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Health and medicine
Course: Health and medicine > Unit 3
Lesson 15: VasculitisPolyarteritis nodosa
Polyarteritis nodosa is a type of vasculitis that affects small to medium arteries and leads to significant narrowing of the vasculature. Patients with polyarteritis nodosa can have symptoms like bloody diarrhea, skin lesions, and impaired motor function caused by neuropathy. Learn how health care professionals diagnose and treat polyarteritis nodosa by examining arteriograms and prescribing steroids. Created by Ian Mannarino.
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- why is the immune system not destroying the malfunctioning white blood cells(2 votes)
- The WBCs are not malfunctioning. The antibodies are attaching to self-proteins that look identical to nonself proteins. The WBCs will attack what the antibodies tell them to attack.(2 votes)
Video transcript
- Polyarteritis nodosa. This is a medium vessel vasculitis that affects many arteries. And so, if we break it down,
we can see poly means many, arter refers to the arteries,
and itis is inflammation, just like any vasculitis
you see some inflammation, and nodosa means nodular. So, when you break this
name down, we see that many arteries have
inflammation and are nodular. So, why is it nodular? Well, to understand that,
let's draw out a blood vessel. Remember that blood
vessels are like pipes. They carry blood and distribute
nutrients throughout the body. And so, here I'm shading in
the wall of the blood vessel, and in the back, I'm kind of drawing this little circular appearance. I'm trying to show you it's
a little bit of a 3D drawing. So, imagine you take a cross section through the blood vessel,
right down the middle. So, you can see that blood and nutrients would travel down this blood vessel. So, remember with vasculitis the body is mistaking the blood vessels to be a foreign protein
or something foreign, and so antibodies,
little Y-shaped proteins that are released by the immune system, are targeting the blood vessel wall, because they think it's foreign. Remember, antibodies act
as markers to draw in white blood cells to cause
some damage to the area, because these white blood
cells release molecules that are very destructive. The intent is to kill pathogens, but here you're accidentally
killing the blood vessels. And so, one theory as
to why the antibodies are accidentally targeting blood vessels is the theory of molecular
mimicry, molecular mimicry. What is molecular mimicry? Well, it's the theory
that foreign proteins, such as bacteria, viruses,
or really anything bad, any pathogen that gets in your body, are recognized by the immune system. The immune system, of course,
creates these antibodies to target these bad foreign proteins. And so, this is good. This is what antibodies are used for. They're supposed to
target foreign proteins, to mark them for destruction
for white blood cells, but in the process of recognizing
these foreign proteins, many antibodies are created. So now the immune system is ramping up to find and seek out
these foreign proteins if they ever appear again. Now the idea of molecular mimicry is that there are self proteins, such as maybe proteins from
the blood vessel walls, that look identical to foreign proteins. Now, I know I've drawn them
as little circles here, but let's say that they're identical, and these antibodies that were created in response to these foreign proteins now also are recognizing self proteins, because the self looks very similar to these foreign proteins. This is the core of molecular mimicry. In polyarteritis nodosa, hepatitis B is actually found in about
20 to 30% of patients, so it's believed that maybe hepatitis B, the proteins that are in this virus, can cause a molecular mimicry and look very identical to self, and so these foreign hepatitis B molecules look like self and induce this entire autoimmune destruction of blood vessels. And so, that's why I make this
point of molecular mimicry. Now, in polyarteritis nodosa,
again white blood cells release all these immune peptides and cause destruction of
the blood vessel wall. Damage to the wall causes molecules like collagen and tissue factor, which are normally not exposed to blood, to be released, and when they're released, they interact with clotting
factors in the blood, such as fibrin. Fibrin reacts with the stuff in
the wall of the blood vessels and creates a net-like mesh. This net-like mesh is a clot. So, fibrin is integral in clot formation. Another word you might hear
for clot is thrombosis. Thrombosis is the formation of clots. And so, along with this acute inflammation and clot formation, you can also have old
wounds in blood vessels, where the fibrin has already
tried to patch up the wall. Now, this wall right here is very weak, and so the vessels go through this damage over and over again, and the blood vessel
wall continues to weaken. Now blood vessels, obviously,
are just like pipes, and they're used to
carry blood downstream. If red blood cells, or any other contents, hit the wall of the blood vessel, they're supposed to bounce off and just continue on their merry way. But the problem here is with
a weakened blood vessel, when red blood cells push against this, the wall is so weak that it bulges out. This bulging of the blood vessel
wall is called an aneurysm. It's a weakened part of
the wall that bulges out from the pressure on the
inside of the blood vessel. And lastly, if the blood
vessel wall weakens so much and receives way too much pressure, it can rupture, and this
allows blood to spill out of the blood vessel. In medium size blood vessels, rupture of this can
cause a lot of bleeding, and so rupture is a feared complication of polyarteritis nodosa. Now, if you were to take a
slice of this blood vessel wall and take a look at it under a microscope, you'd be taking a biopsy. That's what a biopsy is, a slice of tissue that you take a look
at under a microscope. And so, in polyarteritis nodosa, we see this fibrinoid necrosis. There are fibrin clots in
the wall of blood vessels and a lot of debris in there
too and cells that are dead. And so, you go through fibrinoid necrosis, and the blood vessels also
go through some scarring, so it's an attempt to try to heal. Once the scar is finished, once the blood vessel has been patched up, this is the process of healing, and so you continue to
go through this cycle over and over and over again, and this continuous process
will cause weakening of the blood vessel walls, and I make this point
because the weakening can get very severe, and the
blood vessels will bulge out, just like I was showing above. These aneurysms appear all
throughout the blood vessel and give its classic appearance. So, this blood vessel wall bulge, blood vessel wall bulge,
blood vessel wall bulge is noted to look like
a string full of beads, and this is actually a classic appearance of polyarteritis nodosa, this
beads on a string pattern. This pattern can be
seen under a microscope, and it can also be seen when you take a look at an arteriogram. This picture right here is
an arteriogram of the kidney. Here's the kidney right here. Kidneys kind of look like
a kidney bean, right? And so, here's blood vessels
that are going through, passing into the kidney,
and if you look closely at the blood vessels,
you can see some of these little dots that are in the blood vessels. These are the nodes. This is the nodularity. There's some here. There's some here. There's one right there. There's one over here. And this isn't very prominent. This arteriogram right
here, which allows you to visualize the inside
of the blood vessels, can actually show very severe aneurysms, very severe bulging of
the blood vessel walls. And so, I'm exaggerating and showing these little black circles, and just like our beads
on a string drawing above, you might see nodularity of
the blood vessels like that, looking like a bead on a string pattern. And so, polyarteritis nodosa
is infamous for causing a lot of damage to many
different medium blood vessels all over the place, blood
vessels in your intestines, blood vessels in the spleen,
blood vessels in the kidneys, blood vessels of the
skin, and it can actually commonly be in the legs as well, even blood vessels serving the nerves or the genitals or the heart. As you can guess, this causes
a wide variety of symptoms. Not only will you get
your generalized symptoms, such as fever, chills, and night sweats, just like any other vasculitis, but also you're getting
local damage of organs. So, damage in the intestines
may lead to bloody diarrhea. Damage to blood vessels
supplying the skin may give you a sort of rash appearance
and other skin lesions. These ulcers are formed because blood isn't supplying the skin as it should. Blood not supplying the heart
can lead to heart attacks. The heart muscle won't contract anymore. If nerves don't get blood, you may see something called neuropathy. Neuropathy means neural
pain or neural issues, and so you might not be able
to move the foot as well, if the nerves supplying
your foot is damaged, or you may feel a tingling sensation or decreased sensations in the foot. Lastly, I wanted to touch on the kidneys. When the kidneys receive
very low blood volume, because remember, these
arteries are being damaged and maybe on the inside it's very narrow, and so blood can't be
delivered to the kidney tissue, when the kidney senses
decreased blood volume, it thinks, oh, I need
to increase pressure, and so, its sensation of
low blood volume makes it go through the
renin-aldosterone-angiotensin system. This system is the kidneys way
to hold onto water and fluid, and so you get an increase
in blood pressure. This increase in blood
pressure, of course, is also known as hypertension. Now, how do you remember all of this? There's so many different
vessels that are damaged. Among all the arteries that are damaged, pulmonary arteries, blood
vessels supplying the lungs, are not damaged. We actually don't know
why this is the case, but this ends up being a
great mnemonic for you, to help you remember this. Polyarteritis nodosa, pulmonary
arteries are not damaged. And treatment is done with
two different medications. Steroids. Steroids inhibit the ability
for white blood cells to communicate with
other white blood cells. So, for example, here's a
part of the blood vessel wall, and let's say this white blood cell wants to cause damage to this wall. It'll also recruit its buddies by sending these molecules to communicate and say, hey, come on over here. However, steroids shut down the communication creation
of these immune molecules. These are called cytokines, by the way. It's a way for cells to communicate, and so, shutting this down prevents more white blood cells
from being recruited to the blood vessel wall, which decreases the
damage of this disease. And cyclophosphamide
is the other medication that's used to treat this disease. Cyclophosphamide acts
to cause damage to DNA. That seems very disastrous. The point of this medication is to target cells that rapidly divide. Immune cells actually go through
rapid growth and division. You have new creation of
immune cells every single day. So, by killing off some of
these rapidly dividing cells, it slows down the immune system. So, by preventing the
cells from causing damage, we slow down inflammation to arteries.