Heart: Rheumatic myocarditis

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1. List the histopathological features.

Aschoff bodies: focal but widely disseminated central area of fibrinoid necrosis.

Surrounded by Anitchow cells (plump macrophages)

-          elongated, condensed chromatin with spikes

-          caterpillar appearance � Longitudinal section

-          owl�s eye appearance � Transverse section

Inflammatory cells containing lymphocytes and plasma cell.

Multinucleated Aschoff giant cells.

2. Which particular part of the heart is affected in this area?

Myocardium: Interstitial connective tissue between myocardial fibres.

Note: in rheumatic fever, it usually causes pancarditis, that is usually involves all 3 layers of the heart.

3. What is the aetiology of this condition?

Streptococcus pyogenes infection.

Immune mediated inflammatory disease involving a cross reaction between antistreptococcal Ab & tissue glycoproteins.

4. Would it be useful to do a Gram stain on the slide?

No.  It is a poststreptococcal inflammatory disease, occurring 3 to 5 after the infection.

5. Rheumatic fever causes pancarditis.  How would each component of the pancarditis affect cardiac function?

Pericardium�fibrinous and serofibrinous pericarditis, bread and butter appearance.

�usually fibrin digested with resolution of exudates in uncomplicated cases.

�complication: usually little impairment of cardiac function , however if adhesive pericarditis occurs, it leads to diastolic problems and pericarditis results.

Myocardium�myocarditis � 4 chambers dilated, mural thrombosis�complete recovery (inflammatory lesions resolution�granulomatous rheumatoid nodules � damaging

  Endocardium�endocarditis, superimposed on valve �Vegetation�Little functional disturbance from acute changes.

  If repeated damage, chronic rheumatic heart disease results, with

                   - organisation

                   - deforming fibrosis

                   - commissural fusion � stenosis

                   - cusp / leaflet thickening and retraction, shortening and thickening of chordae    tendinae leading regurgitation.

6. What feature of healing leads to chronic valvular lesions following acute rheumatic valvular endocarditis?

Fibrosis

7. Explain why chronically damaged rheumatic valves are prone to infective endocarditis?

          Damaged heart valves are distorted � roughened surface, leading to calcification and   bacterial seeding  � abnormal blood flow � turbulence � plaque formation and thrombosis

8. What is the significance of asking for history of pharyngitis and joint pain?

          One third of all pharyngitis is caused by streptococcal pyogenes, and antibodies against  this bacteria crossreacts with cardiac myocytes causing rheumatic fever. Joint pain is one of the major Jones criteria for the diagnosis of acute rheumatic heart fever, the other being polyarthritis, erythema marginatum, subcutaneous nodules.

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Copyright � Joseph Ong 2003