2616 Unilateral posterior reversible encephalopathy syndrome: a case of Hickam’s Dictum

ObjectiveTo describe a rare and diagnostically challenging case of unilateral posterior reversible encephalopathy syndrome (PRES), contralateral to a chronically occluded right internal carotid artery (ICA), in a patient with multiple sclerosis (MS).BackgroundPRES is a clinicoradiological diagnosis based on typical clinical features and risk factors, supported by MRI findings. MRI typically shows bilateral cortical and subcortical vasogenic oedema. Cases involving unilateral vasogenic oedema are very rare.Case PresentationWe report the case of a 66-year-old female brought to the emergency department as a code stroke for right-sided hemiplegia preceded by her first ever seizure. She was confused and severely hypertensive on arrival. CT stroke protocol showed a chronically occluded right ICA, delayed cerebral perfusion in the right anterior circulation and no core infarct. MRI findings were consistent with vasogenic oedema in the superior left frontal and parietal lobes. The patient had multiple sclerosis with preexisting periventricular white matter lesions, one of which had enlarged on her most recent surveillance MRI. She had not been taking disease modifying therapy for the past 10 years. CSF studies for infectious aetiologies were negative. A left renal artery occlusion was identified and treated conservatively. The hypertension resolved with medical therapy. The patient recovered and a follow-up MRI showed resolution of vasogenic oedema.ConclusionThis case illustrates a rare presentation of unilateral PRES. An occluded ICA protected the ipsilateral anterior circulation from the significantly elevated perfusion pressures, and subsequent endothelial dysfunction, experienced by the contralateral hemisphere in the setting of severe hypertension.