Clinical Characteristics and Prognostic Clinical Factors of Anti-Gamma Acid-B Receptor (GABAB-R) Encephalitis in Türkiye: A Multicenter Study

Abstract

Introduction: GABAB-R encephalitis is a rare recognized autoimmune disease. This study investigates the clinical and laboratory features, treatment response, prognosis, and malignancy associations in GABAB-R encephalitis. Methods: We included consecutive encephalitis patients with GABAB-R autoantibodies and retrospectively analyzed their clinical data, neuroimaging, EEG findings, seizure characteristics, treatment responses, prognosis, and cancer presence. Prognosis was classified using the final Modified Rankin Score (mRS), with mRS > 2 indicating poor prognosis. Results: There were 17 patients with GABAB-R antibodies (12 males). The mean age at onset was 61.29 (range: 37-86), and the mean follow-up was 20.3 months (range: 6-60). The most common findings at onset were seizures, observed in 10 patients (58.8%), which increased to 13 patients (76.5%) during follow-up, psychiatric symptoms in 35.3%, and hyponatremia in 35.3%. Ten patients required intensive care unit (ICU) admission, and 11 patients had an underlying malignancy, predominantly lung cancer. Additionally, one patient had CASPR2 antibodies, and another had AMPA-R antibodies. Lesion probability map analysis revealed predominant involvement of the bilateral mesiotemporal regions. Patients with a final modified Rankin Scale Score greater than 2 (n = 10) exhibited a higher prevalence of psychiatric symptoms, ICU admission, and hyponatremia. Of the 12 patients on anti-seizure medications, only 8 achieved seizure-free status during follow-up. Those with a paraneoplastic etiology were more likely to present with psychiatric symptoms. Mortality, which occurred in 7 patients, was associated with persistent seizures (4/4 vs 3/10; p = 0.015) and ICU admission (7/7 vs 3/10 p = 0.010) Patients with both serum and CSF antibody positivity showed trends towards exhibiting higher rates of lung cancer and mortality. Discussion: Male gender and seizures are common in GABAB-R encephalitis, which also displays high malignancy and mortality rates. Remarkable prognostic factors include psychiatric symptoms, seizures, malignancy, and hyponatremia. 4(23%) of 17 patients with GABA-B receptor antibody encephalitis experience persistent seizures during follow-up.