microscopic features of chronic rheumatic heart disease
Diffuse fibrosis (replacing Aschoff bodies) and often neo-vascularisation that obliterates the normal valve architecture.