Rheumatic Heart Disease: Pathogenesis, Aschoff Bodies & Valvular Lesions

**1. Etiology & Pathogenesis (Molecular Mimicry)** Rheumatic Heart Disease (RHD) is the chronic fibrotic cardiac sequel of Acute Rheumatic Fever (ARF). ARF is an acute, immunologically mediated, multi-system inflammatory disease occurring 2 to 3 weeks following **Group A Streptococcal (GAS) pharyngitis** (*Streptococcus pyogenes*). * **Molecular Mimicry**: Bacterial surface **M protein** epitopes share conformational structural homology with human cardiac antigens (cardiac myosin, laminin, and vimentin). * **Immune Response**: Host humoral antibodies and CD4+ T lymphocytes cross-react with cardiac self-antigens, causing antibody-dependent cytotoxicity, microvascular damage, and immune granuloma formation across all three layers of the heart (**Pancarditis**). **2. Pathognomonic Histopathology (The Aschoff Body)** * **Aschoff Nodules**: Focal pathognomonic granulomatous inflammatory lesions situated predominantly in the myocardial interstitium and subendocardium. * **Components of an Aschoff Body**: 1. *Central Zone*: Fibrinoid necrosis consisting of necrotic collagen and deposited immunoglobulins. 2. *Anitschkow Cells (Caterpillar Cells)*: Specialized reactive histiocytes/macrophages with abundant amphophilic cytoplasm and elongated vesicular nuclei with central wavy, serrated chromatin condensation resembling a caterpillar on longitudinal section. 3. *Aschoff Giant Cells*: Multinucleated macrophages formed by coalesced Anitschkow cells. 4. *Peripheral Infiltrate*: Surrounding CD4+ T lymphocytes and plasma cells. **3. Valvular Pathology & Fish-Mouth Stenosis** * **Acute Stage**: Small, sterile, translucent, wart-like verrucae (1–2 mm) form along the lines of valvular closure, caused by fibrin deposition on inflamed endothelium. * **Chronic Valvular Deformity**: Decades of recurrent inflammation cause diffuse leaflet thickening, commissural fusion, chordae tendineae shortening and thickening ("cords of rope"), and dystrophic calcification. * **Valvular Predilection**: - **Mitral Valve Alone**: 65–70% of cases (presents characteristically as "Fish-Mouth" or "Buttonhole" Mitral Stenosis). - **Mitral + Aortic Valve**: 25% of cases. - Tricuspid and Pulmonary valves are rarely involved. * **MacCallum's Patch**: A roughened, irregular patch of subendocardial thickening in the posterior wall of the left atrium resulting from regurgitant blood jets. **4. Diagnostic Criteria & Laboratory Evaluation** * **Revised Jones Criteria (Evidence of Preceding GAS Infection + 2 Major OR 1 Major + 2 Minor)**: - *Evidence of GAS*: Elevated or rising Anti-Streptolysin O (ASO) titer (>200 IU/mL) or Anti-DNase B, or positive throat culture. - *Major Criteria (JONES)*: **J**oints (Migratory polyarthritis), **O** (Carditis / Valvulitis), **N**odules (Subcutaneous painless nodules over extensor bony prominences), **E**rythema marginatum (Serpiginous non-pruritic erythematous rash with pale center), **S**ydenham's chorea (St. Vitus dance, involuntary purposeless choreiform movements). - *Minor Criteria*: Fever, arthralgia, elevated ESR / CRP, prolonged PR interval on ECG. **5. 📖 Standard Textbook Reference** * *Robbins and Cotran Pathologic Basis of Disease*, 10th Ed., Ch. 12: Heart, pp. 560–566. * *Harrison's Principles of Internal Medicine*, 21st Ed., Ch. 352: Rheumatic Fever, pp. 2680–2685.