Mild encephalitis/encephalopathy with a reversible splenial lesion (MERS).

Background: Mild encephalitis/encephalopathy with a reversible splenial lesion (MERS) is increasingly recognized as a clinicoradiological syndrome. Its etiology is diverse, encompassing a variety of triggers, including infections and metabolic abnormalities. Uniquely, MERS may present with psychiatric symptoms, such as delirium, visual hallucinations, and catatonia, posing diagnostic challenges. The variability of these neuropsychiatric symptoms necessitates early diagnosis through magnetic resonance imaging (MRI) to avoid prolonged antipsychotic treatment. Case Presentation: This report details a case of MERS in a 39-year-old male. The patient initially presented with headache, sore throat, and abnormal laboratory results: leukocytosis, neutrophilia with a left shift, elevated C-reactive protein (CRP) levels, and hyponatremia. On the fourth day of admission, he developed severe anxiety and restlessness, exhibited thoughts of death, and reported experiencing vivid hallucinations upon closing his eyes. MRI revealed a hyperintense lesion in the corpus callosum. A lumbar puncture showed no increase in cell count or protein. The patient showed a positive response to treatment with antibiotics and olanzapine, demonstrating rapid symptomatic improvement. A follow-up MRI on the 11th day showed complete resolution of the brain lesions. Six months later, no neurological or psychiatric sequelae were noted. The patient's clinical progression and imaging findings led to a definitive diagnosis of MERS. Conclusion: The early presentation of symptoms such as restlessness, hallucinations, and death ideation played a critical role in diagnosing MERS, with early MRI examination being instrumental in both diagnosis and preventing prolonged antipsychotic medication use.