Define thrombocytopenia and differentiate between its 4 major causes

on 9.2.09 with 0 comments

  • 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



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