An Atypical Presentation of Posterior Reversible Encephalopathy Syndrome (PRES): Sticking to the Basics.

Posterior reversible encephalopathy syndrome (PRES) is a reversible clinico-radiological condition primarily affecting the occipito-parietal regions. Thalami, brainstem, and cerebellar involvement with posterior fossa oedema are rare manifestations of this condition. We present the case of a 66-year-old male with a travel history to Thailand who was found collapsed on the floor two weeks after his return. He did not have any history of neurological or systemic symptoms. A head computed tomography (CT) showed extensive posterior fossa and brainstem oedema resulting in tonsillar herniation and mild hydrocephalus. Magnetic resonance imaging (MRI) study revealed widespread symmetric T2/FLAIR changes in the supratentorial and infratentorial brain parenchyma, microhemorrhages, and florid punctate enhancement in the affected regions. After his initial investigations, the differential diagnosis included acute demyelinating encephalomyelitis (ADEM) and viral rhomboencephalitis. Blood pressure was elevated on admission and intensive care unit stay. Upon achieving blood pressure control, the patient's clinical picture improved and a diagnosis of PRES was made. Our case highlights how confounding factors make the diagnostic process challenging. Atypical presentations of PRES are rare but should be considered in patients with risk factors such as uncontrolled hypertension and acute neurological symptoms in the context of MRI findings of vasogenic oedema.