Immune thrombocytopenias: ITP and HIT
- Lesion
Antibodies coat platelets so the spleen removes them. Most cases bleed; one drug reaction, heparin-induced, clots instead.
What it is
Immune thrombocytopenias are caused by antibodies that shorten platelet survival. Chronic immune thrombocytopenic purpura (ITP) is mostly a disease of adult women, with IgG autoantibodies against GPIIb/IIIa or GPIb/IX; it may be primary or secondary to lupus, HIV or CLL. Acute ITP is a self-limited disease of children after a viral infection. Drugs such as quinine, quinidine and vancomycin trigger drug-dependent antibodies. Heparin-induced thrombocytopenia (HIT) is caused by antibodies against heparin–platelet factor 4 complexes that activate platelets and cause thrombosis. HIV infects megakaryocytes and promotes autoantibodies.
Structure
- Marrow: normal or increased megakaryocytes, some large and immature.
- Spleen: normal size, congested sinusoids, prominent follicles and occasional megakaryocytes in sinuses.
- Skin and mucosa: petechiae, ecchymoses; rarely intracranial bleeding.
Step by step
- IgG autoantibodies (or drug-dependent antibodies) bind platelet membrane glycoproteins.
- Fc receptors on splenic macrophages recognize opsonized platelets and remove them.
- Antibodies may also injure megakaryocytes, reducing production.
- In HIT, antibodies bind PF4–heparin complexes on platelets and activate them through Fc receptors.
- Activated platelets release procoagulant microparticles: thrombosis despite low counts.
Immune thrombocytopenias compared
| Type | Who and trigger | Target | Outcome |
|---|---|---|---|
| Chronic ITP | Adult women; primary or with lupus, HIV, CLL | GPIIb/IIIa or GPIb/IX | Chronic, responds to glucocorticoids, splenectomy or other therapy |
| Acute ITP | Children after a viral infection | Platelet glycoproteins | Usually resolves within six months |
| Drug-induced | Quinine, quinidine, vancomycin, GPIIb/IIIa inhibitors | Drug-dependent epitopes | Resolves when the drug is stopped |
| Heparin-induced (type II) | Five to fourteen days of heparin | PF4–heparin complexes | Thrombosis, limb loss risk |
| HIV-associated | HIV infection | GPIIb/IIIa autoantibodies plus infected megakaryocytes | Improves with antiretroviral therapy |
Clinical notes
- Easy bruising, nosebleeds and gum bleeding in a woman with no splenomegaly or lymphadenopathy suggests chronic ITP.
- Splenomegaly in apparent ITP points to another cause, such as lymphoma.
Test yourself
Think of the answer, then tap the question to see it.
Which platelet glycoproteins are targeted in chronic ITP?
GPIIb/IIIa and GPIb/IX.
Why does heparin-induced thrombocytopenia cause thrombosis?
Antibodies to PF4–heparin complexes activate platelets, which release procoagulant material.
Why does splenectomy help in ITP?
The spleen is the main site of removal of antibody-coated platelets and also a source of the autoantibodies.
Elsewhere in DurgiPedia
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Immune thrombocytopenic purpura (ITP): MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026).
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Representative model, for educational purposes only.