- Primary bone marrow problem related to JAK2 mutation
- Must r/o secondary (reactive) causes thrombocytosis, including: Iron deficiency; Inflammation--> RA, Stills dz, other; Chronic infection--> TB, other; Post splenectomy; Para-neoplastic; Hemolysis
- 20% of patients present at age < 40
- Asx until platelets significantly elevated
- Sx related to arterial or venous thrombotic events→ stroke, MI, dvt/pe
- Interestingly, some patients have increased risk bleeding
- Splenomegaly in 40% of those w/ET
- Progressively increasing platelet counts > 450k (can exceed 1 million)
- Review of peripheral smear
- + JAK2 mutation
- Often bone marrow bx