EEG leading to the diagnosis of limbic encephalitis.

Limbic encephalitis is characterized by subacute onset of short-term memory loss, seizures, sleep disturbances, as well as psychiatric and behavioral symptoms. A subgroup is associated with voltage-gated potassium channel antibodies (VGKC-Abs). In many cases, brain magnetic resonance imaging (MRI) demonstrates hyperintense areas in the medial part of the temporal lobe. Also, pleiocytosis is frequently found. In this study, we describe a 69-year-old man with VGKC-Abs limbic encephalitis with generalized tonic-clonic seizures, increasing memory deficits, visual hallucinations, depression, and severe insomnia. Brain MRI and cerebrospinal fluid (CSF) were normal, while the electroencephalogram (EEG) showed bilateral frontal and temporal intermittent rhythmic delta activity with disorganization and slowing of background activity, ultimately leading to the diagnosis of limbic encephalitis. The patient improved markedly after starting immunosuppressive therapy, both clinically and electrophysiologically. In addition to temporal lobe involvement on the brain MRI and CSF inflammation, we propose EEG abnormalities as an additional diagnostic criterion for limbic encephalitis.