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Causes of myocarditis

Created by Raja Narayan.

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Video transcript

- When we talk about what causes myocarditis, the inflammation of our heart muscle, so myocarditis or pericarditis, inflammation of the outside lining of our heart, we can think about two main causes, or etiologies. It can be either an infectious cause, meaning a micororganism like a bacterium or a virus or a fungus or something like that, or it could be non-infectious. From here we'll make some other distinctions about what we mean when we say non-infectious that's not as obvious as what I'm putting here. So it's either infectious or non-infectious and I'll talk about the main causes that fall under each of these categories. We're start up here with myocarditis, and in fact, the number one, or the most common cause of myocarditis in the First World, or the developed world, is a virus. if you want to know the detail, this virus is specifically called the Coxsackie virus or sometimes it's called Coxsackieviridae. The Coxsackie virus is the most common cause of myocarditis in First World countries and, for some reason, medical professionals like to make the distinction about the most common cause in South America, because it's an interesting pathogen, an interesting microorganism. So let's say, for instance, you just came back from watching a couple of soccer games in Brazil, maybe, and you've got this persistent chest pain, and we do a couple of tests and we realize that there is an abnormal rhythm in your heart. So over time, you find that this person is infected with a protozoan, a different class of microorganism, from a virus, and in fact Malaria is a type of protozoan, but it's not the one I'm talking about here. The specific protozoan that is involved with myocarditis from South America is known as Trypanosoma cruzi Maybe you know it better by its disease name, Chagas Disease. Chagas Disease does not only involve myocarditis, but you also get an infection of the esophagus and other parts of your body, so it's this constellation of signs that would lead physicians to start thinking maybe it's Chagas Disease instead of a typical viral myocarditis that we commonly see in the United States. Then a final infectious cause of myocarditis I should mention here, an important cause of myocarditis, is a type of bacterium. The specific genus and species of this bacterium is called borrelia burgdorferi, Which you may more readily recognize as the disease, Lyme Disease. Especially if you're from Lyme Connecticut, where it was first described. So Lyme disease is also something that can lead to myocarditis, but, mind you, this is advanced Lyme Disease. Early on, you'd get more of the skin signs that are classically associated with that and some arthritis. But myocarditis can eventually occur if you have what's called Chronic Lyme Disease. So, let's skip on down here to our non-infectious causes. The first one I want to mention for myocarditis is idiopathic. What does that mean, exactly? The way I remember it is that an idiopathic cause is one that makes us feel like idiots, because we can't actually figure out what it is. So idiopathic means, the cause of a disease that is unknown. So I'll write in parentheses, question mark. Idiopathic myocarditis is myocarditis of an unknown origin. But, because a virus is so overwhelmingly the likely cause, of myocarditis, some physicians with just chalk up idiopathic myocarditis to be likely viral in origin. So it's likely a viral myocarditis. In fact, some literature suggests that about 50% of all myocarditis is idiopathic and that, most likely, just is viral. Let's move on to our next cause right here, and this is a disorder, an immune system disorder that's called Rheumatic Fever. Rheumatic Fever is caused by a streptococcal infection. So, I'll write a Strep infection, this could be something like strep throat or it could be streptococcemia, which just means a blood infection of streptococcus throughout your blood stream. So this strep infection will then end up causing the immune system to make antibodies. And I'll abbreviate antibodies as Ab. Antibodies that attack your myocardium. So, rheumatic fever is a big deal because if it's not caught, it could potential be a life-threatening disorder that attacks the heart muscle. And this, actually, is something we're more concerned with in developing countries where we don't always treat a sore throat strep infection. In the States, if you have a sore throat that lasts long enough, people are more likely to go to the doctor and get an antibiotic for that. So other than that, there are also a couple of drugs or substances that you can take that are what's called cardiotoxic, and as the term suggests, they are no good for the heart. There are a bunch of things that are cardiotoxic such as cocaine, which is no good for any part of the body. If you abuse alcohol, if you take in too much alcohol, in a short period of time over years and years of consumption, that can be cardiotoxic. There's also carbon monoxide poisoning, which is something to be concerned about if you fall asleep in a garage with a car on. Carbon monoxide poisoning can lead to myocarditis. Certain chemo drugs that were used more commonly in the past can also cause myocarditis, and I'll give you an example of one of them called Doxorubicin. Doxorubicin is known to be associated with myocarditis in some people, but not all the time. So these are just some of the drugs or substances that you can take that can be myocardiotoxic if you want to be that specific. Finally there are also some systemic diseases that can target the myocardium to cause inflammation there. These include things like Lupus, which is a disorder where you make a bunch of antibodies against parts of your body that should not be attacked by the immune system, but are. So that can cause myocarditis. There's another disorder called Sarcoidosis, where you have granulation tissue, or inflammation tissue. Granulation tissue setting down in the myocardium causing inflammation there. There's another disorder called Systemic Sclerosis, or Scleroderma, which is when you have the connective tissue protein, collagen, being made in tissues that it shouldn't be made that commonly. So, sometimes you'll see an excess amount of collagen be made in the skin, making your skin very tight. Sometimes it's made around the esophagus, making it difficult to swallow. And scleroderma can also deposit a bunch of collagen in your myocardium to cause myocarditis as well.