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

Abstract

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.

Clinical Characteristics of Anti-GABA-B Receptor Encephalitis

“…For example, Ohta et al reported a case of GABA-B encephalitis with multifocal hyperperfusion in the epithelia and subcortical MRI (7). Kitazaki et al reported a case of GABA-B encephalitis with syncope (8). Yao et al summarized seven, eight and 11 patients, respectively (9)(10)(11).…”

Case Report: Anti-GABAA Receptor Encephalitis in a Dog

“…On average, a diagnosis in humans is made 2 months after symptom onset or in a time span of 1 week to 5 years ( 14). An unremarkable MRI has been reported in 26.6% of patients with GABA B R encephalitis (34,35). Interestingly, in anti-NMDA-R encephalitis, unremarkable MRIs are described in 45% of patients (36,37).…”

Anti-GABAB Receptor Encephalitis Presenting with Atypical Corticobasal Syndrome in a Patient with Parkinson’s Disease

“…5 Movement disorders have been described in 14.3% of patients with anti-GABABR encephalitis, the most common being myoclonus and ataxia. 4,5 Rarer clinical presentations of anti-GABABR encephalitis, limited to single case reports, include recurrent syncope, 6 and amyotrophic lateral sclerosis. 7 It is possible that the pre-existing diagnosis of PD in our patient contributed somewhat to the CBS phenotype.…”

“…4,5 Normal MRI findings despite clinical and EEG progression have also been reported. 6 Anti-GABABR encephalitis has a high mortality, especially if associated with underlying malignancy, commonly small-cell lung carcinoma. 4 Immune-mediated therapies, such as intravenous steroids, intravenous immunoglobulins and plasma exchange, with diseasemodifying therapies are used with reasonable success.…”

“…Frequently observed changes include unilateral or bilateral T2/FLAIR white matter hyperintensities in the mesial temporal lobes and rarely atrophy or hypointensity of the mesial temporal lobe [ 4 , 5 ]. Normal MRI findings despite clinical and EEG progression have also been reported [ 6 ]. Anti-GABA B R encephalitis has a high mortality, especially if associated with underlying malignancy, commonly small-cell lung carcinoma [ 4 ].…”