Anti-GABAB Receptor Autoimmune Encephalitis: A Report of a Rare Case in Central America

Autoimmune encephalitis (AE) is a rare disease. There have been very few reports of anti-GABAB receptor encephalitis, and no case of this subtype has ever been reported in Central America. We present a case of a 21-year-old male patient with an unremarkable previous medical history who was hospitalized because of a new onset of seizures and status epilepticus. Central nervous system infections, neoplastic disorders, cerebrovascular disease, septic and metabolic encephalopathy, and drug toxicity were ruled out. Cerebrospinal fluid (CSF) revealed lymphocytic pleocytosis and oligoclonal bands. Initial head computed tomography (CT) scans with and without contrast were normal, and brain magnetic resonance imaging (MRI) showed no abnormalities. An electroencephalogram showed slow waves and spike waves in the frontal and temporal areas. During hospitalization, encephalopathy progressed, along with seizures and altered mental status requiring mechanical ventilation and admission to the intensive care unit. Intravenous valproic acid and phenytoin for seizure control were given. The unexplained seizures, persisting altered mental status despite the reduction of sedatives, CSF pleocytosis, and oligoclonal bands, along with reasonable exclusion of alternative disorders, suggested AE. The diagnosis was confirmed with positive anti-GABAB1-B2 receptor antibody titers in serum and CSF. A whole-body CT scan showed increased pancreatic head size, but endoscopic ultrasonography ruled out malignancy, and a normal IgG4 range excluded IgG4 disease. The patient received treatment with methylprednisolone, plasmapheresis, and immunoglobulin therapy, with excellent response. The patient has been followed up for seven months, taking immunomodulation with mycophenolate. He is seizure-free with valproic acid and levetiracetam treatment and is receiving cognitive rehabilitation after mild cognitive decline was noted in the psychometric analysis.