Abstract
BACKGROUND: Currently, Listeria monocytogenes (LM) meningoencephalitis is rare in immunocompetent individuals, and its association with mild encephalitis/encephalopathy with a reversible splenial lesion (MERS) is even more uncommon. CASE PRESENTATION: We report a case of an immunocompetent adult female presenting with headache, fever, and vomiting, accompanied by hyponatremia and atypical splenial lesions of the corpus callosum on brain MRI. Both cerebrospinal fluid (CSF) metagenomic next-generation sequencing (mNGS) and culture confirmed LM infection, leading to a diagnosis of LM meningoencephalitis. The patient recovered completely after treatment with meropenem. CONCLUSION: This case highlights distinct clinical manifestations, laboratory findings, imaging features, and therapeutic responses in immunocompetent patients compared to immunocompromised populations. The atypical radiological presentation and favorable outcome underscore the importance of early pathogen identification via advanced diagnostics like mNGS. Our findings provide valuable insights into the heterogeneity of LM infections and emphasize the need for heightened clinical vigilance even in immunologically normal hosts.