Mild Encephalopathy with Reversible Splenial Lesion in an Adult Patient with Atypical Presentation

Introduction: Mild encephalopathy with reversible splenial lesion (MERS) is a clinical-radiological spectrum characterized by acute encephalopathy due to a reversible cause associated with a transient cytotoxic lesion affecting the splenium of the corpus callosum. It is considered a benign condition due to its reversibility and excellent prognosis. MERS is characterized by altered consciousness, delirium, and seizures. The time between the prodrome and the onset of encephalopathy usually ranges from 1 to 7 days. We present a case of MERS due to its atypical presentation. Case Presentation: A 60-year-old Caucasian female with a history of dyslipidemia and endometrial polyps presented to the emergency department with flu-like symptoms lasting 72 h, associated with two syncopal episodes. Brain magnetic resonance imaging (MRI) revealed a lesion in the splenium of the corpus callosum, with restricted diffusion on diffusion-weighted imaging and hyperintensity on fluid-attenuated inversion recovery sequences without enhancement after gadolinium infusion. Additional studies, including lumbar puncture, laboratory tests, and magnetic resonance spectroscopy, showed no pathological findings. A follow-up MRI performed 30 days later showed the complete resolution of the lesion. Conclusions: MERS has been classically described in children with concomitant infections, mostly viral. Increasing cases are being reported in adults. When encountering a patient with a cytotoxic lesion in the corpus callosum, MERS should be considered as a differential diagnosis; however, it is essential to rule out other etiologies with worse prognosis and specific treatments.