A 29-year-old female presents to A&E with a 3/52 Hx of progressive lower limb weakness and lower back pain. Prior to this, she had flu-like symptoms and also developed diarrhoea. Upon further questioning, she also complains of numbness and tingling sensations in her hands, which gradually ascended to her elbows. On examination, her cranial nerves are intact. The light touch, pinprick and vibration sensations are diminished in her upper limbs to the elbow and lower limbs to the hip bilaterally. Power is 3/5 in the ankle dorsiflexion bilaterally and 4/5 at hip flexors. Reflexes are absent and plantars are mute. Her BP is 130/80, HR 60, Sats 99% (RA). Her PMHx includes DMT1. What is the most likely diagnosis?