Aschoff body

**Definition:** Aschoff body = focal, perivascular inflammatory granuloma in the heart of patients with acute rheumatic fever (ARF). It is the pathognomonic histologic lesion of rheumatic carditis and may be found in any layer of the heart (pancarditis: pericardium, myocardium, endocardium).

**Histology:** - Central fibrinoid necrosis (eosinophilic collagen degeneration with immune complexes/fibrin) - Surrounded by activated macrophages (histiocytes), lymphocytes (mainly T cells), and occasional plasma cells - **Anitschkow cells** ("caterpillar cells"): activated macrophages with abundant cytoplasm and central round-to-ovoid nuclei with chromatin condensed into a slender, wavy ribbon (longitudinal section looks like a caterpillar; cross section looks like an "owl-eye") - **Aschoff giant cells:** multinucleated cells derived from fusion of macrophages - Late lesions heal by fibrosis (scar formation)

**Pathophysiology:** - Follows untreated/inadequately treated group A β-hemolytic *Streptococcus pyogenes* pharyngitis (not skin infection) ~2-4 weeks earlier - Type II hypersensitivity via **molecular mimicry**: antibodies and T cells against streptococcal M protein cross-react with cardiac myosin and other host antigens (e.g., in the heart, joints, and basal ganglia) - Not an infection of the tissue itself; cultures of the heart are negative

**Clinical significance (Jones criteria, major):** - **J**oints (migratory polyarthritis) - **♥** Carditis (pancarditis) - **N**odules (subcutaneous) - **E**rythema marginatum - **S**ydenham chorea - Minor: fever, arthralgia, elevated ESR/CRP, prolonged PR interval - Plus evidence of preceding GAS infection (elevated ASO or anti-DNase B titers, positive throat culture/rapid test)

**Cardiac consequences:** - Acute: pancarditis; fibrinous/serofibrinous pericarditis ("bread-and-butter"), myocarditis (Aschoff bodies; most common cause of death in acute phase is heart failure/arrhythmia), and verrucous endocarditis (small, firm vegetations along lines of closure of valve leaflets) - **MacCallum plaques:** subendocardial lesions in the posterior wall of the left atrium, caused by regurgitant jets - Chronic rheumatic heart disease: mitral valve most commonly affected (mitral stenosis > regurgitation; "fish-mouth" valve, thickened/fused chordae tendineae, leaflet fibrosis and commissural fusion), then aortic valve. Complications include left atrial dilation, atrial fibrillation, thromboembolism, pulmonary hypertension, and infective endocarditis risk

**Management/Prevention:** - Treat GAS pharyngitis with penicillin (or amoxicillin; macrolide if allergic) to prevent ARF - ARF: penicillin to eradicate GAS, NSAIDs/aspirin for arthritis, steroids for severe carditis, and long-term secondary prophylaxis (benzathine penicillin G IM every 3-4 weeks) with duration depending on carditis/residual valve disease

**High-yield associations/pearls:** - Aschoff body (+ Anitschkow cells) = ARF; "pathognomonic" - Early lesions are granulomatous; late lesions are fibrotic - Subcutaneous nodules also show fibrinoid necrosis surrounded by palisading histiocytes (Aschoff-like) - Mitral valve is most commonly affected; mitral stenosis is the hallmark of chronic disease - Don't confuse with: Libman-Sacks endocarditis (SLE; verrucous vegetations on both sides of the valve), infective endocarditis (large friable vegetations), and Osler nodes/Janeway lesions