Reversible Splenial Lesion Syndrome Due to Anti-NMDA Receptor Encephalitis Manifesting as Delusional Disorder: A Case Report and Literature Review.

Reversible splenial lesion syndrome (RESLES) is a transient neuroimaging finding associated with various etiologies. Although RESLES has been reported in diverse conditions, including medications, metabolic disorders, and infections, its occurrence in autoimmune encephalitis, such as anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis, is rarely described. This report details a rare case demonstrating this association. A 24-year-old woman presented with a 4-month history of progressive behavioral changes, which culminated in paranoid delusions and catatonic symptoms. The initial diagnosis was delusional disorder, but her condition rapidly worsened with fever. A brain magnetic resonance imaging (MRI) revealed a reversible lesion in the splenium of the corpus callosum (SCC). Laboratory tests confirmed the presence of anti-NMDAR antibodies in her cerebrospinal fluid, and an abdominal computed tomography scan revealed bilateral ovarian teratomas. She was treated with high-dose corticosteroids and intravenous immunoglobulin, followed by surgical removal of the teratomas. Rituximab was later administered for long-term immunomodulation. The patient's clinical state, including her psychiatric and neurocognitive symptoms, gradually improved significantly. A follow-up MRI 2 months after discharge confirmed complete resolution of the SCC lesion. This case highlights that RESLES can be the initial neuroimaging manifestation of anti-NMDAR encephalitis. It underscores the critical importance of considering autoimmune causes of acute-onset psychiatric symptoms and atypical neuroimaging findings. Early and appropriate diagnosis and treatment of the underlying autoimmune etiology are essential for favorable neurological and psychiatric outcomes.