Non-cirrhotic portal-splenic-mesenteric vein thrombosis unmasking JAK2 V617F-positive polycythemia vera.

Non-cirrhotic splanchnic venous thrombosis (SVT) can occur in myeloproliferative neoplasms. We report the case of a 69-year-old man who presented with a 2-week history of epigastric pain and was found to have simultaneous portal, splenic, and superior mesenteric vein thromboses in the absence of cirrhosis or malignancy on contrast-enhanced computed tomography. Laboratory testing revealed elevated haemoglobin/haematocrit with a low-normal mean corpuscular volume (83 fL), biochemical evidence of iron restriction, and an inappropriately low serum erythropoietin level. On further testing, JAK2 V617F was positive, and bone marrow findings supported the diagnosis of polycythemia vera (PV). This presentation is compatible with an iron-deficiency-modified PV phenotype (sometimes referred to as "masked PV"), in which iron restriction can attenuate or obscure typical erythrocytosis, and extensive non-cirrhotic SVT effectively unmasked the underlying clonal disorder. Edoxaban 30 mg once daily (body weight < 60 kg) was initiated without interruption or bleeding, and therapeutic phlebotomy was initiated to control the hematocrit. Follow-up computed tomography on day 78 demonstrated marked thrombus reduction with partial re-opacification of the main portal vein, and the patient continued to have a stable clinical course. This case highlights triple-site, non-cirrhotic SVT as a potential presenting feature of PV and supports early JAK2 V617F and erythropoietin testing, coupled with parallel anticoagulation and PV-directed management, in unexplained non-cirrhotic SVT.