Essential Thrombocythemia

Essential thrombocythemia is a myeloproliferative disease characterized by bleeding tendency and thrombosis; defined as peripheral platelet count exceeding the normal upper limit 400x10^9/L, with abnormal platelet function and excessive marrow megakaryocyte proliferation. Because recurrent bleeding is common, it is also called hemorrhagic thrombocythemia. Incidence is not high; patients are mostly over 40. Main pathophysiologic features: clonal, reactive/secondary, familial/hereditary; treatment remains to be solved.

Common Symptoms

Insomnia; splenic infarction; venous thrombosis; fatigue; sensory disturbance

Causes and Pathogenesis

(A) Etiology: Thrombocytosis - Essential thrombocythemia is caused by clonal proliferation of a single abnormal pluripotent stem cell; megakaryocyte number and average volume increase, platelet production up to 15-fold normal rate. Stem-cell disease - G6PD isoenzyme studies confirm this is also a pluripotent-stem-cell clonal disease causing persistent marked marrow megakaryocyte proliferation, increased platelet production plus release from splenic/hepatic stores, but platelet lifespan is mostly normal. Platelet functional defect - adhesion/aggregation decreased, platelet factor 3 reduced, serotonin reduced, release abnormal; some patients have abnormal coagulation and increased capillary fragility. Excess activated platelets produce thromboxane, causing aggregation/release and microthrombosis; late cases may have splenic/other-organ extramedullary hematopoiesis. (B) Pathogenesis: Clonal nature was established when an isoenzyme of G-6-PD was found in erythroid lineage of a female case - heterozygous for G-6-PD types A and B; same abnormality found in erythroid/granulocytic progenitors of another patient. Why phenotype mainly expresses in megakaryocyte-platelet lineage is unclear; possibly the abnormal clone has a growth advantage on megakaryocytic regulators, or mutation occurred in a pluripotent stem cell biased toward megakaryocytic differentiation. Histology and in-vitro megakaryocyte culture show abnormal expansion of marrow megakaryocyte progenitors; patient marrow/blood CFU-MEG is markedly increased vs normal/secondary-thrombocytosis controls, with abnormal clone size and endoreduplication; CFU-MEG grows even without exogenous growth factors; a few cases also have increased CFU-GM and BFU-E. With megakaryocyte number/volume increased, platelet production up to 15-fold normal; lifespan usually normal, sometimes shortened due to splenic destruction. Mechanism of bleeding/thrombosis from marked thrombocytosis is uncertain; generally abnormal platelet function is the main bleeding cause, some patients have reduced coagulation factors. Markedly elevated platelets cause hyperaggregable thrombosis. Intrinsic defects: reduced intraplatelet serotonin, reduced adhesion, reduced ADP/epinephrine-induced aggregation. Megakaryocyte proliferation is not only marrow but may involve extramedullary tissues; liver/spleen may have megakaryocytic hyperplastic foci. Because malignancy is low and growth slow, liver/spleen are moderately enlarged. No external etiologic factor has been found.

Treatment

Drug therapy, supportive therapy

Preventive Measures

Patients need regular visits to monitor peripheral blood counts, adjust medication timely, understand disease evolution, self-protect against trauma/bleeding. Low-dose enteric aspirin reduces platelet count and aggregation.

Department to Visit

It is recommended to visit the Hematology department; an appointment can be booked on this platform before the visit.

Warm reminder: The above information is for health science reference only and cannot replace professional medical diagnosis. If you have related symptoms, please seek medical attention at a regular hospital promptly.