Neuromuscular Case Vignettes

68 year old woman with subacute general weakness and numbness

68 year old woman presented with severe non-radicular neck and back pain, and progressive weakness of the upper and lower limbs, to the extent that she was not able to walk or even sit unassisted, about 2 weeks after receiving a flu shot. She also developed tingling and numbness in her feet. The symptoms were progressively deteriorating over the next 3 weeks. Exam showed that the mental status and cranial nerves were normal. There was diffuse muscle atrophy in the hands an leg muscles, neck flexion and extension 5/5,  deltoid , biceps and triceps 4/5 distal hand  muscles 2-3/5.  Strength was 3/5 in lower limbs throughout. The reflexes were generally absent with flexor plantars.Sensory exam showed severe impairment of proprioception at the toes, ankles and in the fingers. Vibratory sensation was absent at the knee and elbows and pinprick sensation was to the proximal thighs and forearms.  The patient was not able to stand or walk.

What is the localization and differential diagnosis?