Dengue Fever Unmasking JAK2 Mutation-Related Polycythemia Vera Presenting With Extensive Splanchnic Venous Thrombosis and Hemorrhagic Complications: A Diagnostic and Therapeutic Challenge.

Dengue fever is a common arboviral infection characterized by fever, thrombocytopenia, and hemorrhagic manifestations, whereas thrombotic complications are relatively uncommon. We report a case of severe dengue infection revealing previously undiagnosed JAK2-related polycythemia vera (PV) complicated by extensive splanchnic venous thrombosis. A 58-year-old male patient with a history of diabetes mellitus and hypertension presented with a five-day history of fever, anorexia, and abdominal pain. Initial laboratory investigations demonstrated progressive thrombocytopenia, elevated hemoglobin, and increased hematocrit. During hospitalization, platelet counts continued to decline, and dengue serology returned positive. Computed tomography of the abdomen and pelvis revealed extensive splanchnic venous thrombosis involving the superior mesenteric, splenic, and portal venous systems, along with acute pancreatitis. The patient subsequently developed mucosal bleeding. Further evaluation revealed splenomegaly and a positive JAK2 V617F mutation, confirming underlying polycythemia vera. Due to concurrent bleeding and thrombosis, anticoagulation was initially deferred until hematologic stabilization was achieved. The patient was subsequently treated with anticoagulation and hydroxyurea, resulting in clinical recovery. This case highlights the rare coexistence of hemorrhagic and thrombotic complications in dengue fever and emphasizes the importance of considering underlying myeloproliferative neoplasms in patients presenting with atypical thrombosis, erythrocytosis, or splenomegaly.