Immune Thrombocytopenia

Key Features

Essentials of Diagnosis

• Isolated thrombocytopenia (rule out pseudothrombocytopenia by review of peripheral smear)

• Assess for any new causative medications and HIV and hepatitis B and C infections

• Immune thrombocytopenia (ITP) is a diagnosis of exclusion

General Considerations

• ITP is an autoimmune condition in which pathogenic antibodies bind platelets, accelerating their clearance from circulation

• Growing evidence suggests additional pathophysiologic mechanisms, including a role for T cells

• The disorder is primary (idiopathic) in most adult patients, although it can be secondary, ie associated with

  • Connective tissue disease (such as lupus)

  • Lymphoproliferative disease (such as lymphoma)

  • Medications (see Table 14–7)

  • Infections (such as HIV, hepatitis C, Epstein-Barr, and Zika virus infections)

  • Can be exacerbated by SARS-CoV-2 vaccination

• Antiplatelet antibody targets include glycoproteins IIb/IIIa and Ib/IX on the platelet membrane, although antibodies are demonstrable in only two-thirds of patients

• In addition to production of antiplatelet antibodies, HIV and hepatitis C virus may lead to thrombocytopenia through additional mechanisms (for instance, by direct suppression of platelet production [HIV] and cirrhosis-related decreased thrombopoietin production and secondary splenomegaly [hepatitis C virus])

Clinical Findings

Symptoms and Signs

• Mucocutaneous bleeding may be present, depending on the platelet count

• Clinically relevant spontaneous bruising, epistaxis, gingival bleeding, or other types of hemorrhage generally do not occur until the platelet count has fallen below 10,000–20,000/mcL (10–20 × 10⁹/L)

• Additional disease-specific findings may be present in persons with secondary ITP (such as due to collagen vascular disease, HIV or HCV infection, or lymphoproliferative malignancy)

Differential Diagnosis

• Thrombotic thrombocytopenic purpura

• Acute leukemia

• Myelodysplastic syndrome

• Disseminated intravascular coagulation

• Early aplastic anemia

• Drug toxicity (eg, heparin, sulfonamides, thiazides, quinine)

• Alcohol abuse

• Hypersplenism

• Systemic lupus erythematosus

Diagnosis

Laboratory Tests

• Isolated thrombocytopenia with platelet count < 100,000/mcL (100 × 10⁹/L), often < 25,000/mcL (25 × 10⁹/L)

• If substantial bleeding has occurred, anemia may also be present

• Serologic testing to exclude hepatitis virus B and C and HIV infections

• Megakaryocyte morphologic abnormalities and hypocellularity or hypercellularity are ...