Vasculitis

With vasculitis, you have “inflammation”, of the “blood vessels”, and even though this can happen in arteries or veins, we’re going to focus on vasculitis in arteries because it’s way more common.

Vasculitides—plural for vasculitis—are categorized by the size of the blood vessels they affect, so we have small-vessel, medium-vessel, and large-vessel vasculitis.

Typically vasculitis is due to an autoimmune disease, where the immune system confuses a part of normal body as a foreign invader, and there are a couple of ways this might happen.

Sometimes the body confuses the innermost layer of the blood vessel, which is the endothelial layer, with a foreign pathogen and directly attacks it.

To be a little bit more specific, the white blood cells of the immune system mix up the normal antigens on the endothelial cells with the antigens of foreign invaders like bacteria simply because they look similar—and this is called molecular mimicry.

This autoimmune confusion is thought to be the cause several types of medium-vessel and large-vessel vasculitides.

Other times the immune system attacks healthy cells that are near the vascular endothelium, and the endothelial cells are only getting indirectly damaged.

This is the situation in many small-vessel vasculitides, where the immune system attacks white blood cell enzymes or other non-endothelial cell targets.

Once the endothelium is damaged either directly or indirectly, almost all vasculitis diseases progress in a similar way.

The damaged endothelium exposes the underlying collagen and tissue factor, and these exposed materials increase the chance of blood coagulation.

The blood vessel walls themselves get weaker as they’re more damaged, making aneurysms more likely.

And finally as the vessel wall heals, it becomes harder and stiffer because fibrin is deposited into the vessel walls as part of the healing process.

And actually, that’s vasculitis in a nutshell.

The different types of vasculitis for the most part only vary depending on how they are triggered and where in the body they cause problems.

People with vasculitis have generalized symptoms caused by the inflammatory response of the immune system.

Symptoms like fever, weight loss, fatigue, and so on.

More specific symptoms occur usually based off where in body the vasculitis is occurring, and which organ is supplied by that blood vessel.

When vasculitis happens in those blood vessels, you get reduced blood flow in those organs, called organ ischemia, which can happen in two ways.

First, blood cells clump onto the exposed tissue factor and collagen on the inside of blood vessels forming blood clots that and can restrict blood flow.

The second way is caused by the healing process of the blood vessel.

As fibrin is deposited in the vessel wall, the walls become thicker and bulge into the vessel, reducing the diameter of the vessel lumen, and restricting blood flow.

Alright, now that we have the general idea of vasculitis covered, let’s take a look at some specific conditions, starting with the large-vessel vasculitides.

Giant cell arteritis is a vasculitis that affects branches of the carotid arteries.

Vasculitis in the temporal branch of the carotid artery is the most common location and causes headaches.

Vasculitis in the ophthalmic artery can cause visual disturbances, and vasculitis in any of the arteries that supply the jaw muscles can cause pain when someone chews food—called claudication.

Giant cell arteritis affects older individuals (typically more than 50 years old) and women more than men, so a grandmother would be in a high-risk group.

Classically, this type of vasculitis causes lots of inflammation and it results in a really high erythrocyte sedimentation rate (or ESR for short)—sometimes over 100!

In giant cell arteritis, a biopsy of the affected artery will show giant cells embedded in the internal elastic lamina, which is a thin layer of elastic tissue that separates the tunica intima and the tunica media.

To be clear, these giant cells are actually not individual cells at all, but rather a group of monocytes that are packed tightly together, and look like one giant cell.

Now giant cell arteritis is segmental, meaning that if you look at the entirety of an affected artery, you’ll see only sections of the artery that are actually affected.

This means that when biopsies are done, you have to take a long section of the artery and examine it under a microscope.

It also means that, if you don’t see any affected tissue, you can’t for sure rule out the disease because it’s possible you took an unaffected section of the blood vessel.

You can treat people with giant cell arteritis by giving them corticosteroids, which weakens the immune response.

People whose ophthalmic artery is affected and don’t receive treatment are at a high risk of blindness, again because poor blood flow to the eyes causes ischemia and irreversible blindness.

Alright, so another type of large-cell vasculitis is called Takayasu Arteritis, and it’s very similar to giant cell arteritis except for two key differences.

One is that it usually affects asian women that are under 40 years old where giant cell arteritis usually affects people over the age of 50.

And two, it affects the arteries that branch off from the aortic arch, particularly around the branch points.

If the inflammation happens around aortic branches that serve the upper extremities, it can cause weak or nonexistent pulse.

If the inflammation happens around the aortic branch that serves the head, then it causes visual and neurological symptoms.

Histopathologically it’s pretty similar to Giant cell arteritis because in Takayasu Arteritis you still see giant cells and granulomatous inflammation in the internal elastic lamina of the blood vessel.

In addition, the erythrocyte sedimentation rate will be elevated, and Takayasu arteritis is treated with corticosteroids.

Alright, so now let’s move onto medium-sized vasculitis diseases.

These vasculitis diseases typically affect a wide range of muscular arteries that supply organs, which gives the conditions a wide range of possible symptoms.

The most common type of all vasculitides is Kawasaki disease, and we’ve got a separate video on Kawasaki disease, but for now it’s important to note that it affects the coronary arteries, the muscular arteries serving the heart.

Next there’s polyarteritis nodosa, which is thought to occur when the immune cells directly attack the endothelium, confusing it with hepatitis B virus.

Now, polyarteritis nodosa causes transmural inflammation, which means the entire wall, the tunica intima, the media, and the adventitia are all affected.

The inflammation causes the vascular wall to die through all three layers of the artery and fibrosis occurs as the vascular wall heals, and this process is called fibrinoid necrosis.

The fibrosed vessel wall is left weak and prone to aneurysms, so some areas start to bulge out through the weakened walls.

So if you step back and look at the artery you see these fibrotic aneurysms which are hard bulges down the length of the artery, and they look like a “string of beads” on angiogram.

This pattern is pretty unique among the various vasculitides.

Organ ischemia in the distribution of affected arteries is the main complication.

If the renal arteries are affected, then a person will have hypertension (because remember kidneys regulate blood volume).

If the mesenteric artery is affected, a person can have mesenteric ischemia and severe abdominal pain and gastrointestinal bleeding.

If the arteries supplying the brain are affected it can cause neurological symptoms, and if arteries supply the skin are affected then it can lead to skin lesions.

Treatment is aimed at reducing the vessel inflammation and generally includes corticosteroids as well.