Rasmussen-Like Asymmetric Cortical Atrophy in Anti-NMDA Receptor Encephalitis

An 18-year-old man presented with 1 week of insomnia and headache, followed by erratic behavior, encephalopathy, seizures, and left-sided weakness. Brain MRI demonstrated cortical T2/FLAIR hyperintensity predominantly involving the right cerebral hemisphere, followed by progressive right-greater-than-left cortical volume loss over 2 months. FDG-PET showed extensive hypometabolism, predominantly affecting the right cerebral hemisphere and thalami. CSF revealed lymphocyte-predominant pleocytosis (87 cells/μL), with normal protein and glucose. Anti-NMDA receptor IgG was positive in serum and CSF by cell-based assay (titer not available). Body FDG-PET was negative for malignancy. He was treated with intravenous corticosteroids, immunoglobulin, and rituximab. At 6-month follow-up, he followed simple commands, walked independently with a spastic gait, and was seizure-free on 2 anti-seizure medications. Repeat serum anti-NMDA receptor IgG remained positive at 1:40. While asymmetric cortical atrophy is classically associated with Rasmussen encephalitis, autoimmune encephalitis can rarely have a similar radiographic appearance. The presence of milder contralateral imaging abnormalities and persistent anti-NMDA receptor seropositivity after clinical stabilization supports an atypical presentation of anti-NMDA receptor encephalitis. This case expands the literature on Rasmussen-like autoimmune encephalitis and potential overlap syndromes.