Up to 50% of patients present with
microvascular occlusions (e.g., fingers and toes with risk of gangrene if
left untreated, priapism), whereas major vessel occlusions (e.g., coronary,
renal and femoral arteries, or hepatic-vein thrombosis [Budd-Chiari
Syndrome], portal vein, splenic, or femoral vein thrombosis) are less
common. Cerebrovascular infarction, transient ischemic attacks, and
myocardial infarction, although common in elderly patients, are less common
in young patients. Pulmonary embolism is a common finding and may result in
chronic pulmonary artery hypertension. Hemorrhage can be a presenting
feature, is generally not severe, and often is associated with platelet
counts greater than 1000 × 109/liter, with the gastrointestinal
tract (duodenum) the most common site of bleeding. Other sites of bleeding
may include the urogenital tract, skin, gums, eyes, and central nervous
system. Results of screening tests of coagulation usually are normal, but
bleeding time may be prolonged. Splenomegaly and hepatomegaly (less common)
are present in a significant number of patients. B symptoms (weight loss,
fever, sweating) but also pruritus have been described in up to one third of
patients. The risk of transformation into an acute leukemia reported in the
literature varies between 2% and 20%. Death is usually the result of
thromboembolic complications. Ten-year survival may be as high as 80%.
Aspirin is the mainstay of management against recurrent thrombotic events
(and places these patients at high risk for bleeding). Hydroxyurea,
busulphan, and pipobroman have been used to lower very high platelet counts,
although they may increase the rate of conversion to acute leukemia
(leukemogenicity). This has suggested use of a conservative approach to
management in younger patients. Anagrelide (an imidazoquinazoline compound
that not only inhibits platelet aggregation but also results in suppression
of megakaryocyte maturation with a decreased platelet count) has been used
successfully to reduce the platelet count, while α-interferon
currently is being investigated for use in ET. Plateletpheresis is used for
patients with acute cerebrovascular complications or digital ischemia, for
which rapid reduction of the platelet count is required.