Seizures in autoimmune encephalitis: specific features based on a systematic comparative study

Objective. To highlight specific characteristics of seizure semiology and EEG features associated with different subtypes of autoimmune encephalitis (AE). Methods. We systematically reviewed the seizure semiology and all the EEG recordings from patients with AE managed in a tertiary referral centre for epilepsy and a neuro-intensive care unit. Each characteristic across the different subtypes of AE was compared by post hoc analysis. Results. We identified 66 patients with anti-neuronal antibody-mediated AE or Rasmussen's encephalitis (RE) experiencing seizures, which were the most frequent symptom at onset. Anti-NMDAR and anti-LGI1 AE accounted for the majority of patients; 41% and 24%, respectively. We isolated specific semiological features, such as early tonic-clonic seizures (TCS) in anti-NMDAR AE, early mesial temporal lobe seizures with emotional symptoms in anti-GAD AE, somatosensory seizures in RE, and a lower frequency of TCS in anti-LGI1 AE. EEG analysis also provided additional insights into distinguishing the subtypes based on: (1) generalized rhythmic delta activity, which was more sensitive than extreme delta brush in identifying anti-NMDAR AE among all subtypes; and (2) temporal interictal epileptiform activity and temporal seizures on EEG in anti-GAD AE. We identified a new EEG pattern consisting of temporal low-voltage and periodic spikes associated with ipsilateral hippocampal abnormalities on MRI, which could be a sign of inflammatory mesial temporal involvement. Significance. Specific clinical and EEG features can be useful in guiding the diagnosis of a subtype of AE with acute symptomatic seizures, particularly before the results of anti-neuronal antibody testing are available.