HEART - Rheumatic Fever and Rheumatic Heart Disease


Rheumatic fever and Rheumatic Heart Disease:

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PATHOLOGY OF ASCHOFF BODIES OR NODULE )

Rheumatic fever is an acute inflammation of the connective tissue, particularly of heart and joints due to immunological reaction.

It is seen mainly in children (5 to 15 years of age) but adults may suffer the first attack.

Etiopathogenesis:

Disease follows 1-5 weeks after pharyngeal infection by Group A beta -Hemolytic Streptococcus.

There is raised Anti-streptolysin-O titre (ASO titre) in blood.

Hence, the disease is thought to be due to cross-reaction between "Antibodies to streptococcal antigen” and “Cardiac tissue antigen” (which is similar to streptococcal antigen).

The initiating beta-hemolytic streptococcal infection of the throat, introduces the streptococcal antigens into the body and may also activate cytotoxic T-cells.

These antigens lead to the production of antibodies to various antigenic components of the streptococcus, which can cross react with certain cardiac antigens, including those from the myocyte sarcoplasma and from the glycoproteins of the valves.

This may be the mechanism for the production of the acute inflammation of the heart in acute rheumatic fever that involves all cardiac layers (endocarditis, myocarditis, and pericarditis).

This inflammation becomes apparent after a latent period of 2 to 3 weeks.

This may progress to chronic stenosis or insufficiency of the valves.

Clinically, the patients give the history of fever, sore throat followed by recovery.

After about two weeks, there is appearance of the symptoms of cardiac involvement and/ or migratory large joint polyarthritis, skin involvement (erythema marginatum) and subcutaneous nodule.

Some patients may develop Sydenham chorea, a neurologic disorder with rapid, involuntary, purposeless movement.

Repeated attacks or severe first attack causes chronic rheumatic heart disease leading to congestive cardiac failure.

Pathology:

Lesion develops in three stages:

1. Stage of exudation (edema with inflammatory cells) with fibrinoid necrosis.

2. Stage of cellular proliferation with formation of Aschoff body.

3. Stage of healing by fibrosis.

Aschoff body:

It is the characteristic lesion of the Rheumatic disease.

It consists of:

1. Cental fibrinoid necrosis ;

2. Surrounded by inflammatory cells and large, mono or multinucleated cells with transverse chromatin (Caterpillar cell or Anitschkow myocyte) ;

3. Fibroblasts encircling the above elements.

Aschoff bodies are situated on one side of the small arteries and are characteristically seen in the myocardium.

Lesions :

- Extracardiac Rheumatic Lesions:

1. Joints - Larger joints are involved. Example: knee, ankle, elbow, wrist, shoulder and hip joints.

Aschoff bodies are formed in the synovial membrane, capsule, ligament etc. with serofibrinous effusion.

2. Serous membranes with effusion.

3. Skin- Erythema marginatum.

4. Subcutaneous tissue -Rheumatic nodule mainly seen over the bony prominences. Example: mastoid, knuckle, elbow, patella, scapular margin etc.

- Cardiac Rheumatic Lesions:

Heart (Pancarditis) - involves pericardium, myocardium and endocardium (valvular and mural).

Pericardium:


Grossly, due to acute fibrinous inflammation, pericardium loses its shiny, glossy appearance and becomes rough.

Sticky fibrinous exudate binds two layers of pericardium and on separation the rough surface shows “bread & butter” appearance.

Occasionally, there is a small amount of serofibrinous exudate in the pericardial sac.

Microscopic appearance :

Loss of endothelium with deposition of inflammatory cells - lymphocytes, plasma cells and occasionally polymorphs.

An occasional subpericardial Aschoff body may be present.

Fate:

1. Complete resolution

2. Organization with:

-i) Adhesion between two layers of pericardium (Adhesive pericarditis).

-ii) Adhesive pericarditis with adhesion to mediastinal structures (Adhesive mediastino-pericarditis).

-iii) Milk spot on the anterior surface of the left ventricle.

It is an unresolved patch of rheumatic pericarditis healed by organization.

Myocardium:

Aschoff bodies the characteristic lesion of rheumatic disease, is typically seen in the loose connective tissue of the myocardium, located characteristically near a small blood vessel.

Myocardial fibers are separated by edema and infiltrated with inflammatory cells .

In acute phase of exudation, heart is enlarged with functional disorder.

Later, Aschoff bodies are formed as minute white specks under endocardium, particularly in the left side of the heart at the base of the interventricular septum.

Aschoff bodies are present in the connective tissue between the muscle fibres and cause secondary degeneration of the muscles.

Aschoff bodies are healed up by fibrosis and myocardium is riddled with scarred areas resulting in myocardial failure.

Endocardium:

1. Mural endocardium, particularly in the posterior wall of the left atrium, just above the mitral valve, become rough, thick and later on scarred (MacCallum’s patch).

This is due to subendocardial aggregation of Aschoff bodies followed by fibrosis.

2. Valvular endocardium:

Most harmful effect of rheumatic disease is due to involvement of cardiac valves.

Mitral valve is most commonly affected, mainly in women, followed by aortic valve, mainly in men.

Tricuspid valve is rarely affected.

Pulmonary valve is practically never affected.

Inflammed valve cusps become edematous, thickened and there is formation of Aschoff bodies in the subendothelial connective tissue.

Continued work of the inflamed valves causes loss of endothelium due to trauma along the line of contact (a few millimeters above the free margin of the cusps).

On this raw surface platelets and fibrin are deposited forming minute, pale thrombi called rheumatic vegetations.

In course of time vegetations are organized and covered by the growth of the adjacent endothelium.

Rheumatic Vegetations:

1. Tiny (size of a pin’s head), sessile arranged in a row and firmly fixed with the underlying tissue, hence there is no embolism.

2. These are situated in the valve cusp, a few millimeters away from the free margin (this is the most traumatized area).

3. Vegetations may be situated on the auricular surface of mitral valve and ventricular surface of the aortic valve.

4. These are organized and endothelialized pale thrombi.

Aschoff bodies are also found in the chordae tendineae, which become fibrosed and shortened.

During acute stage, inflamed edges of cusps adhere together and later become fibrosed causing narrowing or stenosis.

Repeated attack of rheumatic fever causes repeated injury to valves and chordae tendineae, which become fibrosed, thickened and shortened.

Valve cusps appear as diaphragm with a central slit called ‘button hole’ type of mitral stenosis, commonly seen in adults.

Fusion of cusps with shortening of chordae tendineae produce ‘funnel shaped’ mitral stenosis with oval orifice at the apex of the funnel.

This is commonly seen in children.