Abstracts

Rationale: We present a case of LGI1 autoimmune synaptic encephalitis with associated persistent focal EEG abnormalities, which resolved with immunologic treatment.Methods: Case report and literature review. BACKGROUND 70 year old male with no history of tumors presented with multiple episodes of speech arrest and lapse of awareness. MRI brain was normal. Post-ictal EEG showed bitemporal slowing, left greater than right. Seizures were resolved by week eight after treatment with levetiracetam, followed by lamotrigine. In the fifth month, he began to have subacute amnestic episodes and cognitive decline. St. Louis Memory Assessment Scale (SLUMS) testing was 22/30. 24-hour video EEG was performed to rule out subclinical seizures. No seizures or interictal discharges were seen, but the EEG showed pronounced continuous slowing in bicentro-parietal regions. Repeat MRI brain showed subtle left mesial temporal T2 hyperintensity. Laboratory workup revealed positive neuronal VGKC(>0.20 nmol/L), LGI1(positive) and GAD-65(2.2 nmol/L) antibodies. Neoplastic evaluation was negative. In the eighth month, his cognition worsened and he was started on methylprednisolone 500mg bid for 3 days followed by IVIG, 65 grams daily for 4 days. He was discharged on prednisone 10mg daily. Immediate subjective symptomatic improvement was noted, and one month later, repeated SLUMS test was 27/30 and EEG was normal.Results: To our knowledge, there are no other reported cases of these EEG findings, which resolved with treatment of the condition.Conclusions: LGI1 autoimmune encephalitis is a rare but treatable condition typically associated with faciobrachial dystonic seizures, cognitive impairment, and hyponatremia. Persistent and pronounced focal bihemispheric slowing provided a clue for further investigation and resolved with immunomodulation. These EEG changes have not been reported and may act as an additional biomarker for this condition. Additionally, this is the first case report of autoimmune synaptic encephalitis with both positive LGI1 and GAD-65 antibodies.