A 69-year-old male presents with sudden onset weakness of his | Neurology collections 2020

A 69-year-old male presents with sudden onset weakness of his legs associated with urinary retention. Five
years previously he was diagnosed with sigmoid colonic carcinoma which was surgically resected.
Examination revealed a flaccid paraparesis of the legs with absent tendon reflexes and plantar responses.
Pinprick and temperature sensations were absent to T12 level, but there was a relative sparing of light touch

and joint position sensation.
What is the most likely diagnosis?