A 9-year-old female with bilateral leg weakness after influenza vaccination.

A 9-year-old female developed bilateral leg weakness on the same day she received an influenza vaccination. Her condition had gradually worsened during the 5 months prior to her presentation. She had no family history of hereditary disease. Physical examination revealed muscle atrophy without fasciculation in all four limbs. Muscle power in the proximal and distal limbs was 3 of 5, and the deep tendon reflexes of the lower limbs were decreased bilaterally, but there was no sensory function impairment, urinary incontinence, or other autonomic nerve system dysfunction. Nerve conduction velocity test revealed axonal degeneration with demyelination in both upper and lower limbs. Lumbar puncture