Myeloproliferative neoplasm as a cause of splanchnic vein thrombosis.

Splanchnic vein thrombosis (SVT) is a rare, life-threatening condition that is often associated with cirrhosis, pancreatic malignancy and thrombophilia. Myeloproliferative neoplasms are under-recognised causes, posing diagnostic challenges. In this case, we present a male in his late 20s with a history of unprovoked pulmonary embolism and portal/splenic vein thrombosis, on indefinite anticoagulation therapy presenting 3 years later due to abdominal pain. Imaging revealed cirrhosis, cavernous transformation of the main portal vein and splenomegaly. These findings and a prior negative hypercoagulability workup prompted haematology consultation. Bone marrow biopsy confirmed primary myelofibrosis (PMF), demonstrating 90% cellularity, megakaryocytic hyperplasia, MF-3 fibrosis and calreticulin (CALR) mutation. This case underscores PMF as a treatable cause of SVT in young patients with recurrent thrombosis and highlights the consequences of diagnostic inertia, as marked thrombocytosis at initial presentation was overlooked. When Janus Kinase 2 (JAK2) is negative, CALR testing should be pursued to enable early diagnosis and targeted therapy.