Motor Neuron Disease with Guillain-Barré Syndrome? Motor Band Sign with Anti-GQ1b Antibodies

A 79-year-old former marathoner, with memory impairment since age 78, developed increasing stumbling and progressively worsening waddling gait. Three months after gait disturbance onset, she noted mild dysphagia. With declining walking distance and endurance, she presented to our hospital six months after onset, exhibiting frontal signs, Parkinsonism with marked trunk rigidity, and hyperreflexia of the jaw and limbs. L-dopa challenge tests showed no improvement. At seven months post-onset, she had difficulty rising. By nine months, she relied on a walker, and speech disturbance appeared. At 10-11 months, both dysarthria and dysphagia rapidly worsened, she became bed-ridden, and upper limb weakness developed (though she could still use chopsticks). Neurological examination at one year revealed severe dysarthria/dysphagia, four extremity fasciculations and muscle weakness (grade 2 in upper limbs, grade 1 in lower limbs), trunk-dominant rigidity, and hyperreflexia in the jaw and limbs. Brain MRI, specifically susceptibility-weighted imaging, revealed motor band signs. Cerebrospinal fluid study revealed albuminocytological dissociation. Needle electromyography revealed acute denervation and chronic reinnervation in the cranial nerve, cervical, and lumbar areas, which was suggestive of motor neuron disease (MND). Serum anti-GQ1b antibodies were detected. Immunotherapy was followed by mild improvement, which might suggest a reversible component, although definitive pathological overlap remains unconfirmed. This case highlights a diagnostic challenge where an acute immune-mediated neuropathy could potentially be superimposed on a chronic neurodegenerative process. Anti-GQ1b antibodies should be interpreted with caution, as they may reflect either a true clinicopathological overlap with Guillain-Barré syndrome or a secondary phenomenon (epiphenomenon) related to the primary neurodegenerative process.