MRI Characteristics of Autoimmune Encephalitis With Autoantibodies to GABAA Receptor: A Case Series.

Background And Objectives: To characterize the clinical and neuroimaging phenotypes of patients with autoantibodies to γ-aminobutyric acid type A receptor (GABAR).

Methods: Ten patients with autoantibodies against GABAR from Huashan Hospital Autoimmune Encephalitis cohort were identified. We used MRI assessments and clinical examinations to summarize major clinical profile and visualize and quantify lesion distribution features. The relationship between clinical features, neuroimaging phenotypes, and topology of GABAR expression were further investigated.

Results: The median age at onset of 10 patients (8 male patients and 2 female patients) with anti-GABAR encephalitis was 41.5 years (range: 17-73 years). All patients had prominent seizures and multifocal spotted or confluent lesions involved in limbic, frontal, and temporal lobes on brain MRI. Bilateral but asymmetric lesions in cingulate gyri were observed in all patients. These involved lesions could change dynamically with immunotherapies and relapse. Distribution of patients' brain MRI lesions was positively correlated with gene expression level of β3 subunit-containing GABAR (Spearman ρ = 0.864, = 0.001), the main target of autoantibodies. According to topology of lesions, patients with anti-GABAR encephalitis could be classified into 2 clinical-radiological types: confluent type with bilateral confluent lesions involved in almost all limbic, frontal, and temporal lobes and spotted type with multiple scattered small-to-medium patchy lesions. Patients with confluent type exhibited worse clinical presentations and outcomes when compared with those with spotted type (maximum modified Rankin scale [mRS]: 5 [5-5] vs 3.5 [3-4], respectively, = 0.008; follow-up mRS: 4 [2-6] vs 0.5 [0-1], respectively, = 0.016).

Discussion: Anti-GABAR encephalitis has distinctive neuroimaging phenotype. Cingulate gyri were frequently involved in this disorder. The topology of lesions might be associated with the distribution of β3 subunit-containing GABAR and reflected patients' disease severity and outcomes.