ET is a chronic state of thrombocytosis that is neither reactive nor related to CML, MMM, PV, or MDS.
Serum thrombopoietin levels are elevated or normal despite a high PLT count.
This may be secondary to decreased clearance because of reduced TPO-receptor expression in platelets & megakaryocytes (c-Mpl).
Patient not s/p splenectomy
normal ferritin & C-reactive protein (no reactive processes)
Bone marrow excludes MDS, AMM, CML, etc
1. 25% are asymptomatic at presentation
2. Vasomotor symptoms that includes headaches, transient ocular symptoms, transient neurological symptoms, erythromelalgias, distal paresthesias
3. Thrombosis: arterial or venous including CAD, CVA, PE, DVT, hepatic or portal vein thrombosis, digital ischemia.
5. Leukemic conversion in <5%
6. Spontaneous early term abortion up to 45% of the pregnancies in ET.
Age & history of thrombosis are predictors of future thrombotic events
Note that the degree of thrombocytosis or platelet function abnormalities are not predictors of thrombosis.
Note that treatment of patients with ET remains contraversial. Most physicians have favored treating ALL SYMPTOMATIC patients or patients with PLT>1-1.5 million/uL.
Aspirin is effective at reducing symptoms of microvascular occlusion in ET. a single dose of ASA can relieve symptoms of erythromelalgia for a few days. Daily ASA also relieves cerebrovascular symptoms.
---take ASA 75-100 mg po QD
---Hydroxyurea has been shown to reduce the risk of thrombosis in high risk patients from 24% to 4%! Also can try to maintain PLT<400,000.
Lowering Platelet count:
1. Hydroxyurea 15-30 mg/kg/day (rapid onset of action, control of thrmobocytosis in 4-6 weeks)
2. Anagrelide 0.5 mg Qid
This drug appears to work by decreasing megakaryocyte maturation. It has little effect on WBC but can lower RBC in 30% of patients. Need to watch for cardiovascular side effects including CHF & water retention. other side effects include headaches, nausea, or diarrhes.
3. Alpha-interferon 21-35 million units SQ Qweek X 4 weeks then maintenance dose 3 MU QD or 3x/week to keep PLT<600,000.
For symptomatic patients who need emergent lowering of their PLT count. It should be combined with hydroxyurea i.e. 1.5-3.0 grams QD