Chapter 8-6: Idiopathic Thrombocytopenia Purpura (ITP)

TEXTBOOK PRESENTATION

The classic presentation is gum bleeding or petechiae in a previously healthy person not exposed to medications that can cause thrombocytopenia. The platelet count is low, with large platelets seen on peripheral blood smear; other cell lines are normal. Physical exam, other than the minor bleeding, is normal.

DISEASE HIGHLIGHTS

1. ITP is an autoimmune disorder primarily of young women. This is the demographic group that commonly suffers from other autoimmune disorders such as SLE or thyroid disease.

2. A better term might be autoimmune thrombocytopenic purpura, since some cases are not idiopathic but are secondary to other conditions, such as lymphoproliferative disorders, collagen vascular disorders (eg, SLE), or infectious disorders (eg, chronic hepatitis or HIV infection).

3. The prevalence is approximately 100 cases per million persons.

EVIDENCE-BASED DIAGNOSIS

1. ITP is a clinical diagnosis.

2. A bone marrow examination is not required for diagnosis.

   1. If performed, it would likely show normal or increased megakaryocytes, indicating adequate platelet production and suggesting the thrombocytopenia is due to peripheral destruction of platelets in the reticuloendothelial system.

   2. A bone marrow examination should be done when the presentation is atypical, for example:

      1. Patient has splenomegaly or significant lymphadenopathy or other cytopenias

      2. The patient is older.

3. Serum antiplatelet antibody tests are about 50–60% sensitive and not sufficiently specific to make the diagnosis of ITP.

   1. They are not considered sufficiently reliable for general use in diagnosing ITP.

   2. If there is serious consideration of a drug-induced cause of immune thrombocytopenia, it may be possible to demonstrate drug-related antiplatelet antibodies in reference laboratories.

4. A successful clinical trial of corticosteroid therapy may also serve as strong evidence of the correct diagnosis of ITP.

5. Serologic studies are indicated if SLE, hepatitis C, or HIV infection is suspected.

TREATMENT

1. High-dose corticosteroid, such as prednisone or dexamethasone, is the initial treatment for all patients.

2. Patients who do not respond to corticosteroids or whose thrombocytopenia recurs when the corticosteroids are stopped may undergo splenectomy, which removes a site of antibody production as well as a site of reticuloendothelial system destruction of antibody-coated platelets.

3. In refractory cases, other immunosuppressants may be used, such as rituximab, azathioprine, or cyclophosphamide.

4. Thrombopoietin analogues such as romiplostim and eltrombopag have become more widely used for treatment of refractory cases of ITP.