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For further information, see CMDT Part 14-04: Increased Platelet Destruction

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 is a diagnosis of exclusion

General Considerations

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

  • 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)

  • Targets of antiplatelet antibodies 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])

Table 14–7.Selected medications causing drug-associated thrombocytopenia.1

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

  • Additional disease-specific findings may be present in persons with secondary immune thrombocytopenia (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, often < 25,000/mcL

  • If 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 not characteristic of immune thrombocytopenia, but patients with ITP often have increased numbers of bone marrow megakaryocytes

  • In the absence of such findings, otherwise asymptomatic patients with unexplained isolated thrombocytopenia of recent onset may be considered to have immune thrombocytopenia

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