Autoimmune Encephalitis Associated with Anti-gamma-aminobutyric Acid B Receptor Antibodies Mimicking Syncope.

Autoimmune encephalitis associated with autoantibodies to the gamma-aminobutyric acid B receptor (GABABR-AE) typically involves limbic symptoms with limbic abnormalities visible in brain magnetic resonance imaging (MRI). We herein report a case of a 48-year-old man with GABABR-AE whose initial presentation was limited to syncope without limbic symptoms or MRI abnormalities. Interestingly, serial MRI also revealed no abnormalities even after the appearance of limbic symptoms. Our findings suggest that GABABR-AE can initially mimic common syncope and that MRI findings may remain normal throughout the clinical course. Even if patients have normal MRI findings, GABABR-AE should be considered if limbic symptoms worsen.