Acute Bickerstaff Brainstem Encephalitis in a Middle-Aged Male: Diagnostic Challenges and Therapeutic Responses

Bickerstaff brainstem encephalitis (BBE) is a rare, post-infectious autoimmune disorder characterized by ophthalmoplegia, ataxia, and altered consciousness. It shares overlapping features with Guillain-Barré syndrome (GBS) and Miller Fisher syndrome (MFS), and diagnosis is often clinical, supported by anti-GQ1b antibodies. A 40-year-old previously healthy male presented with dizziness, diplopia, gait instability, and a recent viral prodrome. Neurologic examination revealed bilateral sixth cranial nerve (CN VI) palsy, partial involvement of the third cranial nerve (CN III), and bilateral dysmetria. Brain Imaging was unremarkable. Cerebrospinal fluid (CSF) analysis revealed lymphocytic pleocytosis, and the infectious workup was negative. Serum Anti-GQ1b antibody levels were elevated. The patient was treated with intravenous immunoglobulin (IVIG), resulting in marked improvement over four days; however, mild deficits persisted at the time of discharge to a rehabilitation facility. BBE remains a diagnostic challenge due to its rarity and nonspecific findings. Brain magnetic resonance imaging (MRI) may be normal, and anti-GQ1b antibodies, though not always present, are valuable for diagnosis. Prompt treatment with IVIG improves prognosis. This case exemplifies the clinical overlap within the Fisher-Bickerstaff spectrum and the importance of early recognition. Early identification of BBE is crucial for timely treatment and improved outcomes. This case underscores the need to consider autoimmune encephalitis in patients with acute brainstem symptoms and recent viral illness, even when imaging is normal.