A 9-year-old girl from rural Maharashtra presents with a 3-week history of polyarthralgia affecting her knees, ankles, and wrists. Her mother reports a sore throat 4 weeks ago that resolved without treatment. On examination, she has a new systolic murmur at the apex, best heard in the left lateral decubitus position. Her ESR is 68 mm/h and CRP is 4.2 mg/dL. Echocardiography shows anterior mitral leaflet thickening with restricted motion and mild mitral regurgitation. What is the most likely diagnosis?

Explanation

## Diagnosis: Acute Rheumatic Fever with Carditis ### Clinical Presentation This child meets the **revised Jones criteria (2015)** for acute rheumatic fever (ARF) in a high-risk population (endemic region): - **Major criteria present:** 1. **Carditis** — new apical systolic murmur (mitral regurgitation) + echocardiographic evidence of valvulitis (anterior leaflet thickening, restricted motion) 2. **Polyarthralgia** — affecting multiple large joints (knees, ankles, wrists) - **Minor criteria present:** - Elevated acute phase reactants (ESR 68 mm/h, CRP 4.2 mg/dL) - **Preceding streptococcal infection:** - Recent pharyngitis 4 weeks prior ### Key Point: **In high-risk populations (endemic areas like India), polyarthralgia + carditis = ARF until proven otherwise.** The combination of carditis (clinical + echo) with polyarthralgia and recent streptococcal infection is pathognomonic. ### Echocardiographic Findings The **anterior mitral leaflet thickening with restricted motion** is characteristic of acute mitral valvulitis. The presence of mitral regurgitation on echo confirms **carditis** as a major criterion. ### High-Yield: **Revised Jones Criteria (2015) for ARF in high-risk populations:** - ≥2 major criteria OR ≥1 major + ≥2 minor criteria - **Major:** carditis, polyarthritis/monoarthritis/polyarthralgia, chorea, erythema marginatum, subcutaneous nodules - **Minor:** fever, polyarthralgia, ESR ≥60 mm/h, CRP ≥3.0 mg/dL, leukocytosis - **Plus:** evidence of preceding streptococcal infection (throat culture, rapid strep test, elevated ASO titre, or recent scarlet fever) ### Pathophysiology Group A Streptococcus (GAS) pharyngitis triggers molecular mimicry; streptococcal M protein cross-reacts with cardiac myosin, tropomyosin, and other myocardial antigens, initiating autoimmune valvulitis. ### Management Implications - **Anti-inflammatory:** High-dose aspirin (80–100 mg/kg/day) for carditis - **Eradication:** Benzathine penicillin G 1.2 million units IM (single dose) to clear any residual GAS - **Secondary prophylaxis:** Long-term penicillin (benzathine penicillin G 1.2 MU IM every 3–4 weeks OR oral penicillin V 250 mg BD) for ≥5 years or until age 21 (whichever is longer), longer if carditis present [cite:Park 26e Ch 3]