Neurocognitive sequelae following seronegative anti-NMDA receptor encephalitis with ovarian teratoma in a pediatric patient: A six-year follow-up case report.

Background: Anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis is the commonest form of autoimmune encephalitis of childhood. However, little information is captured with formal neuropsychological testing. When the pre-illness history is incomplete, it is also hard to judge how much of the residual picture reflects the encephalitis itself rather than an earlier neurodevelopmental vulnerability. Case presentation: We describe the case of an adopted girl who became acutely unwell at 11 years of age, with a rapid neuropsychiatric deterioration, seizures and abnormal movements. A mature ovarian teratoma was found and removed, and the clinical course, serial EEGs and response to immunotherapy supported a diagnosis of probable anti-NMDAR encephalitis. Serum and cerebrospinal fluid (CSF) antibodies were negative, although the samples were taken late and after treatment had begun. She was managed with corticosteroids and intravenous immunoglobulin. Six years on, formal testing showed largely intact verbal comprehension but clear weaknesses in executive function, attention, processing speed and verbal memory. She met criteria for autism spectrum disorder; overall cognitive ability was in the low average range. Conclusion: This case shows how a paraneoplastic, immune-mediated insult to the developing brain can leave a lasting cognitive mark, how easily seronegative disease is missed, and why it is often neuropsychological assessment, rather than imaging, that reveals the residual burden.