Q 2 Bleeding Disorders: Platelet Disorders

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Study Notes

Thrombocytopenia is a reduction in platelet number, which can result from: • Decreased platelet production • Increased sequestration of platelets in the spleen • Destruction of platelets by antibodies • Depletion of platelets due to thrombi • Dilution of blood through multiple transfusions • Decreased platelet survival

Some drugs, such as aspirin, atorvastatin, and some antibiotics, can cause drug-induced immune thrombocytopenia
These drugs induce an antigen-antibody response and formation of immune complexes, leading to platelet destruction by complement-mediated lysis
Drug-associated thrombocytopenia is characterized by: • Rapid fall in platelet count within 2 to 3 days of resuming a drug or 7 or more days after starting a drug for the first time • Rapid rise in platelet count after the drug is discontinued

HIT is associated with the anticoagulant drug heparin
50% of people treated with heparin develop a mild, transient thrombocytopenia within 2 to 5 days of starting the drug
Approximately 1% to 5% of people treated with heparin experience life-threatening thromboembolic events 1 to 2 weeks after the start of therapy
HIT is caused by an immune reaction directed against a complex of heparin and platelet factor 4
Treatment of HIT requires the immediate discontinuation of heparin therapy

ITP is an isolated thrombocytopenia with a platelet count of less than 100,000 mL
Characterized by: • Purpuric rash • Normal white blood cells • Normal hemoglobin
ITP results in platelet antibody formation and excess destruction of platelets
Primary ITP: • Affects both children and adults • Highest incidence in people older than 60 years • Classified as: • Newly diagnosed (from diagnosis until 3 months) • Persistent (from diagnosis until 3 to 12 months) • Chronic (from diagnosis until >12 months)
Secondary ITP: • Associated with autoimmune disorders and chronic infections such as: • Helicobacter pylori • Hepatitis C virus • Epstein-Barr virus • HIV • Clinical manifestations include: • A history of bruising, bleeding from the gums, epistaxis, melena, and abnormal menstrual bleeding • Splenic enlargement may occur • Condition may be discovered incidentally or as a result of signs of bleeding

Familial form: • Autosomal recessive inheritance • Rare, appearing in infancy and early childhood • Symptoms occur regularly and exacerbate with stress
Acquired form: • Not inherited • More common, occurring in late childhood or into adulthood • May be a single occurrence or many occurrences over time