Tag: erythema marginatum

Quick Look at Infective Endocarditis & Rheumatic Heart Disease.

People are often mislead by these two disease conditions where they are completely different from each other. I am going to talk about these two disease conditions in comparison two each other under following topics;

  1. Definition
  2. Etiology
  3. Pathogenesis
  4. Morphology
  5. Clinical aspect

Rheumatic Heart Disease (RHD) is a multi system involved, immunologically mediated followed by a group A beta haemolytic bacterial infection. It is not a direct infection on heart.

In contrast, Infective Endocarditis (IE) is a direct infection on heart valves or mural endocardium which leads to formation of large, friable vegetations containing thrombotic debris, fibrin, dead organisms and white blood cells, and live causative organisms, which would erode and destroy the surrounding tissue. This is a direct invasion of the heart.

Moving on to the etiology of Rheumatic Heart Disease (RHD), the main causative organism is a group A beta haemolytic bacteria ( mainly streptococci). Usually it is preceded by a streptococcal pharyngitis. But there are incidents where a streptococcal skin infection can also give rise to RHD. Mainly it is associated with people who are having  poor hygiene, low economic states.

Rheumatic Heart Disease (RHD) has two forms as acute RHD and chronic RHD. Both are accounted by the same organism, but the rate of disease progression, duration of disease existence and clinical features are different. Let’s talk about them under clinical aspect.

Infective Endocarditis (IE) is having two types as Acute IE and Subacute IE. Causative organisms are bit different from one to another. In acute IE, mainly a valve which was previously normal will be infected by a highly virulent organism. The most accounted causative organism is Staphylococcus aureus. Subacute IE mainly occur in people with defective valves due to one or more of following reasons;

  • A valve damaged by Rheumatic heart disease with scarring
  • Bicuspid aortic valve
  • Prosthetic valve
  • Surgery done in heart to rectify an anatomical defect in heart or in valves, acquired or congenital.
  • Degenerative calcific valvular stenosis

Subacute IE mostly occurs from less virulent organisms such as Streptococcus viridans who are normal flora of oral cavity. Predisposing conditions which would lead to this type would be dental surgeries, surgeries in gut, intravenous drug abuse, valvular abnormalities, etc. A condition which has the potential to give rise to a bacteremia or a fungemia can cause subacute IE.

Apart from above, HACEK group, fungi, virus, enterococci can infect endocardium. Even though IE is mostly occurring in left side of the heart, in groups like Intravenous drug abusers right side of the heart also can be infected.

Rheumatic Heart disease almost always affect the left side of the heart. But disease progression can deteriorate the function and anatomy right side of the heart.

Moving on to the pathology, Rheumatic Heart disease is mainly an immunologically mediated disease.What happens is, when streptococci organisms invade, body starts fighting back. Antibodies are made against mainly strptococcal M protein and hyaluronic acid. These antibodies will be mislead as these antigens can mimic self antigens in the body in places like heart, joints, etc. Not only that CD4+ T cells will get activated as a defense mechanism and they will secrete several cytokines which would ultimately activate ,macrophages which would lead the destruction. This process is augmented by neutrophil activation mediated by antibodies via classical pathway. So it is obvious that heart does not suffer a direct invasion of organisms.

Morphology of RHD is easy to remember if someone knows the pathogenesis. In acute RHD, there will be foci containing fibrin thrombotic debris, neutrophils and activated macrophages within endocardium, myocardium or pericardium which can cause “Pancarditis”. These are called Aschoff Bodies. Activated macrophages are seen as large cells with condensed and ribbon like chromatin which would be seen as a caterpillar (hence called catepillar cells) which are known as antischkow cells. Due to the inflammation in the endocardium valves and chordate tendinae will be subjected to fibrinoid necrosis. On the top of these necrotic foci, bland, non suppurative, small, warty vegetation along the margins of the closure of valves will be developed. These are called varrucae bodies. Subendocardial lesions are made worse due to the frequent damage from regurgitation jets  (initially there is a regurgitation) which would lead to irregular thickening of the endocardium called “McCallum Plaques”.Acute RHD could be having pancarditis, pericardial rub serofibrinous or fibrinous pericarditis. In chronic RHD, due to constant damage to valves and the chordate tendinae, these will be fibrotic and damaged. There will be shortening of tendinae leading to inadequate closure of the valves leading to regurgitation. Also there will be fusion of the commissures of the valves and the chordate tendinae, leading to stenosis, which would give rise to a fish mouth appearance in the mitral valve. Virtually the only reason for mitral valve stenosis is RHD.

Moving on to the pathogenesis of Infective Endocarditis (IE), basically in acute IE, as the organism is highly virulent, they can directly damage the endocardium and expose the tissue factors and vonWilbrand factors which would lead to activation of platelets. In turn plates will be aggregated on top of these leading to formation of massive, suppurative, friable masses ON THE TOP OF THE VALVES with dead cells, fibrin, and causative organism. More the platelets aggregate, more the size of the vegetation. And more the size of the vegetation, higher the number of organisms established within it. In Subacute IE, a granulation tissue can be seen at the bottom of the lesion which would indicate the features of healing. Finally if this is healed, it would be by fibrosis.

Moving on to the clinical aspect, Acute Rheumatic Heart Disease is often easily diagnosed. Main factors to establish a diagnosis would be ;

  1. Evidence of a preceding streptococcal infection
  2.  with two or more from the MAJOR CRITERIA (Migratory poly arthritis, pancarditis, subcutaneous nodules, sydenham chorea, erythema marginatum)
  3. or  with one from the MAJOR CRITERIA and two or more from MINOR CRITERIA (Fever, arthralgia, previous RHD, Acute phase reactants, prolonged PR interval)

In acute RHD, rheumatoid factor would be positive. There are conditions it is negative too. Also there will be streptolysin O or DNase B antigen circulating the blood stream, which would help in final diagnosis. But the clinical diagnosis would be critical rather than depending on the investigations.

Rheumatic heart Disease, even if it is easy to diagnose, the patient might not present to a doctor at initial stage as the disease progression may take place over many years. This is a major draw back.

Infective endocarditis is bit difficult to diagnose mainly due to 3 reasons;

  1. Prior antibiotic therapy/ Antibiotic abuse
  2. As the vegetation is large, organisms are deeply buried in the lesions, without being released into the blood stream.
  3. difficulties in isolating the organism ( eg :- many etiological agents are causing it. If a correct culture is not done, a growth cannot be expected)

Few clinical features are;

  • Splinter / subungual hemorrhages – due to micro-thrombo embolism from the friable vegetation.
  • Osler’s nodes – Subcutaneous nodules in the pulp of the digits.
  •  Janeway sign – erythematous or hemorreghic lesions on the palms and soles.
  • Roth spots – retinal hemorrhages

These are the facts which you can establish a distinct difference between these two conditions. If you know the basics, it would be easy to work them out, rather than keeping everything in memory.

 

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