The Hypoxia Trap: Worsening Sickle Cell Disease in the Setting of Tetralogy of Fallot.

BACKGROUND: Tetralogy of Fallot (TOF) is the most common cyanotic congenital heart disease and predisposes affected children to thrombotic complications due to chronic hypoxia and polycythemia. Sickle cell disease (SCD) further increases the risk of vaso-occlusion through erythrocyte sickling and endothelial dysfunction. The coexistence of TOF and SCD is rare and creates complex diagnostic and therapeutic challenges with significant risk of catastrophic neurological events. CASE PRESENTATION: We report a 14-month-old female with known TOF who presented with acute left-sided hemiparesis, fever, and seizures. Brain computed tomography with angiography revealed extensive bilateral ischemic infarctions with complete thrombosis of both middle cerebral arteries and occlusion of the right internal carotid artery. Haematological evaluation confirmed previously un-diagnosed SCD with an HbS fraction of 60.2%. Despite intensive therapy including oxygen, intravenous hydration, hydroxyurea, antiepileptic drugs, and exchange transfusion that reduced HbS to 28.9%, the child developed progressive encephalopathy and died. Chronic hypoxia from TOF combined with SCD-related sickling likely precipitated catastrophic cerebrovascular thrombosis. CONCLUSION: This case highlights the synergistic thrombotic risks of TOF and SCD, emphasising the critical need for routine hemoglobinopathy screening in children with cyanotic heart disease, especially in high-prevalence regions. Early diagnosis, proactive use of vasopressors to optimise oxygenation, and multidisciplinary management are essential to improve outcomes. Aggressive preventive interventions are essential to reduce morbidity and mortality in patients presenting with these rare coexisting pathologies. Enhanced screening awareness, stroke-preventing strategies and timely surgical intervention for TOF could improve prognosis in this rare, high-risk dual pathology.