Chapter 25: Bleeding Disorders Caused by Vascular and Platelet Abnormalities

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Welcome back to the Deep Dive.

Today we're tackling a really essential topic, I think, for anyone trying to get their head around clinical hematology.

We're going to be looking at abnormal bleeding,

but specifically the mechanisms that don't involve that classic coagulation cascade everyone learns about first.

That's right.

It's so easy to think about hemostasis, you know, stopping a bleed and immediately jump to things like fibrinogen or factor VIII.

But our focus today, which is Chapter 25, is all about the primary players, the first responders.

We're talking about the blood vessels themselves and, of course, the poitlets.

Right.

Because without them, the whole cascade has nothing to build on, does it?

It has nothing to hold on to.

It's like trying to build a house without a foundation.

So we're really digging into three main areas that cause bleeding problems.

First you have vascular disorders,

second, thrombocytopenia, which is really just a fancy way of saying you have too few platelets, and third, defective platelet function.

And for you, the learner, I think the mission today is to really get the distinctions between these three categories locked in.

Yeah.

Because if you can do that, it's almost a shortcut to getting the diagnosis right.

It really is a shortcut.

We can actually get our bearings right from the start by looking at Table 25 .1.

The pattern of the bleeding, you know, where it's happening, what it looks like, can point you in the right direction before you even get the lab results back.

So what's the big differentiator then?

What's the key thing in that table we need to focus on?

It's all about the location and the type of bleeding.

When we're talking about vascular and platelet disorders, we are almost always talking about mucosal bleeding.

So bleeding gums, frequent nosebleeds, what we call epistaxis or heavy periods, and of course bleeding into the skin.

And that's where we see things like petechiae, right?

Yeah.

The little pinpoint spots.

Exactly.

Petechiae or larger bruises called purpura.

And if you get a little cut, these kinds of defects will cause this persistent annoying oozing that just doesn't want to stop.

And there's another key point in the differential diagnosis here.

These defects, they affect men and women pretty much equally.

Precisely.

Now you contrast that picture with the coagulation disorders, the factor deficiencies we'll get to in the next chapter.

That is a completely different story.

There, you're looking at deep bleeding.

So not skin, but joints and muscles.

Yes.

Bleeding into joints or humerthrosis or into deep soft tissues, which forms these large palpable hematomas.

And because the classic example, hemophilia, is X -linked, you see these disorders overwhelmingly in males.

So it's a simple rule of thumb.

If your patient has petechiae all over their legs, think platelets or vessels.

If they have a swollen, painful knee, you should be thinking about a factor deficiency.

That distinction skin and eucosa versus joints and soft tissue is just fundamental.

It's the bedrock, really.

Before we jump into the diseases, let's just quickly touch on how we grade severity.

T -Bull 25 .2 has the WHO bleeding grades.

Right.

This is just a way for everyone to speak the same language.

It's a scale from 0 to 4.

Grade 0 is simple, no bleeding.

Grade 1 is minor, maybe some petechiae, a little bit of hidden blood loss.

Grade 2 is what we call gross, so visible bleeding.

But it's not serious enough to need a blood transfusion, a nosebleed that stops on its own, for example.

And when does it get really serious?

Where's the cutoff?

Grade 3 is where it gets serious.

That's bleeding, that is severe enough that it requires a transfusion or some other major medical intervention.

And then you have grade 4, that's the life -threatening stuff.

Bleeding into the brain, what we call a CNS hemorrhage, bleeding that causes the patient's blood pressure to crash or any fatal bleed.

Using the scale is just crucial for clinical trials and for making those high -stakes treatment decisions.

Okay, that's a perfect framework.

So with that clinical picture in our minds, let's start with the first group from section 1, the vascular bleeding disorders.

The problem here is the container, not what's inside it.

Exactly, and this is a really diverse group of conditions, what we call heterogeneous.

The basic problem is either in the vessel wall itself or in the connective tissue that's supposed to be supporting it.

And here's a key diagnostic point.

Your standard screening tests, you know, coagulation factors, bleeding time, they're usually completely normal.

And the bleeding itself is generally not super severe.

No, it's typically mild.

It presents as those classic petechiae and ecumoses or bruises.

Let's start with the inherited conditions.

And the first one is a classic,

hereditary hemorrhagic telangiectasia or HHT.

This is one you need to be able to recognize.

Absolutely.

HHT is an autosomal dominant disorder.

It's often caused by mutations in a gene for an endophelial protein called endoglin.

And the hallmark of the disease, the thing you see, is the formation of these telangiectasias.

And what are those exactly?

They're these little dilated microvascular swellings.

They look like tiny red to purple spots and they show up on the skin and on mucous membranes.

If you look at a picture like the one in figure 25 .1a, you'll often see them really clearly on the lips or on the tongue.

They might look a bit alarming, but what's the day -to -day clinical problem they cause?

It's all about chronic blood loss and the anemia that follows.

These little vessels are incredibly fragile, so they lead to these recurrent, sometimes really severe nosebleeds and also bleeding from the gastrointestinal tract.

And this constant, low -grade blood loss just drains the body's iron stores.

So patients often end up with a very severe chronic iron deficiency anemia.

But the real danger isn't the visible stuff, it's deeper, right?

The arteriovenous malformations, the AVMs.

Yes, this is where it gets truly dangerous.

AVMs are abnormal connections, shunts, where arteries connect directly to veins, bypassing the capillary bed.

And these can happen in the lungs, the liver, the spleen, and most critically, in the brain.

Why are the ones in the lungs such a big deal?

Well, the capillaries in our lungs act like a filter.

They catch tiny clots or bacteria.

If you have a pulmonary AVM, that blood bypasses the filter.

So a small clot or a clump of bacteria from somewhere else in the body can go straight through to the systemic circulation and end up in the brain, causing a stroke or a cerebral abscess.

So that's why you absolutely have to screen every single HHT patient for these AVMs in the lungs.

So how do we manage a condition where the pipes are just inherently leaky?

It's a multi -pronged approach.

For specific lesions you can see and get to, you can use things like embolization or laser therapy.

Systemically, we really lean on anti -fibrinolytic drugs like tranexamic acid.

They help stabilize any clot that does manage to form.

And for the really severe refractory cases, we sometimes use anti -VEGF agents like Bevacizumab to try and normalize the vessel growth.

Okay, moving from the vessel wall itself to the scaffolding around it.

The connective tissue disorders.

Right.

Ehlers -Danlos syndromes are the textbook example here.

This is a group of hereditary conditions where collagen synthesis is defective.

And you get this classic triad of features,

joints that are hyper extensible, skin that is hyper elastic but also very friable, and purpura -easy bruising.

And why the bruising?

Is it the vessels themselves again?

Not exactly.

The purpura here is mainly because the platelets can't adhere properly to the faulty subendothelial collagen.

The landing strip is defective, so the platelets can't stick.

And I imagine that makes surgery a nightmare.

A huge red flag.

Poor wound healing and bleeding complications are a major, major concern because the tissues just don't have their normal structural integrity.

We also see another condition called Pseudoxanthoma elasticum, which is interesting because it's linked to both hemorrhage and abnormal arterial thrombosis.

That's a great reminder.

A broken vessel wall doesn't just leak.

It can also cause clots to form where they shouldn't.

It can.

And finally, in this inherited group, we have the rare giant cavernous hemangiomas.

These are big congenital vascular malformations, but what they do to the coagulation system is really unique.

They sort of trap and consume everything locally.

That's a perfect way to put it.

The blood flow inside these things is really sluggish, so you get this chronic localized activation of the coagulation cascade.

Platelets and factors get used up inside the hemangioma, and the lab results can sometimes look a lot like disseminated intravascular coagulation, or DIC, and it can cause a pretty severe thrombocytopenia.

Okay, let's switch gears to the acquired vascular defects.

These are things you are much more likely to see in general practice.

Definitely.

And we can start with something that's benign and extremely common.

Simple, easy bruising.

You see this all the time in healthy women of childbearing age.

And then there's senile purpura.

The images of senile purpura, like in figure 25 .1b, are very distinct.

It's usually on the back of the hands and forearms.

Yes, and that's because it's caused by age -related atrophy.

The supporting connective tissue and fat right under the skin thins out over time, so the little cutaneous blood vessels are left really unprotected, and they can tear with just minor trauma.

Moving on to infections.

How can a bug cause purpura?

A few different ways.

The infection itself, whether it's bacterial or viral, can directly injure the vessel wall.

Or the infection can set off a systemic process like DIC, leading to massive consumption of platelets and factors.

Or, and this is a key mechanism, it can trigger the formation of immune complexes.

Antigen antibody complexes that just deposit in the vessel walls.

Exactly.

They deposit there, cause inflammation of vasculitis, and the vessels start to leak.

You see this in things like measles, or in its most dangerous form, in meningococcal septicamia.

And that mechanism leads us perfectly to the classic example of this, Hanauk -Schunlein syndrome, or as it's more properly called now, IgA vasculitis.

Right.

This usually affects children, and it often comes on after an upper respiratory infection.

The core problem is in IgA -mediated vasculitis.

These IgA immune complexes deposit in small vessels and cause all the trouble.

So, what are the key clinical features?

Figure 25 .2 shows the classic rash.

There's a sort of clinical pentad you look for.

First, that characteristic prepuric rash.

It's non -blanching, meaning it doesn't fade when you press on it, and it's most prominent on the buttocks and the lower legs.

Second, you get localized swelling, or edema.

Third, painful joints.

Fourth, abdominal pain, which can be quite severe.

And fifth, hematuria, blood in the urine, which tells you the kidneys are involved.

And that kidney involvement is why you have to follow these kids up, right, even if they seem to get better.

Absolutely.

Most of the time, it's self -limiting and just goes away.

But there is a real risk of progressive renal failure in a small number of patients, so you have to keep an eye on them.

Let's touch on a nutritional cause, Scroovy.

It's rare now, but it's such a perfect example of how collagen is linked to bleeding.

It really is.

Scroovy is just vitamin C deficiency, and vitamin C is essential for making healthy collagen.

So without it, you get defective collagen synthesis, and this shows up as paraphilicular petechiae, these little hemorrhages right around the hair follicles.

You also get bruising and bleeding gums.

Figure 25 .1c shows that pattern really well.

And finally, a very common cause we see in the hospital,

steroid purpura.

Yes.

Long -term use of high -dose steroids, or the steroid excess you see in Cushing's syndrome, really messes with the integrity of the vascular -supportive tissue.

Just like in senile purpura, the vessels are left unsupported, and they just tear with minimal trauma.

Before we move on from vessels, let's just circle back to that really important management point about anti -fibrinolytic drugs.

Drugs like tranxamic acid are great.

They stabilize the fibrin clot, and they reduce bleeding.

But you have to be incredibly careful, and in fact, they're often contraindicated, if your patient has hematuria, so blood in their urine.

Why is that so dangerous?

You'd think stabilizing a clot would be a good thing everywhere.

You would, but if you stabilize a clot inside the urinary tract, you can create this big, solid, stable plug that physically obstructs the ureter or the kidney.

And that can lead to acute kidney injury.

It's a classic case of the treatment being worse than the disease.

You solve the bleeding, but create a plumbing catastrophe.

That is such a critical teaching point.

Okay, let's make a conceptual shift now, from the integrity of the vessel wall to the number of plugs we have, on to section two, thrombocytopenia.

So now we're dealing with a low platelet count, and the clinical picture is basically the same.

Skin purpura, mucosal hemorrhage, prolonged bleeding after an injury.

And we can divide the causes into three main baskets, failure of production, increased destruction or consumption,

and abnormal distribution.

Let's start with failure of production in the bone marrow, which the text says is the most common cause overall.

Right.

And usually this happens as part of a bigger problem, a generalized bone marrow failure where multiple cell lines are down.

You see this with cytotoxic chemotherapy, with radiation in a plastic anemia, or when the marrow is just crowded out by things like leukemia, MDS, or infiltration by other cancers.

We should probably also mention some common non -cancer causes.

Definitely.

Things like megaloblastic anemia from B12 or folate deficiency can suppress production.

And HIV infection is another important cause.

So that's generalized failure.

But sometimes the problem is more specific, just hitting the megakaryocytes, the platelet factories.

That's right.

You can get selective depression from suit and drugs or viruses.

But it's also the hallmark of some rare but important congenital defects.

Like problems with the thrombo -pointing pathway, the main signal for platelet production.

Exactly.

The CMPL gene codes for the TPO receptor.

If you have mutations there, the megakaryocytes don't get the GO signal to grow and mature, so production is low.

There are others too, like mutations in the RBMAA gene, which you sometimes see in a syndrome with absent radii.

And then there are those fascinating genetic syndromes that affect more than just platelets.

Right.

Like the MYH9 -related disorders, which includes the May -Hegelin anomaly.

In these conditions, patients have a low platelet count, and their platelets are characteristically very large.

But the clue is that you also see these big distinctive inclusions inside their granulocytes.

It tells you the defect is affecting multiple cell lines.

Wiscot -Aldrich syndrome is another one that's a multi -system disorder.

WAS is caused by a mutation in the WASP gene.

The thrombocytopenia is often severe with small dysfunctional platelets.

But it's really defined by the classic triad – thrombocytopenia, eczema, and a serious immune deficiency.

If you see that constellation of symptoms, you need to be thinking about WAS.

Okay.

A really common clinical scenario where we see a low platelet count is chronic liver disease.

And the text points out there are two things happening at once here.

Yes, the liver is central to this.

First, as the liver fails, it stops producing enough thrombopoietin, or TPO, so that's a direct hit on production.

Second, if the patient develops portal hypertension and their spleen gets really big splenomegaly, then you run into the problem of abnormal distribution, which is our next category.

And there's a specific treatment now that targets that production deficit.

There is.

For patients with chronic liver disease who need to have a procedure, a TPO mimetic called Avatrombopag can be used.

It's licensed specifically to boost the platelet count before a procedure to reduce the bleeding risk.

So that brings us to the second basket of causes.

Abnormal distribution of platelets.

And this is almost all about the spleen.

Splenomegaly is the major player here.

In a normal person, about a third of all your platelets are just hanging out or sequestered in the spleen at any given time.

But if you get massive splenomegaly, say from liver disease or a hematologic cancer, that number can go way up.

Up to 90 % of the total platelet mass can end up pooled in the spleen.

Figure 25 .9 illustrates that really well.

90 % sounds catastrophic.

But here's the key clinical question.

Does that pooling by itself usually cause bad bleeding?

And the answer is it usually does not.

The key thing to understand is that the platelets lifespan is still normal and the platelets that are actually circulating are perfectly functional.

It's a distribution problem, not a destruction problem.

So you really only see significant bleeding if there's another problem on top of it, like the low production you also get in liver failure.

And the last sort of mechanical cause here is dilutional loss.

This one is pretty straightforward.

Yeah, this happens during a massive transfusion.

So if a patient gets more than, say, 10 units of stored blood in 24 hours, stored packed red cells don't have any viable platelets.

So you're just diluting the patient's own platelets down to a dangerously low level.

You have to actively replace them with platelet transfusions and also give FFP to replace the clotting factors.

Okay, finally in this section we have to talk about drugs.

Drug or toxin -related thromocytopenia, table 25 .4, list a whole bunch.

Right, and we can split them into two groups.

You have the predictable ones, things that are just directly toxic to the bone marrow in a dose -related way.

So ionizing radiation, chemo drugs, and alcohol.

And then you have the much more unpredictable immune -mediated mechanisms.

And what are the common culprits for immune destruction?

Oh, the list is long.

Analgesics, anti -inflammatories, antibiotics like penicillins and sulfonamides, diuretics.

But the one you absolutely have to know inside and out, especially in the hospital setting, is heparin.

Because that leads to heparin -induced thrombocytopenia, or HIT, which is a whole complex and dangerous entity in itself.

All right.

We've covered production failure and distribution issues.

Let's move on to the most dynamic set of problems in section three.

Increased destruction of platelets, starting with the classic autoimmune thrombocytopenic purpura, or ITP.

Yes, ITP.

This is the most common cause of an isolated thrombocytopenia.

And what we mean by that is that only the platelet count is low.

The red cells and white cells are normal.

Historically, we thought of it as a disease of young women.

But we now know the incidence actually increases with age.

Let's walk through what's actually happening here.

Figure 25 .4 lays out the pathogenesis.

It's a textbook type two hypersensitivity reaction.

It is.

It all starts with the body making autoantibodies, usually IgG, that target proteins on the platelet surface.

The main targets are glycoproteins, like GPI -BIAR, the GPI complex.

Once these antibodies coat a platelet, that platelet is effectively flagged for destruction.

And the spleen is the executioner.

The spleen is the main site of destruction.

Macrophages in the spleen have receptors that recognize the FBC portion of that IgG antibody.

They grab onto it and they just gobble up the platelet, phagocytosis.

So normal platelet lives for about 10 days.

How short does it get in ITP?

It can be reduced to just a few hours in severe cases.

But the body doesn't take this lying down.

The bone marrow senses the low count and it goes into overdrive.

It ramps up platelet production, increasing the total megakaryocyte mass by up to five times, just trying desperately to keep up.

And that explains some of the key clinical features of ITP.

It does.

The onset is often slow and insidious.

Easy bruising, petechiae, heavy periods.

The big fear is intracranial hemorrhage, but thankfully that's very rare.

And here's a really important clinical pearl.

The bleeding is often less severe than you would expect for such a low platelet count.

Why is that?

Why do they bleed less?

Because the platelets that are managing to survive in circulation are the young ones, fresh from the bone marrow.

And these young platelets are larger and they are functionally hotter, they're more active.

Also, a key physical finding is a non -palpable spleen.

If the spleen is enlarged, you should be very suspicious that the ITP is actually secondary to something else, like lymphoma or HIV.

So the diagnosis is really one of exclusion.

Exactly.

The platelet count is usually somewhere between 10 and 100.

The blood film is critical.

You'll see fewer platelets, but the ones that are there are often large.

The other cell lines are normal.

A bone marrow biopsy would show normal or increased numbers of megakaryocytes.

And while you can test for the anti -platelet antibodies, it's not standard practice.

We usually treat based on the clinical picture.

Now, the treatment strategy for chronic ITP is interesting, because the goal isn't necessarily to get the count back to normal.

No, not at all.

The goal is safety.

We just want to get the platelet count above the level where spontaneous bleeding is a risk, so usually above 20.

And we want to do that with the minimum amount of treatment to avoid long -term side effects.

So what's the first -line therapy, and why does it work?

First line is corticosteroids.

Usually high -dose oral prednisolone or a short, sharp pulse of high -dose dexamethasone.

They work by suppressing the immune system, so they reduce the production of the auto antibodies, and they also partially block the macrophages in the spleen from eating the platelets.

You get a good response in about 80 % of patients.

What if you need the count to come up right now, like in a life -threatening bleed?

That's when you need high -dose IV immunoglobulin, or IVIG.

This stuff is amazing.

It can bring the platelet count up rapidly, often within 24 hours.

The mechanism is really clever.

You're flooding the system with so much normal IgG that it just saturates all the Xe receptors on the macrophages, so they're too busy dealing with the IVIG to notice the patient's antibody -coated platelets.

It's a temporary fix, but it can be life -saving.

If steroids fail or the patient can't tolerate them, what's next?

We often move to more targeted therapies, where Tuximab is a monoclonal antibody that targets CD20 on B cells, wiping out the cells that are making the antibodies.

That gives a good, durable response in a lot of patients, and we often try it before thinking about splenectomy.

And then we have the newer drugs, the TPO receptor agonists,

the thrombomimetics.

Yes.

These are drugs like romeplastum, which is an injection, and eltrombopag, or avitrombopag, which are oral.

These are usually for patients who don't respond to steroids.

And they work by mimicking thrombo -poietin, so they directly stimulate the megakaryocytes to just churn out massive numbers of new platelets.

You're basically outproducing the destruction.

Figure 25 .5 shows a beautiful response to these drugs.

If they're so good at boosting production, why aren't they used first line?

Why bother with steroids?

That's a great question.

It comes down to a few things.

Long -term safety data is one, and there's a specific concern that long -term use can cause some reversible fibrosis in the bone marrow.

Plus, they don't actually treat the underlying autoimmune disease, they just overwhelm it.

And they're also very expensive.

What about splenectomy?

That used to be the main second line option.

It did.

And it works well, giving a durable remission in 60 to 80 % of patients because you're removing both the main site of antibody production and the main site of platelet destruction.

But its use has really gone down now that we have Rituximab and the TPRAs, which are obviously less invasive.

And for the really tough refractory cases.

Then you're into more heavy -duty immunosuppressants like cyclophosphamide or vincristine.

There's also a newer drug called Fostimatinib, which is a SYK inhibitor that blocks some of the immune signaling pathways.

Let's just quickly contrast chronic ITP with the acute form we see in kids.

Right.

Acute ITP in children often follows a trigger, like a viral illness, chickenpox is a classic one or a vaccination.

And the key difference is the prognosis.

In kids, 90 to 95 % of cases will resolve completely on their own.

Spontaneous remission.

So you can often just watch and wait.

You can.

We usually only treat if the count is dangerously low, say below 10, or if there's significant bleeding.

Because even though treatment like IVG makes the count come up faster, it doesn't actually change the excellent long -term prognosis.

Okay, let's shift to another type of immune destruction, the drug -induced kind.

Figure 25 .6 shows the mechanism, and it's a bit different from ITP.

It is.

In ITP, the antibody attacks the platelet directly.

In drug -induced cases, the drug itself is part of the problem.

What happens is an antibody -drug complex forms in the blood, and that whole complex then sticks onto the surface of the platelet.

This then leads to the platelet being either destroyed by complement or cleared by macrophages.

So the treatment is obvious in theory.

In theory, yes.

Stop the offending drug immediately.

The platelet count can drop incredibly fast, so platelet transfusions are only used if there's dangerous bleeding, because the transfused platelets will likely be destroyed very quickly as well.

Okay, one last rare one in this category.

Post -transfusion prepara.

This is a really severe thrombocytokinia that happens about 10 days after a blood transfusion.

It's usually because the recipient makes antibodies against a platelet antigen, most commonly HPA1A, that was on the transfused platelets.

But the weird and fascinating part is that these antibodies somehow also trigger the destruction of the patient's own platelets, even though they lack that antigen.

An innocent bystander effect.

A very dangerous innocent bystander effect.

The treatment is high -dose IV edge.

Okay, we've covered immune consumption.

Now for section 4, a truly terrifying group of disorders.

The thrombotic microangiopathies, TDP and HUS.

This is where destruction meets thrombosis.

Yes, these are medical emergencies.

They are syndromes characterized by widespread clot formation in the tiny blood vessels, the microvasculature.

And this process consumes huge numbers of platelets, and it also mechanically shreds red blood cells as they try to squeeze past the clots.

Let's focus on thrombotic thrombocytopenic purpura, or KTP.

This all comes down to one enzyme, a molecular scissors called ADMTS -13, figure 25 .7 illustrates this perfectly.

Right, so normally von Willebrand factor is released from endothelial cells in these huge ultralarge multimeric strings.

And these strings are incredibly sticky.

The job of the ADMTS -13 protease is to circulate around and snip these ultralarge VWF multichemers into smaller, less sticky pieces.

It's a crucial safety mechanism.

And in TTP, that safety mechanism fails.

It fails completely.

In acquired TTP, which is the common form, the patient develops an autoantibody that inhibits ADMTS -13.

In the rare familial form, the gene for the enzyme is just defective.

And the result is that these ultralarge, hyper -sticky VWF strings persist in the circulation.

And what do these sticky strings do?

They anchor themselves to the endothelium and act like long strands of fly paper streaming through the microvasculature.

Platelets passing by stick to them instantly via their GPI receptors, and you get the formation of these occlusive, platelet -rich thrombi.

These thrombi then break off and block small vessels all over the body, causing organ damage from ischemia.

Figure 25 .8a actually shows one of these thrombi in a cardiac vessel.

Clinically, TTP is known for its classic pentad of symptoms, although you don't always see all five.

No, you rarely do.

But the pentad is, one, pharmacidopenia, two, microangiopathic hemolytic anemia, or MAHA, three, neurological problems, which can be anything from a headache to a seizure or a stroke, four, renal failure, and five, fever.

The MAHA is from the web cells being physically ripped apart as they're forced past the fibrin strands in the clogged vessels.

And that gives us the key lab findings that should set alarm bells ringing.

Absolutely.

You see a profound thrombocytopenia.

And the blood film, shown in Figure 25 .8b, is full of schistocytes, these fragmented, helmet -shaped red cell pieces that are the hallmark of MAHA.

And your LDH, lactate dehydrogenase, will be sky high, both from the destroyed red cells and the ischemic tissue.

And what's the one lab test that separates TTP from DIC, the other big clotting catastrophe?

The coagulation screen.

In TTP, the PT and APT are characteristically normal.

This is the absolute key differentiator.

In DIC, the clotting factors are consumed, so the clotting times are prolonged.

You have to start treatment for TTP based on suspicion alone.

You can't wait for the specific Adam TS13 level to come back because the mortality without treatment is close to 90%.

So what is that life -saving treatment?

Urgent plasma exchange, or PEX.

You use fresh -frozen plasma as the replacement fluid.

And this does two critical things at once.

It physically removes the bad stuff, the antibody and the ultra -large VWF multimars, and it simultaneously replenishes the good stuff, the functional Adam TS13 from the donor plasma.

You then follow the platelet count and the LDH to see if it's working.

And we have better therapies now to go along with PEX.

We do.

Rituximab is now used almost routinely to kill off the B cells making the antibody and reduce the risk of relapse.

And we also have capylcesiumab, which is an antibody against VWF itself.

It works by physically stopping the platelets from sticking to the VWF strings, which can lead to a much faster resolution of the acute episode.

Now for the most important management point in this entire section, the one thing you must never, ever do.

Platelet transfusions are absolutely and unequivocally contraindicated in TTP and HUS.

If you give more platelets, you are literally throwing fuel on the fire.

You will worsen the thrombosis and accelerate the organ damage, especially the neurological damage.

It is a fatal error.

Let's just briefly contrast TTP with haemolytic uremic syndrome, or HUS.

HUS has the same MAHA and pharmacidopenia, but the organ damage is usually pretty much confined to the kidneys, often causing severe renal failure.

The typical form of HUS is associated with diarrheal illness caused by E.

coli O157 verotoxin.

But there is also an atypical HUS, which is related to uncontrolled activation of the complement system.

And the treatment is different.

For typical HUS, it's mainly supportive care dialysis for the kidneys, managing blood pressure.

For atypical HUS, you can use a targeted complement inhibitor like aculizumab.

Okay, what a journey.

We've gone from the vessel wall to the number of platelets to their destruction.

Now for the final piece of the puzzle in section 5, disorders of platelet function, the quality of the plug.

Right.

So you should suspect a functional or qualitative defect when your patient has the classic skin and mucosal bleeding.

But their platelet count is normal, and their VWF levels are also normal.

The platelets are there, they just aren't working right.

Let's start with the rare inherited defects, because there's such good teaching models for how platelets are supposed to work.

The first one is Glansman's thrombesthenia.

This is an autosomal recessive disorder where there are mutations in the genes for GPI or

This complex is the final step for platelet aggregation.

It's what binds fibrinogen to link platelets to each other.

So in the lab, these platelets fail to aggregate in response to any agonist you throw at them, except for one.

And that one exception is ristocetin.

Exactly.

Because ristocetin tests the first step, adhesion, which involves VWF binding to a different receptor, GPI.

That part is normal in Glansman's.

The next condition is Bernard -Salina syndrome.

This is also autosomal recessive, but here the mutation is in the GPI gene, the VWF receptor.

These platelets are huge, much larger than normal.

And because they're missing the VWF receptor, they fail to aggregate specifically in response to ristocetin.

Then you have the storage pool diseases where the platelets are missing their internal cargo.

Right.

They are missing the contents of their granules, the little packets of chemicals like ADP and fibrinogen that they need to release to call for backup and amplify the response.

So for example, in gray platelet syndrome, the alpha granules are absent.

In delta storage pool disease, the dense granules are missing.

The platelets stick, but they can't signal properly.

And of course, the most common inherited bleeding disorder of all, l 'Onwilibren disease, is really a platelet -dependent problem because the defect is in the VWF protein itself.

It is, but the key takeaway for this whole section is that the functional problems you will actually see in your clinical practice are far more likely to be acquired than inherited.

And the number one cause of acquired functional defects is antiplatelet drugs,

aspirin being the classic example.

You have to understand aspirin.

It works by irreversibly inhibiting an enzyme called cyclooxygenase, or COX.

COX is needed to make thromboxane Aeros, which is a powerful signal for platelet activation and aggregation.

And because that inhibition is irreversible, that platelet is basically knocked out for its entire 7 to 10 -day lifespan.

How is that different from what N -acides like ibuprofen do?

N -acides also inhibit the kyax enzyme, so they also cause defective function and bruising.

But the crucial difference is that N -acides cause reversible inhibition.

As soon as the drug is cleared from the body, the platelet function returns to normal.

This is a really important distinction if a patient needs surgery.

Then we have the newer drugs that target the ADP pathway.

The P2Y12 inhibitors, like clopidogrel and ticagrelor, these are hugely important drugs for preventing thrombosis, especially after someone has a coronary stent put in.

They work by blocking ADP from binding to its receptor on the platelet surface.

And the most powerful drugs, the ones used in acute heart attacks.

Those are the GPI -BIA inhibitors epsiximab, eptifibatide.

These are IV drugs that directly block the final common pathway, the fibrinogen receptor itself.

They are incredibly potent.

And we can actually see how these drugs affect function using platelet aggregation tests, like in figure 25 .10.

Yes, these tests are fantastic.

You take the patient's platelets, add an agonist like ADP, and watch how they clump together.

A patient on aspirin will have a blocked secondary wave of aggregation because the release reaction is poisoned.

A patient on clopidogrel will show a specific defect only when you stimulate them with ADP.

It's how we can really dissect what's going wrong.

And just quickly, what other medical conditions can cause acquired platelet dysfunction?

A few important ones.

Chronic kidney failure, or uremia, is well known to cause platelet dysfunction.

Hyperglobulinemia, like you see in multiple myeloma, the excess protein can physically coat the platelets and stop them from working.

And many of the myeloproliferative and myelodysplastic disorders come with inherently dysfunctional platelets.

Okay, we have established all the mechanisms.

Let's pull it all together in section six.

Diagnosis and management principles.

Right.

The whole diagnostic approach is laid out nicely in the flowchart in figure 25 .11, and it all starts with the basics.

A full blood count and, critically, a look at the peripheral blood film with your own eyes.

Why is looking at the film yourself so important?

Because of the classic trap for new players, pseudothrombocytopenia.

This is a lab artifact.

The EDTA anticoagulant in the purple top tube can cause some people's platelets to clump together in the test tube.

The machine sees these big clumps as single cells and reports a falsely low platelet count.

So what do you do if you suspect that?

You have to repeat the count in a different tube, usually a light blue top with citrate or a green top with heparin.

If the count normalizes, problem solved.

The patient is fine.

But if the low count is real, then you look at the film.

A low count with big platelets screams ITP or another consumptive process.

And when do you have to do the more invasive tests, the bone marrow biopsy?

You have to do it whenever you suspect a production problem.

So in an older patient where you need to rule out MDS or leukemia, or if other cell lines are also low.

If it's a young, otherwise healthy patient with isolated thrombocytopenia, you can often be confident it's ITP and hold off on the marrow.

But any doubt about production, you have to look.

Now if the platelet count is normal, your whole diagnostic pathway shifts.

It shifts completely.

Now you're thinking about a functional problem.

So you start with a screening test, like the PFA 100.

If that's abnormal, you move on to the detailed platelet aggregation studies with all the different agonists.

That's how you can tell the difference between something like glansmans and just a patient who took an NSAID.

And if you're thinking von Willebrand disease.

Then you need to order the specific assays for VWF, antigen, and factor VIII activity.

It's a very logical step -by -step process.

Let's just briefly revisit the thrombomimetic drugs, the TPORAs.

Right.

Romyplastum.

L -TrumboPag.

They work by activating the TPO receptor and just forcing the marrow to make more platelets.

And it's important to remember they're not just for ITP.

They're also used for thrombocytopenia in MDS, aplastic anemia, and in liver disease.

They are a powerful tool whenever you need to boost production.

And finally, a quick word on platelet transfusions.

When do we use them and what are the targets?

We use them for two main reasons.

One, to treat active, significant bleeding that we can't control otherwise.

Or two, prophylactically,

before an invasive procedure like a liver biopsy or a lumbar puncture in a patient with a very low count.

And what are the target counts we're aiming for?

For a big invasive procedure, we generally want the count to be above 50.

For general prophylaxis in a patient with bone marrow failure, the traditional threshold is to transfuse when the count drops below 10.

However, if that patient has other risk factors, like a fever, an infection, or a coagulopathy, we usually raise that threshold to 20 just to be on the safe side.

This has been an incredibly thorough deep dive.

Let's wrap up with the absolute must -know take -home concepts.

I think the first and most important one is that clinical distinction.

Platelet and vascular problems give you skin and mucosal bleeding petechiae.

Coagulation factor problems give you deep tissue and joint bleeding hematomas.

Pattern recognition is your best friend.

And when you're thinking about platelet destruction, remember the two big, very different autoimmune problems.

ITP is an autoimmune consumption problem that you treat with immunosuppression, like steroids or rituximab, or you boost production with TPO or ACE.

And TTP is a dangerous microvascular thrombosis problem from Adam T13 deficiency that requires urgent plasma exchange.

And always, always remember the life -saving rule.

You do not give platelets in TTP.

Finally, when it comes to platelet function, remember to think horses, not zebras.

Acquired defects, especially from drugs like aspirin and NSAIDs, are infinitely more common than the rare inherited diseases like Glansman's thrombostinia.

Absolutely.

The bread and butter of platelet dysfunction is drugs and systemic diseases.

So we'll leave you with this provocative thought to mull over.

A patient comes to you with just some nonspecific purpura and easy bruising.

Their platelet count is normal.

Their coagulation screen is normal.

Knowing that a simple drug history is far more likely to give you the answer than a rare congenital disease.

What specific questions would you prioritize in your history taking to find the cause before you even think about ordering a battery of expensive specialized tests?

That patient's medication list, including everything over the counter, is the single most valuable piece of diagnostic information you can get.

Absolutely.

Thank you for joining us for this really essential deep dive into the world of vascular and platelet bleeding disorders.

We hope this gives you a clear roadmap for thinking about these complex conditions.

We'll catch you next time.