Diagnostic criteria and prognosis in polycythemia vera and essential thrombocythemia.

Polycythemia vera (PV) and essential thrombocythemia (ET) are two myeloproliferative disorders (MPDs) that result from an acquired mutation of a single hematopoietic stem cell that gives the progeny of the stem cell a growth advantage over their normal counterparts. The incidence of both diseases appears to be similar. From time to time, PV has an atypical presentation making it difficult to differentiate from ET and other MPDs. Identification of a patient as having PV or ET generally follows the observation of elevated hematocrit or elevated platelet count. Thrombotic complications are the major cause of morbidity and mortality in both groups of patients. In PV, the frequencies of venous and arterial thrombosis are about equal, whereas venous thrombosis is less common in ET. Accurate diagnosis of these disorders is essential for proper treatment. The prognosis for untreated, asymptomatic ET patients is generally good, but quite poor for untreated PV patients. Proper treatments have been shown to reduce complications and significantly extend the life span for both groups of patients.