What is Rheumatic fever?

- Cause: occurs after infection with Streptococcus. It need not be the Strep that produces a toxin.

- Mechanism: antibody - antigen cross reactivity. The body mounts a reaction to the Strep and it also as an innocent bystander, damages the heart, brain , skin. joints etc. in RF. These various body structures look to the immune system as does the Strep - called Molecular Mimicry.

How do you make a diagnosis of group B hemolytic strep?

Based on microbiology - Its hemolytic on a blood culture agar.

For a quick diagnosis:

Based on ab- ag complex - A quickey strep test- a Q test.

After a cotton swab test you look for the antigen of the strep - an immunologic diagnosis. Your substrate also includes the antibody and if the two are there you get a reaction.

Why the big fuss over whether a child has strep throat? - because of the possible consequence of RF:

The Jones criteria: Major manifestations of RF:

- carditis - pancarditis involving all layers of the heart

- polyarthritis

- Sydenham's chorea

- erythema marginatum

- subcutaneous nodules

Minor manifestations:

- fever

- arthralgia

- previous RF

- increased erythrocyte sedimentation rate or positive C-reactive protein.

- prolonged P-R interval

RF has a relation to the different parts of the strep wall:

- the so called M protein ( involved in the virulence on the strep) cross reacts with the sarcolemma and myosin in the human cardiac muscle.

- Cell membrane lipoproteins cross react with antigens in neurons and the caudate nucleus which is responsible for the chorea (abnormal movements) seen in a child with RF.

- Cell wall CHO react with glycoproteins in the heart valve.

Here we see the way Molecular Mimicry of the cross reacting ab - ag complexes can cause the various manifestations of RF.

The pathonamonic inflammatory lesion in the myocardium is the aschoff body. This is the localized aggregate of inflammation in the intersitium, not within the muscle cells but in the connective tissue between the muscle cells. They tend to be around blood vessels and are composed of characteristic cells, some of which may be multinucleated giant cells( the aschoff giant cells), histiocytes , and modified muscle cells. Some of the cells have elongate "caterpillar" nuclei. See figure #1.

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What does RF do?

- During the acute phase - can cause arrhymias, heart failure, and occasionally a person dies in the acute phase of left ventricular failure. Essentially RF is a pancarditis , or an immunologically mediated inflammation, involving all levels of the heart - peri, myo, and endocardiums as well as the valvular endocardium.

- The main worry is the chronic sequelae of the recurrent attacks of RF that lead to a

scarred deformed valve - most commonly the mitral valve. In the slide we know the mitral valve is being depicted because we see the smooth left atrium compared to the rough right atrium. The valve is stenotic. ** RF is the only factor that can cause mitral stenosis as opposed to the many factors that cause mitral valve insufficiency.**

Category: Pathology Notes