Pharyngitis is one of the most common infection of the throat, we all experience this at least once in our lifetime but little do we ever think of the complication of rheumatic fever that might come along with it rarely. Rheumatic fever occurs in just 1 – 3% of the cases of pharyngitis caused by Group A streptococcus ( S. pyogenes).
This article will be focussing on the pathogenesis of rheumatic fever and the cardiac complications of it, without any further ado let’s jump in to the cause of rheumatic fever.
Pathogenesis of acute rheumatic fever:
Group A streptococcus ( S. pyogenes ) is one of the most common cause of pharyngitis is children. In the initial stage of the infection the patient experiences sore throat and a mild fever. In most of the cases the infection is cleared and the child never experiences any complications, but rarely in 1 to 3 % of the cases, after a characteristic 2 – 3 week gap the patient experiences what is known as acute rheumatic fever.
Acute rheumatic fever is caused by the cross reaction of M protein present in the bacteria with the cardiac tissue, joints and the central nervous system. Antibodies generated by the immune system against the M proteins damages the cardiac tissues, joints and CNS by compliment mediated destruction and Fc receptor bearing cells like macrophages and neutrophils. CD4 +ve cells also play a key role in initiating inflammatory responses.
Let’s see how the heart is affected by the M protein of the streptococcus:
• The antibodies against the M proteins bind to the endothelial cells of the heart and causes activation and expression of VCAM 1 adhesion molecules.
• This leads to attachment of lymphocytes to the adhesion molecules and causes lysis of the endothelium by complement mediated destruction. Lysis of endothelium exposes the underlying keratin, tropomyosin and laminin of the myocardium.
• T cells attack these underlying tissue and damages the myocardium
The inflammatory processes and other immune reaction can cause damage to any layer of the heart i.e endocardium, myocardium and pericardium.
• The involvement of pericardium results in fibrinogen exudate which is self limiting and resolves spontaneously.
• Myocardium when involved will cause myocarditis
• Valvular involvement leads to fibrinoid necrosis and fibrosis of the valve (most commonly the mitral valve is involved). This gives rise to small vegetations on the valve leaflets called as verrucae.
The same way the antibodies affect the joints causing arthritis and arthralgia. CNS tissue if affected leads to syndenham chorea which is characterised by involuntary random and rapid movements of body parts.
Arthritis:
There is migratory arthritis is in the large joints like the knee and the ankle joints most commonly. There is redness and swelling over the joint, synovial aspirate shows high leucocyte count in the synovial fluid. Resolves after 2 to 4 weeks without any disability
Syndenham chorea:
This is usually difficult to identify in children initially. Initially it makes the child less attentive, irritable, fidgety and sometimes disturbed severely. With time it progresses to uncoordinated movements seen as clumsiness and failure to hold objects properly and tendency to drop objects down. Later on frank symptoms of random, rapid and involuntary movements are seen. This also resolves without any residual neurological deficits.
Clinically on examination:
• Tongue looks like bag of worms when protruded and speech is jerky.
• Handwriting is illegible.
• Pronator sign positive – when patient is asked to raise their hand above their head, one or both hands are pronated.
• Patient fails to sustain a contraction, seen when asked to squeeze the examiner’s finger, the squeeze is irregular and intermittent gaining it’s name of milkmaid’s grip.
Let’s see what this looks like under the microscope:
There is a collection of T cells (lymphocytes), plasma cells and a characteristic macrophage called the ANITSCHKOW CELL seen, this finding is called as ASCHOFF BODIES, they are pathognomic for rheumatic fever.
ANITSCHKOW CELL – Macrophage with large pink cytoplasm and a ribbon like chromatin in the nuclei hence giving it the famous name of Caterpillar cell
Rheumatic Heart Disease:
Chronic symptoms only show a few years after the primary infection. This mainly comes with valvular dysfunction (commonly the mitral valve) leading to mitral stenosis, mitral regurgitation and arrhythmia. This is called as rheumatic heart disease.
The valve leaflet undergoes thickening and there is fusion of the valve’s commisure leading to a fish mouth appearance. All this leads to mitral valve stenosis predominantly which causes pressure overload in the atrium leading to atrial dilation. Dilation of the atrium becomes the ground for mural thrombus formation (increases risk for embolism in the systemic circulation) and arrhythmia.
The cordae tendineae may undergo thickening and sometimes even rupture leading to the prolapse of valve leaflet causing severe regurgitation.
This will be dealt in depth in another post later on about valvular heart diseases stay tuned.
Now that we have a clear idea about the pathogenesis of rheumatic fever let’s discuss on how rheumatic fever is diagnosed.
Diagnosis of acute rheumatic fever:
The diagnosis of acute rheumatic fever is based on the revised jones criteria.
Laboratory diagnosis:
1. Anti Streptolysin O titre: commonly elevated in more than 85% of cases of RF. Often other antibodies are also detected along with ASO antibody like anti DNAse, anti hyaluronidase etc.
2. Throat swab culture: This is done for identifying the bacteria in the throat swab.
3. Rapid antigen test
4. Electrocardiogram : increased PR Interval is seen, this is one of the minor manifestation of revised jones criteria.
5. Echocardiography:
This forms one of the most important tests to recognise cardiac manifestations of rheumatic fever.
Here’s a table to summarise the echocardiography findings from API textbook of medicine:
Now that we know about the pathogenesis and diagnosis of rheumatic fever, lets see the treatment aspect of acute rheumatic fever.
Treatment of acute rheumatic fever
Here’s a simple flow chart showing the algorithm of treatment in cases of acute rheumatic fever:
Antibiotics:
The precipitating group A streptococcus must be cleared first in order to control the infection and prevent relapse.
• Single dose of benzathine Penicillin 1.2 million units can be given IM. (OR)
• Amoxicillin PO 50mg/kg daily for 10 days. (OR)
• Erythromycin 250mg PO QID for 10 days.
NSAIDs and Steriods:
These play a key role in the treatment of arthritis, arthralgia and fever. There is no evidence of their role in carditis and chorea.
• Aspirin 50 – 60 mg/kg per day in 4 to 5 divided doses.
• Prednisone 1 – 2mg/kg for few days maximum upto 3 weeks for carditis only after weighing the risk and benefits of it.
Chorea:
The chorea present here is self limiting and needs no medications. But in case need arises carbamazepine or sodium valproate can be given.
The patient is advised bed rest till symptoms get better.
I hope you found this article interesting, stay tuned for more interesting content ahead.
0 Comments