Idiopathic thrombocytopenic purpura (ITP)

Overview

•Type 2 hypersensitivity - defective B cells produce IgG autoantibodies against platelet glycoproteins (GPIIb/IIIa) → antibody-coated platelets destroyed by splenic macrophages → isolated thrombocytopenia

•Children: peak age 2-5 years, often preceded by viral illness 1-3 weeks prior; typically self-limiting

•Adults: most common in women aged 20-40; more chronic course; secondary causes include SLE, HIV, hepatitis C

Presentation

•Petechiae - pinpoint non-blanching spots (<3 mm)

•Purpura - larger non-blanching red-purple macules (3-10 mm)

•Easy bruising, epistaxis, gingival bleeding, menorrhagia

•Patient is otherwise well - no fever, no organomegaly, no systemic upset

•Splenomegaly is absent in primary ITP - if present, investigate for alternative diagnosis (bone marrow biopsy indicated)

🚨

Well child with petechiae after viral illness = ITP until proven otherwise. Unwell child with petechiae and fever = meningococcal sepsis until proven otherwise - give benzylpenicillin empirically without delay.

Investigations

•FBC - isolated thrombocytopenia; Hb and WBC normal

•Blood film - normal red cell morphology, no schistocytes, may show large platelets

•Coagulation screen (PT, APTT, fibrinogen) - normal in ITP

•Autoimmune screen (ANA, anti-dsDNA) - exclude secondary ITP/SLE

•Viral serology (HIV, hepatitis B/C, EBV) - exclude viral secondary cause

•Bone marrow biopsy - NOT routine; only if atypical features: splenomegaly, lymphadenopathy, bone pain, unexplained anaemia or leukopenia

🎯

Schistocytes on film = think TTP or DIC, not ITP. Blasts or leukoerythroblastic picture = think haematological malignancy (e.g. ALL). Normal film with isolated thrombocytopenia = ITP.

Management

•Observation - well patients, mild bleeding, platelets >30 x 10^9/L; avoid NSAIDs/antiplatelets; most paediatric cases resolve within 6-12 months

•First-line (treatment threshold): platelets <30 x 10^9/L or significant bleeding

•Prednisolone (1-2 mg/kg/day, tapered over 2-4 weeks) - suppresses Fc receptor expression on splenic macrophages; first-line pharmacological treatment

•IVIG (0.8-1 g/kg) - saturates Fc receptors, rapid platelet rise; preferred pre-surgery, severe bleeding, or in children; effect is temporary

🥈 Second-line

•romiplostim / eltrombopag (TPO-RAs) - stimulate megakaryocyte proliferation; for relapsed/refractory chronic ITP

•rituximab (anti-CD20) - depletes autoreactive B cells; chronic refractory ITP

🥉 Third-line

•splenectomy - removes primary site of destruction; ~60-70% durable remission; requires pre-op vaccination against encapsulated organisms (pneumococcus, Hib, meningococcus)

Prognosis

•Children: ~70-80% resolve spontaneously within 6 months; <1% develop intracranial haemorrhage

•Adults: more likely chronic/relapsing-remitting; secondary ITP improves with treatment of underlying cause

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Intracranial haemorrhage is rare (<1%) but life-threatening - most likely with platelets <10 x 10^9/L. Treat as emergency: IVIG + high-dose steroids + platelet transfusion.

Differentiating ITP from Key Mimics