To investigate the clinical and diagnostic characteristics of autoimmune encephalitis (AE) double-positive for anti-γ-aminobutyric acid type B receptor (GABA_BR) and anti-metabotropic glutamate receptor 2 (mGluR2) antibodies.

A retrospective analysis was performed on the clinical data of a patient who was initially admitted to the Department of Neurology at the First Affiliated Hospital of Harbin Medical University in January 2025 and was readmitted in March 2025 due to symptom exacerbation, where a diagnosis of AE double-positive for anti-GABA_BR and anti-mGluR2 antibodies was confirmed via serological and CSF testing. Relevant literature was also reviewed to explore the clinical features of this condition.

A 54-year-old female patient presented with epileptic seizures as the initial symptom, and subsequently developed psychiatric and behavioral abnormalities, visual hallucinations, cognitive decline, and sleep disorders during the disease course, consistent with limbic encephalitis syndrome. Brain MRI showed bilateral hippocampal long T₂ signals. Anti-GABA_BR antibodies were positive in both serum and CSF, with titers of 1∶1 000 and 1∶10, respectively. Anti-mGluR2 antibodies were positive in CSF at a titer of 1∶1 but negative in serum. Systemic oncological screening revealed no definitive malignant lesions; however, serum tumor markers showed mild elevations in neuron-specific enolase (17.18 μg/L) and carbohydrate antigen 72-4 (28.79 U/mL). Symptoms improved significantly after treatment with glucocorticoids combined with plasma exchange and mycophenolate mofetil.

AE with double positivity for anti-GABA_BR and anti-mGluR2 antibodies is extremely rare. Early comprehensive antibody testing and immunotherapy may help improve short-term prognosis, and long-term follow-up is warranted to exclude a potential paraneoplastic etiology. The clinical significance of anti-mGluR2 antibodies needs further investigation.