Seizure As the Sentinel Event: An Atypical Presentation of Anti-N-Methyl-D-Aspartate (NMDA) Receptor Encephalitis in a Young Adult Male

This case report details an atypical presentation of anti-N-methyl-D-aspartate (NMDA) receptor encephalitis in a 21-year-old male, characterized by a "seizure-first" phenotype. The patient’s initial generalized tonic-clonic seizure led to a misdiagnosis of epilepsy, and subsequent psychiatric symptoms were incorrectly attributed to the side effects of antiepileptic medication or a new, undiagnosed psychiatric disorder. This resulted in an involuntary psychiatric admission and a delay in diagnosis and, thus, definitive treatment. Once the Graus criteria for probable anti-NMDA receptor encephalitis were met (presence of at least four out of six neuropsychiatric symptom categories, an abnormal electroencephalogram (EEG), and the reasonable exclusion of alternative causes), the patient was empirically treated with high-dose steroids. Upon detecting anti-NMDA receptor antibodies at a serum titer of 1:1000 and a cerebrospinal fluid (CSF) titer of 1:100, the treatment regimen was escalated to include plasmapheresis. In this patient's case, earlier consideration of autoimmune encephalitis during his initial presentation of new-onset seizures and rapid psychiatric decline could have prevented the diagnostic delay and involuntary psychiatric admission.