Posterior Reversible Encephalopathy Syndrome Associated With Severe Autoimmune Hyperthyroidism: A Case of Cortical Visual Loss Mimicking Posterior Cerebral Artery Infarction

Posterior reversible encephalopathy syndrome (PRES) is a clinico-radiological syndrome characterised by acute encephalopathy, seizures, headache and visual disturbance, with neuroimaging typically demonstrating predominantly posterior vasogenic oedema.Although severe hypertension, renal dysfunction, sepsis and exposure to cytotoxic or immunosuppressive therapies are well-recognised precipitants, PRES associated with autoimmune thyroid disease is uncommon.We report the case of a 55-year-old woman with no previous history of thyroid disease who presented with acute encephalopathy, fever and hypoxia and was subsequently found to have severe autoimmune hyperthyroidism consistent with Graves' disease.Recurrent focal and generalised seizures and profound bilateral visual loss complicated her clinical course.Initial neuroimaging demonstrated only chronic infarcts.Subsequent MRI revealed right occipital cortical and subcortical abnormalities with diffusion restriction, which were initially interpreted as an acute posterior cerebral artery territory infarction.However, the combination of encephalopathy, seizures, visual loss, and interval radiological improvement prompted tertiary neuroradiology review, and the imaging abnormalities were subsequently considered consistent with PRES.Cerebrospinal fluid analysis and extensive infectious, neuronal and paraneoplastic antibody testing did not identify an alternative inflammatory or infectious cause.Management included treatment of severe thyrotoxicosis with carbimazole, antiepileptic therapy and treatment of concurrent systemic infection and acute kidney injury.Visual function gradually improved from perception of light only to recognition of colours and objects, although significant visual and cognitive impairment persisted at follow-up.This case highlights severe autoimmune hyperthyroidism as a potential contributor to PRES in the presence of additional systemic stressors.It demonstrates the diagnostic challenge posed by occipital PRES with diffusion restriction, which can mimic posterior circulation infarction.Recognition of the characteristic clinical-radiological evolution and multidisciplinary neuroradiological review are important to avoid misdiagnosis and guide appropriate management.