A48-year-old woman with a history of type 1 diabetes mellitus and hyperlipidemia has had gradually progressive numbness, tingling, and gait difficulties for the past 12 months. she first noticed numbness and tingling in her hands, followed by thigh stiffness, numbness in the feet and calves, and most recently gait instability. she has no history of neurologic symptoms. examination reveals no electrical sensation radiating down her spine with neck flexion, as well as normal mental status and cranial nerve function, including funduscopic examination. manual muscle testing demonstrates normal extremity power, bulk, and tone, but slight proximal lower extremity weakness with minimally increased tone in her feet. there are bilateral hoffmann signs, sustained clonus of the right ankle, and three beats of clonus on the left, with extensor plantar responses bilaterally. she has no joint proprioception in the ankles and toes, with mildly reduced touch and severely reduced vibration; she also has moderately reduced vibration in her fingers. her gait is ataxic and spastic with a positive romberg sign. an mri scan of the brain is unremarkable. what laboratory results would confirm the diagnosis?