Define Acute Rheumatic Fever. Describe its pathogenesis, diagnosis, clinical features and investigations.

Definition

• Acute Rheumatic Fever is a delayed, immune-mediated, multisystem inflammatory disease that follows an untreated Group A streptococcal (gas) throat infection.
• It affects the heart, joints, brain, skin and subcutaneous tissue, and is the commonest cause of acquired heart disease in children (age 5–15 years) in developing countries.

Pathogenesis

• It follows gas pharyngitis (not skin infection) after a latent period of ~2–3 weeks.
• Molecular mimicry — antibodies against streptococcal M-protein cross-react with the body's own tissues (heart, joints, brain), causing inflammation.
• The heart shows a pancarditis with characteristic Aschoff bodies on histology.

Modified Jones Criteria (2015) for Diagnosis

Diagnosis needs evidence of a preceding gas infection plus either 2 major, OR 1 major + 2 minor criteria.

Evidence of preceding gas: raised or rising ASO / anti-DNase B titre, a positive throat culture / rapid antigen test, or recent scarlet fever.

Key Clinical Features

• Carditis — the most serious feature; a pancarditis, with the mitral valve most affected (then aortic) → new murmurs (mitral/aortic regurgitation), cardiomegaly, heart failure.
• Arthritis — migratory, asymmetric polyarthritis of large joints; dramatically responsive to aspirin.
• Sydenham chorea — involuntary, purposeless movements, emotional lability (a late feature).
• Erythema marginatum — a transient, non-itchy rash with serpiginous margins on the trunk.
• Subcutaneous nodules — painless, firm nodules over extensor surfaces (associated with severe carditis).

Investigations

• Evidence of gas — ASO titre, anti-DNase B, throat swab.
• Acute-phase reactants — raised ESR and CRP; leukocytosis.
• ECG — prolonged PR interval (first-degree heart block).
• Echocardiography — detects valvular regurgitation (including subclinical carditis) and pericardial effusion.

Management

• Eradicate the streptococcus — a single dose of IM benzathine penicillin (or a 10-day oral penicillin course); erythromycin if allergic.
• Anti-inflammatory — aspirin for arthritis/mild carditis; corticosteroids (prednisolone) for severe carditis with heart failure.
• Sydenham chorea — rest, a calm environment, and haloperidol/sodium valproate/carbamazepine if severe.
• Bed rest and treatment of heart failure as needed.

Prevention

• Primary prevention — prompt treatment of streptococcal sore throat with penicillin.
• Secondary prophylaxis — benzathine penicillin IM every 3–4 weeks to prevent recurrences; the duration depends on the presence and severity of carditis (from 5 years/up to 21 years of age, up to lifelong with valve damage).

Epidemiology

• Peak age 5–15 years; associated with poverty, overcrowding and untreated streptococcal throat infections.
• Still common in developing countries; the leading cause of acquired heart disease in the young.

Detailed Features of Arthritis & Chorea

• Arthritis — flitting/migratory, affecting large joints (knees, ankles, elbows, wrists) one after another; each joint is inflamed for a few days; it is very responsive to salicylates and leaves no deformity.
• Sydenham chorea — appears late (months after the sore throat); purposeless movements, muscular incoordination, emotional lability and 'milkmaid's grip'; may occur alone.

Differential Diagnosis

• Juvenile idiopathic arthritis, septic/reactive arthritis, and other connective-tissue diseases (for the arthritis).
• Viral myocarditis and congenital/other acquired heart disease (for the carditis).

Complications & Prognosis

• The joints, skin and brain features resolve completely, but carditis can cause permanent valve damage (RHD).
• Recurrences (each risking more valve damage) are prevented by secondary prophylaxis — hence its lifelong importance in those with carditis.

Supportive Care & Follow-up

• Bed rest during the acute phase, graded as carditis improves; treat heart failure.
• Regular follow-up to monitor for evolving valve disease and to ensure adherence to secondary prophylaxis.

Role of Echocardiography

Echocardiography detects subclinical carditis (valvular regurgitation not audible clinically), which is now accepted as a major criterion — it is essential in every suspected case.