Platelet abnormalities in myeloproliferative disorders.

A large number of various platelet abnormalities are described in patients with MPD. These abnormalities serve diagnostic purposes only. They appear to have little or no predictive value regarding the clinical manifestations of the patients or the progress of the disease. Those platelet characteristics most consistently reported to be defective include a decrease in the platelet content of serotonin and adenine nucleotides, decreased platelet density, an abnormal ultrastructure characterized by paucity of granules and hypertrophy of the surface connecting canicular system, an altered membrane glycoprotein profile that includes reduced levels of GPIb, and reduced lipoxygenase activity and aggregation response with epinephrine. These abnormalities may originate at the megakaryocyte level. Furthermore, the released abnormal platelets may undergo modification of their functional and biochemical characteristics as a result of episodes of intravascular thrombosis or aging in circulation or as a result of the progression and treatment of the disease, thus creating the paradoxic and often conflicting relationship between the thrombotic and hemorrhagic events and the results of platelet functional tests as observed in this disorder.