A 38-year-old man from rural India presents with fever for 3 weeks, progressive dyspnea, and a new diastolic murmur at the left sternal border. He has a history of rheumatic heart disease diagnosed 10 years ago. On examination: temperature 38.5°C, heart rate 102/min, blood pressure 140/80 mmHg, splinter hemorrhages on fingernails, and Osler nodes on fingertips. Blood cultures (before antibiotics) grow alpha-hemolytic streptococci. Transthoracic echocardiography shows a 12 mm vegetation on the aortic valve with mild aortic regurgitation. What is the most likely diagnosis according to the modified Duke criteria?

Explanation

## Modified Duke Criteria for Infective Endocarditis Diagnosis **Key Point:** The modified Duke criteria use major and minor criteria to classify IE into definite, possible, or rejected categories. This patient meets multiple major criteria. ### Major Criteria (2 points each) 1. **Blood culture positive for typical IE organism** — alpha-hemolytic streptococci (Streptococcus viridans) in 2 separate cultures or persistently positive cultures = 2 major points 2. **Echocardiographic findings** — vegetation ≥10 mm on valve = 1 major point (note: oscillating vegetation, paravalvular abscess, or new regurgitation also count as major) 3. **New regurgitation** — aortic regurgitation on echo = 1 major point ### Minor Criteria (1 point each) - Fever ≥38.5°C = 1 minor point - Vascular phenomena (splinter hemorrhages, Osler nodes) = 1 minor point - Predisposing condition (rheumatic heart disease) = 1 minor point ### Scoring - **Definite IE:** ≥2 major criteria OR 1 major + 3 minor criteria OR 5 minor criteria - **Possible IE:** 1 major + 1 minor criterion OR 3 minor criteria - **Rejected IE:** <2 major, <1 major + 3 minor, or <5 minor criteria (and alternative diagnosis explained) This patient has **3 major criteria** (positive blood culture, vegetation on echo, new aortic regurgitation) = **Definite IE**. **High-Yield:** Viridans group streptococci are the most common cause of IE in patients with underlying valvular disease (rheumatic heart disease, mitral valve prolapse). They are alpha-hemolytic on blood agar. **Clinical Pearl:** The presence of splinter hemorrhages and Osler nodes (painless nodules on fingertips) are classic stigmata of IE but are minor criteria only — they are less sensitive and specific than previously thought. **Mnemonic — ABCDEF of IE:** Aortic/Aortic regurgitation, Blood culture positive, Cardiac murmur (new), Duke criteria, Echocardiography (vegetation), Fever. ### Differential from Acute Rheumatic Fever | Feature | IE | ARF | |---------|----|-----------| | Blood culture | Positive (organism isolated) | Negative | | Vegetation location | Valve leaflet edges (endocarditis) | Verrucae on closure line (MacCallum patches) | | Murmur onset | New, often regurgitant | May be functional, often Carey Coombs | | Echocardiography | Large vegetation (>10 mm) | Leaflet thickening, no large vegetation | | Duration of fever | Weeks to months | Usually <2 weeks | [cite:Harrison 21e Ch 137]