A Case of Anti-N-Methyl-D-Aspartate Receptor (NMDAR) Encephalitis With Video-Documented Psychogenic Nonepileptic Seizures (PNES)-Mimicking Episodes Initially Considered as Somatic Symptom Disorder

Anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis is an autoimmune disorder characterized by psychiatric symptoms, seizures, and dyskinesias. This case report describes a 30-year-old woman who was initially suspected of having a somatic symptom disorder because of the development of seizures mimicking psychogenic non-epileptic seizures (PNES). At presentation, she was able to engage in conversation and follow instructions, but exhibited slight fever, sensory abnormalities, and non-stereotypical seizures. Over the course of two weeks, she fell into a catatonic stupor. Cerebrospinal fluid (CSF) analysis revealed only mild pleocytosis with CSF-restricted oligoclonal bands. Electroencephalogram, which was unremarkable at presentation, subsequently showed an extreme delta brush pattern. NMDAR antibodies were detected in CSF with two independent assays, confirming the diagnosis of anti-NMDAR encephalitis. First-line immunotherapy with steroids, plasma exchange, and immunoglobulins was ineffective, but second-line immunotherapy with cyclophosphamide led to improvement. This case underscores the importance of considering anti-NMDAR encephalitis in patients with PNES-mimicking episodes, which can be misleading and delay appropriate diagnosis and treatment.