Case Report: Anti-GQ1b antibody-positive overlap syndrome: a pediatric case involving the brainstem, spinal cord, and peripheral nerves.

Disorders associated with anti-GQ1b antibodies predominantly encompass Bickerstaff brainstem encephalitis (BBE), Guillain-Barré syndrome (GBS), and Miller Fisher syndrome. Concurrent presentation of BBE, GBS, and acute transverse myelitis is exceptionally rare and presents significant diagnostic and therapeutic challenges. This report describes an 8-year-old boy who exhibited clinical features consistent with all three conditions, including impaired consciousness, ophthalmoplegia, ataxia, and limb weakness. Laboratory investigations revealed positive serum anti-GQ1b IgG antibodies, elevated cerebrospinal fluid protein levels with mild lymphocytic pleocytosis, and neurophysiological findings indicative of peripheral nerve demyelination. Magnetic resonance imaging of the brain and spinal cord demonstrated evidence of brainstem encephalitis and extensive spinal cord involvement. Following treatment with intravenous immunoglobulin and corticosteroid pulse therapy, marked neurological improvement was observed, and follow-up evaluations demonstrated favorable resolution of radiological abnormalities. This case highlights that anti-GQ1b antibody-associated syndrome may simultaneously affect the brainstem, spinal cord, and peripheral nerves. Early recognition and prompt initiation of combined immunotherapy may be critical for optimizing clinical outcomes.