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Voiceover: Henoch-Schonlein purpura is a small vessel vasculitis. First before, we go into detail, let's look at what causes Henoch-Schonlein purpura. Here, I'm going to draw a blood vessel wall, and again blood vessels are just like pipes, so it's like we're taking cross section down the middle of a blood vessel. So we are looking at the inside of a blood vessel here and remember antibodies are attaching to the vascular wall, which recruit white blood cells because these antibodies act like a marker, and these white blood cells cause damage to the blood vessel wall. And these antibodies can group together, and there is little proteins that they're targeting and they latch on to. And so these little proteins can be shared between the antibodies. Remember these proteins are called antigens because they generate an antibody response, and a group of these antibodies and antigens is called an immune complex. Other small vessel vasculitides is antibodies may be associated or may actually be ANCA, antineutrophilic cytoplasmic antibodies. But in Henoch-Schonlein purpura, ANCA is not found. Instead what we see, are elevated levels of IgA. IgA is a specific antibody that is found on mucosal surfaces, so for example, any part of your inside that's somewhat exposed to the outside of your body. Great example is the intestines like I'm scribbling down right here. Your gastrointestinal system goes from the mouth all the way to the anus. So the gastrointestinal tract covers the distance between the mouth and the anus. You can also see IgA in your lungs or in your respiratory tract. Remember your intestines and your respiratory tract are exposed to the outside through your mouth. So IgA is a way to prevent pathogens from trying to enter inside of your body through these mucosal or "wet" surfaces of your body. Now, I want to highlight this because Henoch-Schonlein purpura is associated with upper respiratory infections. It's believed that some sort of pathogen gets into the respiratory tract causes an infection and then causes release of these IgAs to combat the infection. However, coincidentally these pathogens that are causing an infection share similar components that kind of look like the wall of blood vessels. This similarity is called molecular mimicry, and it's believed that antibodies that are released in response to an upper respiratory infection also accidentally attach onto the blood vessel walls in Henoch-Schonlein purpura. And then you also see formation of these immune complexes as well, so this case of mistaken identity, this molecular mimicry is really the cause of the disease process. And so let's take a look at the symptoms that you see. In Henoch-Schonlein purpura as we said we have an elevated IgA, so that's actually one blood test that you can use to look for Henoch-Schonlein purpura because elevated levels of IgA are normally not found in the blood, but also you can find immune complexes, and these immune complexes formed in the blood travel down to joints and can cause joint pain known as arthralgias. This can happen in the elbows as well and the shoulders too, really anywhere there is a joint. And these IgA complexes, these immune complexes also deposit in the kidney, and so you can see some kidney damage and bloody urine which is known as hematuria. And these complexes also have an affinity to get stuck in the intestines, and so you may see bloody diarrhea, bloody stools, which are known as melena, which is dark stools or hematochezia, which is bright red blood in the stools. You can also see abdominal pain. Let me take a moment to mention that you have little kids being affected by this disease. This is the most common vasculitis that affects children, so you can see a kid with abdominal pain, just screaming in pain and having all this pain in their joints as well. Added on top of that, they have bloody urine and bloody stools. That's going to terrify parents. But one of the classic symptoms of Henoch-Schonlein purpura are skin lesions. Most commonly on the buttocks, but also commonly found on the leg as well. These skin lesions are called purpura. In fact, this is not any normal type of rash or purpura, this can be felt as palpable. Immune complexes are deposing in this area causing damage to blood vessels that are supplying the skin, which is causing the death of skin cells. This rash is known to be palpable. Palpable means you can touch it, you can kind of feel the bumps if you run your fingers over it. The reason it's palpable is because of the swelling that's occurring from the immune complex deposition. So if you see these classic symptoms in a child, it can also be a teen or even adults can be affected by it, you need to treat with steroids. Steroids inhibit the immune system from causing further damage to blood vessels. And with time, this disease should actually go away. It's a very self-limiting process. Remember it was caused by an infection of the upper respiratory system so that would be the trachea, the throat, so on and so forth. And so once you treat, this illness should go away.