Hyperviscosity-Related Ischemic Stroke in an Adolescent With Unrepaired Tetralogy of Fallot: A Case Report From a Resource-Limited Setting.

Tetralogy of Fallot (TOF) is the most common cyanotic congenital heart disease. Chronic hypoxemia in uncorrected TOF causes compensatory erythrocytosis and hyperviscosity, predisposing to cerebrovascular complications. Stroke in this context is rare but clinically significant, especially in resource-limited settings where access to imaging and surgical correction is restricted. We report a 17-year-old male with unrepaired TOF and secondary polycythaemia who presented with recurrent headaches and dizziness following repeated phlebotomy. He subsequently developed acute right-sided weakness and aphasia. Brain MRI revealed an acute ischemic infarction in the left basal ganglia and insular region. Echocardiography confirmed TOF anatomy without thrombus or new shunt changes. The patient was treated with supportive measures, antiplatelet therapy, and hydration; further phlebotomy was withheld. Neurologic improvement occurred with rehabilitation, though residual weakness persisted at discharge. This case highlights ischemic stroke as a rare but serious manifestation of hyperviscosity in cyanotic congenital heart disease. In resource-limited settings, pragmatic diagnostic strategies and cautious hematologic management are vital. Early recognition of neurologic symptoms, avoidance of excessive phlebotomy, and timely referral for definitive TOF repair are essential to prevent recurrence and improve outcomes.