Immune thrombocytopaenia

Immune thrombocytopaenia (ITP), also called immune thrombocytopaenic purpura, is an immune-mediated cause of thrombocytopaenia. It is caused by the formation of autoantibodies against thrombocytes and is relatively common. Other cell lines are unaffected.

It usually either affects children <5 or older adults >55 years, but the disorder is a bit different in the two populations. In children, it’s typically acute and self-limiting. In adults, it’s typically chronic and persisting.

Classification

Primary immune thrombocytopenia: autoimmune disorder characterized by isolated thrombocytopenia with no known cause. In other words, idiopathic. Often follows a viral infection.

Secondary immune thrombocytopenia: Isolated thrombocytopenia due to an autoimmune hematologic disorder with a known trigger. It is associated with lymphoma, leukaemia (especially CLL), SLE, HIV, HCV, and drug reactions.

Persistent ITP means that it has lasted 3 – 12 months, while chronic ITP means that it has lasted for more than 12 months.

Pathophysiology

IgG antiplatelet antibodies bind to the surface proteins on platelets. They get sequestrated by the spleen and liver, leading to a decreased platelet count. This will lead to an increased megakaryocyte production, and therefore platelet production on the bone marrow.

Clinical features

Many patients are asymptomatic. Those with symptoms usually present with minor bleedings such as petechias, purpuras and epistaxis. Severe bleedings are rarely seen, and examples of this are GI bleedings or intracranial haemorrhage.

Spontaneous bleedings usually don’t occur unless the platelet level is <30 G/L, and serious bleeding usually don’t occur unless it’s <20.

Diagnosis and evaluation

It’s a diagnosis of exclusion, so we must exclude other causes of thrombocytopaenia like drug side effects, infections, autoimmune disorders, lymphoproliferative disorders, etc. In ITP, there is isolated thrombocytopaenia, so the other cell lines are normal. The platelet count can be very low, even < 10 G/L (normally 140 – 440).

Platelets have normal morphology on blood smear. Bone marrow biopsy can be performed in case of uncertain cases, which will show increased number of megakaryocytes. Patients should be tested for HIV and HCV. Testing for antiplatelet antibodies is not indicated.

Treatment

For children with no symptoms or mild mucocutaneous bleedings, observation is enough as it usually resolves by itself. This applies to adults with no symptoms or minor bleedings with platelet counts above 30 G/L as well. They should be advised to not do contact sports as it is a bleeding risk.

If spontaneous bleedings occur or platelets are <30, pharmacological treatment is indicated. First-line medical therapy consists of corticosteroids or IVIG. Second line is thrombopoietin receptor agonists such as romiplostim, or splenectomy.