Define thrombocytopenia and differentiate between its 4 major causes

• Thrombocytopenia = decreased platelet numbers

  • Normal = 150,000 – 450,000/mm³

  • Spontaneous bleeding if platelet count <>3

• Thrombocytopenic bleeding usually seen with petechiae of skin and mucus membranes

• Most common cause in the face of normal bone marrow is idiopathic thrombocytopenic purpura

• Thrombocytopenia is quite often a sign of early leukemia

• Decreased platelet production

  • Generalized bone marrow disease

    • Aplastic anemia

    • Marrow infiltration (myelophthisic)

  • Selective impairment of platelet production

    • Drug-induced (EtOH, thiazides, cytotoxic drugs, etc)

    • Infections (childhood rubella, HIV)

  • Ineffective megakaryopoiesis

    • Megaloblastic anemias

    • Myelodysplastic syndromes (similar to megaloblastic anemias but they are due to an acquired DNA abnormality)

    • Paroxysmal nocturnal hemoglobinuria

    • Inherited d/o (Wiskott-Aldrich syndrome, hereditary immunodeficiency with thrombocytopenia, eczema, and recurrent infections)

• Decreased platelet survival

  • Immunologic destruction

    • Autoimmune (ITP, SLE)

    • Isoimmune (alloimmune): post-transfusion (because platelets have Ags on them other than ABO) and neonatal

    • Drug-associated (quinine, quinidine, heparin, penicillins, sulfa compounds, thiazides, methyl dopa, heparin)

    • Infections (EBV, HIV, CMV)

  • Increased consumption

    • DIC

    • Thrombotic microangiopathies (TTP, HUS)

    • Vascular abnormalities (giant hemangiomas, arteritis, etc)

    • Microangiopathic hemolysis

• Sequestration (hypersplenism)

• Dilutional thrombocytopenia with massive transfusion (should give 1 platelet transfusion for every 10 units of blood cells)

Category: Medical Subject Notes , Pathology Notes