Immune Thrombocytopenic Purpura

Overview

ITP = thrombocytopenia from anti-platelet antibodies, shortened platelet survival. Two forms — acute and chronic — different enough to be near-separate entities.

Acute ITP

• Post-viral, mainly children
• Mechanism: immune complexes (viral Ag-Ab) stick to platelet surface → platelets destroyed as bystanders during complex clearance
• Self-limited, weeks to 6 months
• ~90% spontaneous recovery

Chronic ITP

• Adults, mainly women 20-40yr
• Mechanism: antiplatelet IgG against platelet GpIIb-IIIa/GpIb-IX → splenic macrophage destruction (like warm AIHA)
• Persistent/relapsing; <10% spontaneous recovery

Clinical features (both)

Petechiae, bruising, mucosal bleeding (epistaxis, gum bleeding, menorrhagia). Chronic: splenomegaly/hepatomegaly possible. Both: NO lymphadenopathy (helps rule out lymphoproliferative cause).

Lab findings

• Platelet count 10,000-50,000/µL
• Smear: large platelets
• Marrow: increased non-lobulated megakaryocytes (compensating, not failing)
• Anti-platelet IgG demonstrable
• Platelet survival <1hr (normal 7-10 days)

Treatment

Acute: supportive (high spontaneous recovery). Chronic: corticosteroids, immunosuppressants, splenectomy for refractory cases.

Clinical relevance

Acute vs chronic isn’t just duration — different mechanism (bystander immune complexes vs true autoantibody), which is why age group, course, and treatment all differ. Increased non-lobulated megakaryocytes = marrow compensating for peripheral loss, not failing — confirms this is a destruction disorder, not a production disorder, which changes the whole workup. No lymphadenopathy despite organomegaly in chronic ITP helps rule out lymphoproliferative disease.

Overview

Immune (idiopathic) thrombocytopenic purpura (ITP) is thrombocytopenia caused by anti-platelet antibodies shortening platelet survival. It presents in two clinically distinct forms — acute and chronic — that differ enough in age group, mechanism, course, and treatment response to be considered almost separate entities sharing a common antibody-mediated destructive process.

Acute ITP

• Typically follows a viral infection, most often in children.
• Mechanism: immune complexes (viral antigen–antibody) adsorb onto the platelet surface, and platelets are then destroyed as “innocent bystanders” during clearance of these complexes — rather than the antibody being directed against a platelet antigen itself.
• Course: self-limited, typically resolving within weeks to 6 months.
• Spontaneous recovery in roughly 90% of cases.

Chronic ITP

• Occurs mainly in adults, with a striking predominance in women aged 20–40 years.
• Mechanism: antiplatelet IgG autoantibodies directed against specific platelet membrane glycoproteins, chiefly GpIIb-IIIa and GpIb-IX. Antibody-coated platelets are recognised and destroyed by splenic macrophages (splenic destruction), analogous to the extravascular haemolysis mechanism in warm-antibody autoimmune haemolytic anaemia.
• Course: persistent, relapsing; spontaneous recovery in under 10%.

Clinical Features (Both Forms)

• Petechiae and easy bruising (ecchymoses).
• Mucosal bleeding — epistaxis, gum bleeding, menorrhagia.
• Splenomegaly and hepatomegaly may be present in chronic ITP (from the sustained work of platelet clearance); lymphadenopathy is absent in both forms — a feature that helps exclude a lymphoproliferative cause for the thrombocytopenia.

Laboratory Findings

• Platelet count: 10,000–50,000/µL.
• Peripheral smear: large platelets (megathrombocytes), reflecting increased marrow output in response to peripheral destruction.
• Bone marrow: increased numbers of non-lobulated (immature-appearing) megakaryocytes — the marrow is compensating for peripheral platelet loss, not failing to produce platelets.
• Anti-platelet IgG: demonstrable on the platelet surface or in serum.
• Platelet survival: markedly reduced, under 1 hour (normal 7–10 days).

Treatment

• Acute ITP: largely supportive, given the high rate of spontaneous recovery.
• Chronic ITP: corticosteroids, immunosuppressants, and splenectomy (removing the principal site of antibody-mediated platelet destruction) for refractory cases.

Clinical Relevance

• The acute-versus-chronic distinction is not just a matter of duration — it reflects two different immunological mechanisms (bystander immune-complex adsorption in acute ITP versus a true autoantibody against platelet glycoproteins in chronic ITP), which is why their age distribution, natural history, and treatment approach differ so much.
• Increased, non-lobulated megakaryocytes on marrow examination is the finding that correctly identifies ITP as a peripheral destruction disorder rather than a marrow production failure — a distinction that changes the entire differential and management approach for thrombocytopenia.
• The absence of lymphadenopathy in ITP, despite the presence of splenomegaly/hepatomegaly in the chronic form, is a genuinely useful discriminator against lymphoproliferative disorders that can also present with thrombocytopenia and organomegaly.

Diagram 1: Chronic ITP — Splenic Destruction Mechanism

Draw a single vertical chain of four boxes, top to bottom.

1. Anti-platelet IgG — targets GpIIb-IIIa/GpIb-IX.
2. Antibody-coated platelet — circulates, marked for clearance.
3. Splenic macrophage recognition — Fc-receptor mediated binding and phagocytosis.
4. Extravascular platelet destruction — platelet survival <1hr (normal 7-10 days), thrombocytopenia.

Labels required

• Name the specific glycoprotein targets (GpIIb-IIIa, GpIb-IX) rather than a generic “platelet antigen” — these are the actual epitopes named in sources and distinguish this from a nonspecific process.
• The destruction site must be labelled extravascular/splenic — this is the same category of destruction as warm-antibody AIHA, worth noting as a parallel when comparing the two topics.

Errors commonly made

• Confusing this chronic-ITP mechanism (true autoantibody against a platelet antigen) with the acute-ITP mechanism (bystander destruction of platelets carrying adsorbed immune complexes) — these are genuinely different processes, not the same mechanism at two ages.
• Treating ITP as an intravascular/complement-mediated destruction process — it is extravascular, macrophage/Fc-receptor mediated, same category as warm AIHA, not cold AIHA or intravascular haemolysis mechanisms.

Short Essays (2)

Short Answers (1)

Multiple Choice Questions (1)