## Etiology of Mitral Stenosis **Key Point:** Rheumatic heart disease (RHD) is responsible for >90% of mitral stenosis cases worldwide, and remains the leading cause in India and developing nations. ### Pathophysiology of Rheumatic Mitral Stenosis Rheumatic fever → post-streptococcal autoimmune inflammation → valve fibrosis, commissural fusion, and leaflet thickening → progressive narrowing of the mitral orifice. **High-Yield:** The latency between acute rheumatic fever and clinically significant mitral stenosis is typically 10–20 years; many patients do not recall the initial episode. ### Geographic and Epidemiologic Context | Feature | Rheumatic MS | Congenital MS | Calcific MS | |---------|--------------|---------------|-------------| | **Prevalence (global)** | >90% of MS | <5% | Rare in pure form | | **Age at presentation** | 30–50 years | Childhood/adolescence | >60 years | | **Associated findings** | AF, other valve lesions | Isolated; parachute valve | Aortic stenosis common | | **Geography** | Developing countries | Sporadic, worldwide | Developed countries | **Clinical Pearl:** In India, rheumatic heart disease remains endemic due to high prevalence of streptococcal infections, limited access to penicillin prophylaxis, and delayed diagnosis. The patient's age (32 years) and rural background are classic for RHD-related mitral stenosis. ### Why Rheumatic Heart Disease Dominates 1. **Post-streptococcal autoimmunity** — molecular mimicry between streptococcal M protein and cardiac myosin triggers valve inflammation. 2. **Recurrent episodes** — multiple attacks accelerate fibrosis and stenosis progression. 3. **Secondary atrial fibrillation** — develops in ~50% of symptomatic MS patients, further worsening hemodynamics. **Mnemonic: RHD-MS (Rheumatic Heart Disease–Mitral Stenosis) = "Repeat Strep → Rheumatic → Repeat attacks → Ruined valve"** [cite:Harrison 21e Ch 297]
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