Model Answer
0 min readIntroduction
Rheumatic heart disease (RHD) is a chronic inflammatory condition resulting from rheumatic fever, an autoimmune response to Group A Streptococcus (GAS) infection. It remains a significant cause of morbidity and mortality, particularly in developing countries. While the incidence of acute rheumatic fever has declined in developed nations, RHD continues to pose a substantial public health challenge globally. The disease primarily affects the heart valves, leading to stenosis and/or regurgitation, ultimately causing heart failure. Understanding the pathogenesis and histopathological features is crucial for accurate diagnosis and management.
Pathogenesis of Rheumatic Heart Disease
The pathogenesis of RHD is a complex interplay of molecular mimicry, autoimmune responses, and chronic inflammation. It unfolds in the following stages:
- Initial Infection: It begins with a pharyngeal infection with Group A Streptococcus (Streptococcus pyogenes).
- Immune Response: The body mounts an immune response against the streptococcal antigens. However, certain streptococcal antigens, particularly M proteins, share structural similarities (molecular mimicry) with proteins found in the heart, brain, and joints.
- Autoantibody Production: This molecular mimicry leads to the production of autoantibodies that cross-react with these host tissues. Anti-streptolysin O (ASO) antibodies are commonly detected, but antibodies against other streptococcal antigens, like anti-DNase B, are also important.
- Inflammation: These autoantibodies deposit in the heart valves, triggering an inflammatory response mediated by T cells and macrophages.
- Carditis: The inflammation causes carditis, affecting the pericardium, myocardium, and endocardium. The endocardium is most commonly affected, leading to valvulitis.
- Valve Damage: Repeated episodes of inflammation lead to fibrosis, scarring, and ultimately, valve thickening, stenosis, and/or regurgitation.
Histopathological Features of Rheumatic Heart Disease
The histopathological features of RHD vary depending on the stage of the disease and the valve affected. However, certain characteristic findings are consistently observed:
Macroscopic Features
- Valve Thickening: Valves become thickened and fibrotic.
- Commissural Fusion: The commissures (leaflets) of the valves fuse together, leading to stenosis.
- Chordae Tendineae Fusion: The chordae tendineae may become shortened and fused.
- Vegetations: Small, warty vegetations (verrucae) may be present on the valve leaflets, particularly in the acute phase.
Microscopic Features
- Aschoff Bodies: These are characteristic granulomatous lesions found in the myocardium. They consist of elongated, serpentine cells (Aschoff cells) surrounded by lymphocytes and macrophages.
- Anitschkow Cells: These are large, plump macrophages with abundant cytoplasm and horseshoe-shaped nuclei, often found in the myocardium and valve leaflets.
- Fibrinoid Degeneration: Fibrinoid degeneration of collagen occurs in the valve leaflets and chordae tendineae.
- Interstitial Inflammation: Chronic interstitial inflammation is present in the myocardium and valve leaflets.
- Valve Leaflet Changes: The valve leaflets show thickening, fibrosis, and neovascularization.
The mitral valve is most commonly affected (approximately 70-80% of cases), followed by the aortic valve (30-40%), tricuspid valve (10-20%), and rarely, the pulmonary valve. The severity of the histopathological changes correlates with the clinical manifestations of RHD.
| Valve | Common Histopathological Findings |
|---|---|
| Mitral Valve | Thickening of leaflets, commissural fusion, chordae tendineae shortening, fibrinoid degeneration. |
| Aortic Valve | Calcification, fibrosis, commissural fusion, leaflet thickening. |
| Tricuspid Valve | Less severe changes compared to mitral and aortic valves; thickening and fibrosis. |
Conclusion
Rheumatic heart disease is a preventable condition resulting from inadequately treated streptococcal pharyngitis. Understanding the pathogenesis, involving molecular mimicry and autoimmune responses, and recognizing the characteristic histopathological features – Aschoff bodies, Anitschkow cells, and valve leaflet changes – are essential for accurate diagnosis and appropriate management. Continued public health efforts focused on early detection and treatment of streptococcal infections, along with improved access to secondary prophylaxis, are crucial to reduce the global burden of RHD.
Answer Length
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