Beyond the Classic Triad: A Case of GQ1b Antibody-Positive Bickerstaff Brainstem Encephalitis Overlap Syndrome.

Anti-GQ1b antibody syndrome encompasses related postinfectious neurologic disorders, including Miller Fisher syndrome, Guillain-Barré syndrome, and Bickerstaff brainstem encephalitis. Recognizing overlap among these phenotypes can be difficult in the intensive care unit because profound unresponsiveness and loss of brainstem reflexes may be attributed to sedation or structural brain injury. A middle-aged man developed perioral numbness, blurred vision, ataxia, extremity paresthesias, and facial weakness after an upper respiratory infection. His condition progressed rapidly to respiratory failure, autonomic instability, generalized areflexia, and prolonged coma-like unresponsiveness. Brain imaging remained unrevealing. Cerebrospinal fluid showed albuminocytologic dissociation, and serum testing was positive for anti-GQ1b antibodies. He received intravenous immunoglobulin and intensive supportive care. Ocular and distal motor responses later returned, followed by resolution of the coma-like state, although ventilatory support was still required at transfer. This case demonstrates that severe anti-GQ1b overlap can produce profound but potentially reversible neurologic dysfunction and supports cautious neuroprognostication while the diagnostic evaluation is ongoing.