Mild Encephalitis/Encephalopathy With a Reversible Splenial Lesion (MERS) Type II in an Adult: A Case Report and Diagnostic Insight

Mild encephalitis/encephalopathy with a reversible splenial lesion (MERS) is a rare clinico-radiological syndrome characterized by transient lesions in the splenium of the corpus callosum on magnetic resonance imaging (MRI). Although increasingly recognized in pediatric populations, MERS remains underdiagnosed in adults. We report a case of adult-onset MERS that presented with nonspecific neurological symptoms following a respiratory prodrome. Brain MRI demonstrated the characteristic diffusion-restricting splenial lesion, which guided the diagnostic approach. The rapid and complete resolution of both clinical symptoms and radiological abnormalities confirmed the diagnosis. This case highlights the importance of including MERS in the differential diagnosis of adult encephalopathy, particularly due to its excellent prognosis and potential to mimic more serious neurological conditions.