Immune thrombocytopenic purpura - causes, symptoms, diagnosis, treatment, pathology

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Immune thrombocytopenic purpura, or ITP, is an autoimmune condition in which the body

produces antibodies against its own thrombocytes or platelets, which are destroyed, and this

results in purpura, or small bleeding spots beneath the skin.

Normally, when there is any kind of damage to the blood vessel, hemostasis occurs, which

is the process that stops the bleeding and plugs the damaged vessel to limit the blood

loss, and there are two steps, primary and secondary hemostasis.

During primary hemostasis, platelets aggregate to form a plug at the site of the injured

blood vessel.

Platelet aggregation is mediated by surface proteins found on platelets, called GP2b3a

receptors.

While these platelets are aggregating, secondary hemostasis kicks in.

Secondary hemostasis is also called coagulation because that's when clotting factors come

into play one after another, with the ultimate goal of cleaving fibrinogen into fibrin.

Then, fibrin forms a protein mesh, kind of like a giant net, that covers the platelet

plug and stabilizes it.

Now in ITP, the spleen produces certain IgG autoantibodies, which bind to the platelet

receptor GP2b3a and targets the platelet antibody complexes for destruction in the spleen.

This leads to lowering of platelet counts in the blood, which makes it harder for bleeding

to stop.

Now ITP can be acute or chronic.

Acute ITP usually affects children a couple weeks after a viral infection and resolves

spontaneously within two months.

Chronic ITP usually affects females of reproductive age and persists more than six months.

Chronic ITP can also be primary when it occurs without an underlying trigger, or secondary

when it's triggered by another condition like hepatitis C, HIV, or lupus.

Most of the time, ITP is asymptomatic.

In some cases, it can cause purpura, which are red or purple spots on the skin, measuring

0.3 to 1 centimeter in diameter.

In severe cases of ITP, when platelet levels get very low, there may be frequent mucosal

bleeding, which most commonly presents as epistaxis, meaning nosebleeds.

ITP is a diagnosis of exclusion, so there is no specific test that confirms the diagnosis.

Interestingly, the CBC usually shows isolated thrombocytopenia with a normal hematocrit

and leukocyte count.

Now, in some cases, if there is significant bleeding, that can lead to anemia.

An abdominal ultrasound is often done to rule out splenomegaly, and hepatitis C virus

and HIV testing are done to rule out secondary ITP.

Individuals with secondary ITP are treated for their underlying condition, while treatment

of primary ITP depends on the platelet count and symptoms.

Asymptomatic patients with a platelet count over 30,000 can be observed and often recover

on their own.

Patients with an active bleed or those with a platelet count below 30,000 are usually

started either on corticosteroids or intravenous immunoglobulin, or IVIG for short.

Corticosteroids act as immunosuppressants, and IVIG has an immunomodulatory effect.

Both of them help stop the formation of new autoantibodies.

In individuals who don't respond to steroids, a splenectomy can be done to get rid of the

splenic macrophages that are destroying the platelets.

Finally, transfusing platelets can be done when platelet count is less than 10,000.

All right, as a quick recap, ITP is a condition where the spleen produces IgG autoantibodies

against the platelet receptor GP2B3A, which leads to destruction of platelets.

Acute ITP lasts for less than two months and usually affects children.

Asymptomatic ITP lasts more than six months and usually affects females of reproductive

age.

Most of the time there are no symptoms, but sometimes individuals with ITP can have purpura

or even nosebleeds in some severe cases.

In general, asymptomatic ITP resolves on its own, but severe cases are treated with corticosteroids

or intravenous immunoglobulin.