Subclinical Temporal EEG Seizure Pattern in LGI1-antibody-mediated Encephalitis

Leucine-rich glioma inactived-1 (LGI1) antibodies are associated with limbic encephalitis and distinctive seizure types, which are typically immunotherapy-responsive. Although nonspecific electroencephalography (EEG) abnormalities are commonly seen, specific EEG characteristics are not currently understood to be useful for suspecting the clinical diagnosis. Based on initial observations in two patients, we analyzed the clinical features and EEG recordings in a larger series of patients (n = 9) and describe a novel ictal pattern that can suggest the diagnosis of LGI1-antibody-mediated encephalitis, even in the absence of typical clinical features. As expected, psychiatric and cognitive symptoms were common, as were tonic seizures associated with EEG electrodecremental events (often with the so-called faciobrachial dystonic semiology). Remarkably, in five patients, a near absence of interictal epileptiform discharges contrasted with frequent subclinical temporal lobe seizures, at times triggered by hyperventilation. This latter EEG pattern may facilitate early diagnosis of this serious but potentially treatable condition.