A 35-year-old man from North India presents with a 2-week history of fever, polyarthritis (knees, ankles, wrists), and a transient pink rash on the trunk. He reports a sore throat 3 weeks ago. On cardiac examination, he has a new pansystolic murmur at the apex, an S3 gallop, and signs of acute heart failure (elevated JVP, hepatomegaly, bilateral ankle edema). Echocardiography shows mitral regurgitation with a dilated left ventricle and reduced ejection fraction (EF 35%). Blood cultures are negative. ESR is elevated at 65 mm/hr. What is the primary pathological process occurring in the myocardium?

Explanation

## Pathology of Acute Rheumatic Carditis: Aschoff Bodies ### Clinical Context: Acute Rheumatic Fever (ARF) This patient meets the **revised Jones criteria (2015)** for acute rheumatic fever: **Major Criteria Present:** - Carditis (new pansystolic murmur, S3 gallop, heart failure) - Polyarthritis (knees, ankles, wrists) - Erythema marginatum (transient pink rash on trunk) **Supporting Evidence:** - Recent streptococcal pharyngitis (3 weeks prior) - Elevated ESR (acute phase reactant) - Negative blood cultures (excludes bacterial endocarditis) ### The Aschoff Body: Pathognomonic Lesion of Acute Rheumatic Carditis **Key Point:** The **Aschoff body** is the pathognomonic histological lesion of acute rheumatic carditis. It is a granulomatous lesion unique to rheumatic heart disease. ### Microscopic Features of Aschoff Bodies | Feature | Description | |---------|-------------| | **Location** | Myocardium (perivascular connective tissue and interstitium) | | **Central component** | Fibrinoid necrosis surrounded by inflammatory cells | | **Anitschkow cells** | Activated macrophages with characteristic wavy ribbon-like chromatin ("caterpillar" or "owl-eye" appearance) | | **Aschoff giant cells** | Multinucleated giant cells formed by fusion of Anitschkow cells (NOT true epithelioid giant cells) | | **Surrounding inflammation** | Lymphocytes, plasma cells, and fibroblasts | | **Evolution** | Acute (with fibrinoid necrosis) → Healing (fibrosis and scarring) | **Mnemonic for Aschoff body components — FLAN:** - **F**ibrinoid necrosis (central) - **L**ymphocytes (surrounding) - **A**nitschkow cells (activated macrophages) - **N**on-caseating granuloma (granulomatous inflammation, but NOT caseating like TB) ### Pancarditis: All Three Layers Affected Acute rheumatic carditis is a **pancarditis** — inflammation of all three cardiac layers: ```mermaid flowchart TD A[Acute Rheumatic Carditis]:::outcome --> B[Pancarditis] B --> C[Endocarditis]:::action B --> D[Myocarditis]:::action B --> E[Pericarditis]:::action C --> C1[Valve inflammation<br/>Mitral > Aortic] D --> D1[Aschoff bodies<br/>Myocardial necrosis] E --> E1[Fibrinous pericarditis<br/>Pericardial effusion] D1 --> F[Acute heart failure<br/>Dilated LV, reduced EF]:::urgent C1 --> G[Valve regurgitation<br/>Stenosis develops later]:::outcome ``` ### Why Aschoff Bodies Form: Pathogenesis 1. **Molecular mimicry:** Streptococcal M protein shares epitopes with myosin, tropomyosin, and keratin 2. **Autoimmune response:** Cross-reactive T cells and antibodies target cardiac myosin and other myocardial antigens 3. **Complement activation:** Immune complex deposition in myocardium 4. **Inflammatory cascade:** TNF-α, IL-6, and other cytokines drive granulomatous inflammation 5. **Result:** Aschoff bodies form in the myocardium; chronic inflammation leads to fibrosis and valve scarring ### Clinical Manifestations in This Patient **Acute Carditis (This Patient):** - **Mitral regurgitation** (endocarditis affecting mitral valve) - **Dilated left ventricle with reduced EF** (myocarditis causing ventricular dysfunction) - **S3 gallop and heart failure** (consequence of myocardial inflammation and ventricular dilation) - **Pericardial involvement** (may cause friction rub, pericardial effusion) **High-Yield:** In acute ARF carditis, **mitral regurgitation** is the most common valvular lesion because the mitral valve is most frequently affected. Stenosis develops later (chronic phase) due to fibrosis and calcification. ### Evolution of Rheumatic Heart Disease | Phase | Pathology | Clinical Features | |-------|-----------|-------------------| | **Acute (ARF)** | Aschoff bodies, fibrinoid necrosis, acute inflammation | Carditis, regurgitation, heart failure | | **Healing (Weeks to months)** | Aschoff bodies resolve, fibrosis begins | Inflammation subsides; valve damage persists | | **Chronic (Years to decades)** | Valve fibrosis, thickening, calcification, stenosis | Mitral stenosis, aortic stenosis, atrial fibrillation | **Clinical Pearl:** The presence of **Aschoff bodies on myocardial biopsy** is diagnostic of acute rheumatic carditis, but biopsy is rarely performed clinically. Diagnosis is made on clinical grounds using Jones criteria and echocardiography.