Cerebral Infarction As the Presenting Feature of Janus Kinase 2 (JAK2) V617F-Positive Polycythemia Vera: A Case Report

Polycythemia vera (PV) is a clonal myeloproliferative neoplasm driven predominantly by the Janus kinase (JAK)2 V617F mutation and characterized by an absolute increase in red cell mass.Because its early features are frequently nonspecific, PV can remain undetected until a thrombotic event -commonly an arterial ischemic stroke -brings the patient to medical attention.We report a 56-year-old woman with a two-year history of systemic hypertension who presented with a six-day history of insidious, distally predominant weakness of the left lower limb, with no other neurological deficit or limb involvement recorded.Magnetic resonance imaging of the brain demonstrated an acute infarct in the right high frontal region together with chronic small-vessel ischemic changes.Laboratory evaluation revealed marked erythrocytosis (hemoglobin 19 g/dL, hematocrit 62%), a normal serum erythropoietin level, and a positive JAK2 V617F mutation; bone marrow biopsy showed erythroid hyperplasia, with no further morphological detail available.A working diagnosis of PV was made on the combined clinical, hematological, and molecular findings.In the absence of a documented alternative cause on the available work-up, PV was considered a plausible contributor to the infarction.The patient was started on dual antiplatelet therapy and a high-intensity statin for secondary stroke prevention, underwent serial therapeutic phlebotomy (hematocrit falling from 62% to 50.8% by day 22), and was discharged on hydroxyurea 500 mg twice daily.Left lower-limb power improved from 0/5 at admission to 3/5 at discharge on day 9.This case illustrates the importance of considering PV in the differential diagnosis of stroke, particularly when routine blood counts show unexplained erythrocytosis, since early recognition and cytoreductive therapy may reduce the thrombotic risk, though longer follow-up and a more complete stroke work-up are needed to confirm this in the individual patient.