64-year-old man is brought to the emergency department due to sudden onset of painless lower extremity weakness. He was swimming in a pool when he suddenly felt his legs become weak and had to struggle to exit the pool. The patient has had no loss of consciousness or visual or speech problems, but he is unable to pass urine. He also has had back pain for the last 2 months. Medical history is significant for type 2 diabetes mellitus, hypertension, and osteoarthritis. Physical examination shows significant motor weakness in both legs and numbness from the umbilicus to the soles of the feet He has no sensation in the perinea! area. Rectal tone is absent A urinary catheter is placed, and 800 ml of urine is collected.