Clinical characteristics and prognostic clinical factors of anti-gamma-aminobutyric acid-B receptor (GABAB-R) encephalitis in Türkiye: a multicenter study

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.
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.
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.
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.

Male gender and persistent seizures are common features of GABAB-R encephalitis.
GABAB-R encephalitis is highly paraneoplastic and is most commonly associated with lung cancer.
Notable prognostic factors include psychiatric symptoms, hyponatremia at presentation, drug-resistant seizures, and the presence of malignancy.
A subgroup characterized by the presence of only serum GABABR antibodies tends to have a more benign course with limited clinical manifestations and better treatment responsiveness.
Patients with both serum and CSF antibody positivity showed trends towards exhibiting higher rates of lung cancer and mortality.

Male gender and persistent seizures are common features of GABAB-R encephalitis.
GABAB-R encephalitis is highly paraneoplastic and is most commonly associated with lung cancer.
Notable prognostic factors include psychiatric symptoms, hyponatremia at presentation, drug-resistant seizures, and the presence of malignancy.
A subgroup characterized by the presence of only serum GABABR antibodies tends to have a more benign course with limited clinical manifestations and better treatment responsiveness.
Patients with both serum and CSF antibody positivity showed trends towards exhibiting higher rates of lung cancer and mortality.