NMDAR-antibody encephalitis: Seizure semiology and EEG findings

N-methyl-D-aspartate receptor antibody encephalitis (NMDAR-Ab-E) is an autoantibody-mediated disorder, characterized by acute development of neuropsychiatric symptoms, seizures, movement disorders, and autonomic instability.

To describe acute seizure semiology and electroencephalogram (EEG) findings in patients with a first episode of NMDAR-Ab-E.

Medical records and EEG results were retrospectively evaluated from 14 adult patients with definite NMDAR-Ab-E, recruited between April 2009 and September 2017, and followed up until October 2024.

A total of 92.8% (13/14) were women with a mean age of 29.6 years. 85.7% (12/14) patients experienced seizures. Focal and/or generalized seizures were described at presentation or in the first days of the illness in 57% (8/14). EEGs showed diffuse slowing in 13/14 and this coexisted with epileptiform activity in 10/13; fast frequencies in 7/13 (potentially owing to a benzodiazepine effect); and asymmetric focal slowing in 6/13. Six patients had periods of rhythmic slow activity (focal or diffuse), without evolution to electrographic seizures. An extreme delta brush (EDB) pattern was recorded in 2/13 patients, and this was associated with non-convulsive status epilepticus in one of these individuals.

Most patients in this case series of NMDAR-Ab-E were young adult females with early focal and/or generalized seizures. Diffuse slowing in theta/delta range was the most common EEG finding, with or without epileptiform discharges, focal slowing, superimposed fast activities, and focal or diffuse rhythmic slowing. An EDB pattern was rare. Even with non-specific findings, EEG seems to be a sensitive tool to aid diagnosis and decision-making in NMDAR-Ab-E.