Asymptomatic Essential Thrombocytosis Presenting with Extrahepatic Portal Vein Thrombosis: A Case Report

BACKGROUND Essential thrombocytosis (ET) is a myeloproliferative neoplasm variant that leads to excessive platelet production in the bone marrow. Janus kinase 2 (JAK2) mutation is observed in 60% of ET cases. The risk of thrombosis increases with the presence of this mutation. ET can cause systemic thrombosis, including extra-portal vein thrombosis (EHPVT). In patients with ET-induced EHPVT, varied symptoms generally occur. However, our case was asymptomatic. This condition is relatively rare. CASE REPORT A 49-year-old woman presented to our hospital for a detailed clinical examination 1 month after a health examination, and blood tests revealed microcytic anemia and thrombocytosis. The patient had no current concerns and had no relevant medical or alcohol consumption history. Esophagogastroduodenoscopy demonstrated esophageal varices, with portal hypertension suspected as the underlying cause. Contrast-enhanced computed tomography scans revealed a thrombus in the portal vein, but liver cirrhosis and a tumor were ruled out. JAK2 mutation was positive, which led to myeloproliferative neoplasms being considered as the differential diagnosis. Bone marrow biopsy demonstrated many mature megakaryocytes with large and irregular nuclei and platelet aggregation in the field of view, leading to the diagnosis of ET. CONCLUSIONS This case study describes a patient with EHPVT caused by JAK2-positive ET. This case report emphasizes that physicians should consider myeloproliferative neoplasms as part of their differential diagnosis when presented with EHPVT.