PLATELET DISORDERS

Causes of Thrombocytopenia

Idiopathic Thrombocytopenic Purpura

Thrombotic Thrombocytopenic Purpura

• Platelet lifetime avg. 7d
• Normal platelet count = 150-400k/uL
• Platelet count < 70 gives elevated bleeding time
• Serious spontaneous bleeding rare with platelet count > 20
• Excessive bleeding with trauma or surgery rare with platelet count > 50

Common wisdom has it that initial bleeding due to platelet disorders is usually from mucous membranes rather than bruising of the skin or hemarthrosis

Essential thrombocythemia

• Must be differentiated from reactive and neoplastic causes of thrombocytosis (check CRP, ESR, fibrinogen, bone marrow Bx)
• Associated with vasomotor sx e.g. headaches and paresthesias
• Uncommonly associated with thrombocytosis and/or hemorrhage
• Rarely, may "transform" into acute leukemia or myelofibrosis
• Usually treated with hydroxyurea
• In a prospective study of 332 pts with essential thrombocythemia, over median 14y f/u, 10y incidence of a thrombotic event was 42% and for a hemorrhagic event, 15%. Incidence of transformation to leukemia was 1% at 10y, 8% at 20y, and 24% at 30y. Treatment with cytoreductive drugs was not associated with incidence of myeloid transformation (Mayo Clin. Proc. 81:159, 2006--JW)

Eltrombopag is a (as of 2007) investigational agent that is orally active and acts as an agonist at thrombopoietin receptors and may hold promise in treating various forms of thrombocytopenia.