Essential thrombocythemia (ET) is a clonal myeloproliferative neoplasm characterized by persistent platelet count ≥450 × 10⁹/L with excessive megakaryocyte proliferation, carrying increased risks of arterial thrombosis (11%), venous thrombosis (7%), and hemorrhagic complications (8%). [1] The US annual incidence is approximately 1.5/100,000 persons, with a median age at diagnosis of 59 years. [1] Median overall survival exceeds 35 years in those diagnosed at age ≤40. [1]
1. History
- Key HPI questions: Headaches, lightheadedness, visual disturbances (blurred vision, scotomata), acral paresthesias, burning/tingling in fingers and toes, erythromelalgia (pain with erythema/warmth in distal extremities) [1-2]
- Symptom characterization: Microcirculatory symptoms occur in ~29% of adults; >50% are asymptomatic and diagnosed incidentally on CBC [1]
- Timing/triggers: Symptoms may be chronic and insidious; erythromelalgia often triggered by warmth or exercise
- Associated symptoms: Easy bruising, mucocutaneous bleeding (nosebleeds, gum bleeding, GI bleeding), early satiety or left upper quadrant fullness (splenomegaly) [1-2]
- Important negatives: Absence of fever, weight loss, and drenching night sweats helps distinguish from more aggressive myeloproliferative neoplasms or myelofibrosis [3]
2. Alarm Features
- Acute stroke, TIA, or acute coronary syndrome — arterial thrombosis is the most common major vascular event [4-5]
- Splanchnic vein thrombosis (portal, mesenteric, hepatic, splenic) or cerebral venous sinus thrombosis — should prompt MPN workup even in young patients [1]
- Pulmonary embolism or DVT [2]
- Severe or unexplained hemorrhage, especially GI bleeding — may indicate acquired von Willebrand syndrome (VWS), particularly with platelet counts >1,000 × 10⁹/L [3-4]
- Constitutional symptoms (>10% weight loss in 6 months, night sweats, unexplained fever >37.5°C) — suggest transformation to post-ET myelofibrosis [3]
- Rapidly enlarging spleen, new anemia, leukoerythroblastic blood smear — red flags for fibrotic transformation [3]
- Blast cells on peripheral smear — concern for accelerated/blast phase MPN [3]
3. Medications
- Low-dose aspirin (81–100 mg/day): Cornerstone of thromboprophylaxis for most patients except very-low-risk triple-negative patients without cardiovascular risk factors. Twice-daily aspirin may be considered for refractory symptoms or cardiovascular risk factors. [1][3][5]
- Hydroxyurea: First-line cytoreductive agent for high-risk ET. Dose adjusted to keep platelet count controlled. [1][3]
- Peginterferon alfa-2a: Preferred for younger patients, pregnant patients, or those deferring hydroxyurea. [3]
- Ropeginterferon alfa-2b-njft: Category 1 preferred second-line agent for inadequate/loss of response. [3]
- Anagrelide: Other recommended option; moved to "useful in certain circumstances" in second-line per NCCN v1.2026. [3]
- Ruxolitinib: Useful in certain circumstances for refractory disease. [3]
- Contraindications/cautions:
- Aspirin should be withheld in patients with acquired VWS (VWF activity <30%) or active bleeding [3-4]
- Aspirin + anticoagulation increases bleeding risk — individualize [3]
- Hydroxyurea is teratogenic — avoid in pregnancy [3]
- No treatment has been shown to increase survival or prevent progression to myelofibrosis or leukemia [1][5]
4. Diet
- No specific dietary triggers or restrictions unique to ET
- Adequate hydration is important to reduce blood viscosity and thrombotic risk
- Iron supplementation should be guided by iron studies — iron deficiency itself can cause reactive thrombocytosis and must be excluded [1][5]
- Long-term cardiovascular risk factor management includes dietary modifications for hypertension, diabetes, and hyperlipidemia [1]
5. Review of Systems
- Neurologic: Headaches, dizziness, visual changes, TIA symptoms, paresthesias [1]
- Vascular: Erythromelalgia, limb pain/swelling (DVT), chest pain/dyspnea (PE), abdominal pain (splanchnic thrombosis) [2][5]
- Hematologic: Easy bruising, epistaxis, gum bleeding, GI bleeding, menorrhagia [4]
- Constitutional: Fatigue, night sweats, weight loss, fever (suggest disease progression) [3]
- GI: Early satiety, LUQ fullness (splenomegaly), abdominal pain [1]
- Skin: Pruritus (especially aquagenic), livedo reticularis [2]
6. Collateral History and Family History
- Prior CBC results to establish chronicity and trajectory of platelet count
- History of thrombotic or hemorrhagic events in the patient or family
- Family history of myeloproliferative neoplasms (rare familial clustering exists) [2]
- Medication history including antiplatelet/anticoagulant use
- Transfusion history [3]
- Social context: smoking status (modifiable cardiovascular risk factor) [1]
7. Risk Factors
For thrombosis (revised IPSET-Thrombosis model): [1][3-4]
- Age >60 years
- Prior history of thrombosis (strongest predictor)
- JAK2 V617F mutation (associated with higher arterial and venous thrombosis rates)
- Cardiovascular risk factors: Hypertension, diabetes, hyperlipidemia, tobacco use
For hemorrhage: [4]
- Extreme thrombocytosis (platelet count >1,000–1,500 × 10⁹/L) — associated with acquired VWS
- Prior hemorrhage
- Aspirin use in setting of acquired VWS
For disease transformation: [1]
- ~10% develop post-ET myelofibrosis at median 8.5 years
- ~3% develop acute myeloid leukemia
8. Differential Diagnosis
- Reactive (secondary) thrombocytosis (85–90% of all thrombocytosis) — infection, inflammation (RA, SLE), iron deficiency, post-splenectomy, solid tumors, recovery from alcohol/chemotherapy [1]
- Polycythemia vera — may present with thrombocytosis; distinguished by elevated hemoglobin/hematocrit and JAK2 exon 12 mutations [1]
- Primary myelofibrosis (prefibrotic) — can mimic ET closely; distinguished by bone marrow morphology (atypical megakaryocytes, reticulin fibrosis) [1][3]
- Chronic myeloid leukemia — must exclude BCR::ABL1 fusion in all cases [3]
- Myelodysplastic/myeloproliferative overlap syndromes [1]
- Systemic mastocytosis [3]
9. Past Medical History
- Prior thrombotic events (stroke, MI, DVT, PE, splanchnic vein thrombosis) — critical for risk stratification [4]
- Prior hemorrhagic events
- Cardiovascular disease and risk factors (HTN, DM, hyperlipidemia)
- Splenectomy (causes reactive thrombocytosis)
- Autoimmune/inflammatory conditions
- Prior malignancy
- Surgical history (perioperative thrombotic and bleeding risk is elevated in MPN) [3]
10. Physical Exam
- Vital signs: Generally normal; hypertension should be documented as a cardiovascular risk factor
- Spleen: Palpable splenomegaly in ~12% of adults at diagnosis [1][5]
- Skin: Erythromelalgia (erythema, warmth, pain in distal extremities), livedo reticularis, petechiae, ecchymoses [2]
- Neurologic: Focal deficits (if thrombotic event), visual field deficits
- Extremities: Signs of DVT (unilateral leg swelling, tenderness), digital ischemia
- Abdominal: Hepatomegaly (less common), tenderness if splanchnic thrombosis
11. Lab Studies
- CBC with differential and peripheral blood smear — persistent platelet count ≥450 × 10⁹/L; evaluate for leukoerythroblastosis, abnormal WBC/RBC morphology [3][5]
- CMP with uric acid, LDH, LFTs — elevated LDH may suggest disease progression [3]
- CRP — to help exclude reactive causes [5]
- Iron studies with ferritin — exclude iron deficiency as cause of reactive thrombocytosis [3][5]
- Serum EPO level [3]
- Molecular testing: JAK2 V617F first; if negative, CALR and MPL mutations [1][3][5]
- BCR::ABL1 FISH or RT-PCR — mandatory to exclude CML [3]
- Von Willebrand factor antigen and activity — if platelet count >1,000 × 10⁹/L, unexplained bleeding, or pre-surgical evaluation [3-4]
- Bone marrow aspirate and biopsy with reticulin/trichrome stain and cytogenetics — required for definitive diagnosis [3]
12. Imaging
- Abdominal ultrasound or CT — to assess spleen size if not palpable, evaluate for splanchnic vein thrombosis
- CT angiography or MRI/MRV — if splanchnic, cerebral, or other unusual-site thrombosis is suspected [1]
- Routine imaging is not required for diagnosis; bone marrow biopsy is the gold standard morphologic study [3]
13. Special Tests
- Revised IPSET-Thrombosis score — risk stratifies into very-low, low, intermediate, and high risk based on age, JAK2 status, thrombosis history, and cardiovascular risk factors [3-5]
- MPN Symptom Assessment Form Total Symptom Score (MPN-SAF TSS) — standardized symptom burden assessment recommended by NCCN [3]
- Next-generation sequencing (NGS) multigene panel — useful for establishing clonality (especially in triple-negative cases) and prognostic risk stratification [3]
- Bone marrow cytogenetics — karyotyping for prognostic and diagnostic purposes [3]
- Acquired VWS testing — VWF antigen, VWF activity, ristocetin cofactor; expanded panel with factor VIII and VWF multimers in select cases [3]
14. ECG
- Indicated if: Chest pain, dyspnea, or suspicion of acute coronary syndrome (arterial thrombosis is a major complication) [5]
- Findings: ST-segment changes or evidence of ischemia/infarction in the setting of coronary artery thrombosis
- No ET-specific ECG pattern, but baseline ECG is reasonable given elevated cardiovascular risk
15. Assessment
- ET is a chronic, indolent myeloproliferative neoplasm with near-normal life expectancy in younger patients (median survival >35 years if diagnosed at age ≤40) [1]
- The primary clinical burden is vascular events — both thrombotic and hemorrhagic [1]
- 50% of patients are asymptomatic at diagnosis [1]
- Atypical presentations include splanchnic vein thrombosis or cerebral venous thrombosis in young patients, which should always prompt MPN screening [1]
- Complications to consider:
- Transformation to post-ET myelofibrosis (~10% at ~8.5 years) [1]
- Transformation to acute myeloid leukemia (~3%) [1]
- Acquired von Willebrand syndrome with extreme thrombocytosis [4]
The following NCCN algorithm illustrates the risk stratification and treatment approach:
16. Treatment Plan
Risk-stratified approach per NCCN and ELN guidelines: [3-5]
All patients
Very-low-risk (age ≤60, no JAK2, no prior thrombosis)
- Aspirin 81–100 mg/day only if vasomotor/microvascular symptoms present
- Triple-negative patients without cardiovascular risk factors may be observed without treatment [4-5]
Low-risk (age ≤60, JAK2+, no prior thrombosis) and Intermediate-risk (age >60, no JAK2, no prior thrombosis):
- Aspirin 81–100 mg/day [3]
- Monitor; cytoreductive therapy if new thrombosis, progressive symptoms, splenomegaly, or progressive thrombocytosis/leukocytosis [3]
High-risk (prior thrombosis at any age; or age >60 with JAK2+):
- Aspirin 81–100 mg/day + cytoreductive therapy [3]
- Preferred first-line: Hydroxyurea (or clinical trial) [3]
- Other recommended: Peginterferon alfa-2a (especially younger/pregnant patients) or anagrelide [3]
- Second-line (inadequate/loss of response): Ropeginterferon alfa-2b-njft (category 1 preferred), hydroxyurea if not previously used, or peginterferon alfa-2a if not previously used [3]
Acute thrombosis
- Anticoagulation per ACCP guidelines (LMWH, DOAC, or warfarin) [3]
- Initiate or intensify cytoreductive therapy [3]
Emergent situations
Pregnancy
17. Disposition
- Admission criteria:
- Acute thrombotic event (stroke, MI, PE, splanchnic vein thrombosis)
- Severe hemorrhage
- Extreme thrombocytosis with neurologic symptoms requiring emergent plateletpheresis [3]
- Outpatient management: The vast majority of ET patients are managed entirely as outpatients
- Observation: Asymptomatic very-low-risk patients may be observed without pharmacotherapy [3][5]
- Specialist consultation triggers:
- All patients with suspected or confirmed ET should be referred to hematology/oncology [5]
- GI/hepatology consultation for splanchnic vein thrombosis or variceal bleeding [3]
- Perioperative consultation for elective surgery given elevated thrombotic and bleeding risk [3]
18. Follow Up / Return Precautions
- Follow-up timing: Regular hematology follow-up with periodic CBC monitoring; frequency guided by risk category and treatment status [3]
- Bone marrow biopsy should be repeated if there is clinical/laboratory suspicion of disease progression to myelofibrosis or before initiating cytoreductive therapy [3]
- Symptoms requiring immediate reassessment:
- New neurologic symptoms (sudden weakness, speech difficulty, vision loss)
- Chest pain, dyspnea
- Unilateral limb swelling or pain
- Severe or unexplained bleeding
- New constitutional symptoms (fevers, drenching night sweats, significant weight loss) [3]
- Patient counseling points:
- ET is a chronic condition with generally favorable prognosis, especially in younger patients [1]
- Medication adherence (aspirin, hydroxyurea) is critical for thrombosis prevention
- Smoking cessation and cardiovascular risk factor control are essential [1]
- No current therapy prevents disease transformation [1][5]
- Expected recovery course: ET is not curable but is manageable; most patients live near-normal lifespans with appropriate risk-stratified therapy [1][4]
References
1. Essential Thrombocythemia: A Review. — Tefferi A, Gangat N, Loscocco GG, et al. The Journal of the American Medical Association. 2025.
2. Essential thrombocythemia. — National Library of Medicine (MedlinePlus) 2014.
3. Myeloproliferative Neoplasms. — Updated 2026-01-22. National Comprehensive Cancer Network.
4. Essential Thrombocythemia. — Tefferi A, Pardanani A. The New England Journal of Medicine. 2019.
5. Thrombocytosis: Rapid Evidence Review. — Williams PM, Williams AL. American Family Physician. 2026.