Immune Thrombocytopaenia (ITP)
Important clarification in terminology:
- The term idiopathic thrombocytopaenic purpura is now outdated
- ITP is currently defined as immune thrombocytopaenia, reflecting its underlying autoimmune mechanism rather than an unknown (“idiopathic”) cause
ITP is therefore classified as:
- Primary ITP: no identifiable underlying cause
- Secondary ITP: associated with an underlying condition
Definition
ITP is an acquired immune-mediated disorder characterised by isolated thrombocytopaenia, and is a diagnosis of exclusion (i.e. no alternative non-immune cause identified).
Epidemiology
ITP affects both children and adults [Ref]
- Children: usually acute and self-limiting
- Adults: more likely to develop chronic ITP
Aetiology
ITP may be classified as primary or secondary, and is a diagnosis of exclusion of non-immune causes of thrombocytopaenia. [Ref]
| Primary ITP | No identifiable underlying cause – most common form |
| Secondary ITP | Associated with an underlying condition, including:
|
The exact pathophysiology is complex and incompletely understood. [Ref]
As a general concept, antibody-coated platelets are prematurely destroyed in the spleen and/or liver. [Ref]
Clinical Features
Clinical features of ITP are highly variable and depend on the degree of thrombocytopaenia [Ref1][Ref2]
- Many patients are asymptomatic and are diagnosed incidentally
- If symptomatic, ITP presents with isolated thrombocytopaenia
- Classic mucocutaneous bleeding (e.g. petechiae, epistaxis, gum bleeding, menorrhagia)
- Severe haemorrhage (e.g. GI bleeding, intracranial haemorrhage) is less common and usually happens if platelet counts are very low
- The patient is usually otherwise well with normal examination findings apart from bleeding signs (i.e. no splenomegaly, no lymphadenopathy etc.)
Differential Diagnosis
ITP is a diagnosis of exclusion, therefore other causes of thrombocytopenia must be considered: [Ref]
| Differential diagnosis | Key suggestive features |
|---|---|
| TTP |
See the Thrombotic Thrombocytopaenic Purpura (TTP) article for more information |
| Heparin-induced thrombocytopaenia |
|
| Aplastic anaemia |
|
| Acute leukaemias |
See the Acute Leukaemia article for more information |
| Myelodysplastic syndrome |
|
Investigation and Diagnosis
ITP is a diagnosis of exclusion, characterised by: [Ref]
- Isolated thrombocytopenia (platelet count <100 × 10⁹/L) – low platelets with otherwise normal blood counts and blood film
- With no alternative cause identified (see the differential diagnosis section above)
Initial tests to exclude alternative causes:
- FBC → to confirm isolated thrombocytopaenia
- Peripheral blood film → exclude TTP (schistocytes) and leukaemias (blasts)
- Coagulation screen → exclude DIC
- Viral screen (e.g. HIV, hepatitis B and C) → identify secondary causes
- Autoimmune screen → identify secondary causes
Management
Management depends on bleeding severity, platelet count, and individual risk factors.
Do not routinely offer prophylactic platelet transfusions in ITP.
Platelet transfusions should only be used in active / significant bleeding and must be given with immunosuppression, as transfused platelets are rapidly destroyed.
Acute Management
Acute management is indicated in: [Ref]
- Active significant or life-threatening bleeding, or
- Very low platelet count (<10 x 109/L)
Acute management components: [Ref]
| Immediate measure | Stop any anticoagulants / antiplatelets if possible |
| Core treatment |
|
| Adjuncts |
|
Long-Term Management
Active observation (no treatment) is appropriate in patients who are asymptomatic or have only mild mucocutaneous bleeding. [Ref]
In children, ITP is often acute and self-limiting → observation under the supervision of a haematologist is often appropriate. [Ref]
Treatment is generally initiated to prevent future bleeding if: [Ref]
- Platelet count <20-30 x 109/L – common criteria
- High-risk features (e.g. >65 y/o, history of bleeding, concurrent use of anticoagulants / antiplatelets, renal impairment)
Choice of treatment: [Ref]
- 1st line: oral corticosteroids (usually prednisolone or dexamethasone)
- Further therapy:
- Thrombopoietin receptor agonists (e.g. avatrombopag, eltrombopag, romiplostim)
- Fostamatinib
- Rituximab
- Splenectomy – to be considered if refractory to drugs (most effective treatment)