A 59-year-old female pub landlady presents with acute, severe | Neurology collections 2020

A 59-year-old female pub landlady presents with acute, severe lumbar back pain.
There is no history of orthopaedic problems and until this event she had been in perfect health.
The patient complains of paraesthesia in the lower limbs and on further questioning has not voided urine since
the onset of the pain.
Neurological examination reveals weakness (3/5 of both lower limbs, loss of sensation in L4, L5 and S1).
Vibration sensation and joint position sensation is preserved. Reflexes in the ankles and knees are absent and
the plantar response is equivocal.
The blood pressure is 158/68 mmHg, heart rate 95 bpm, temperature 36.9°C and ECG shows normal sinus
rhythm with no ischaemic changes.
The remainder of the examination is normal.
Which of the following should be undertaken next for this patient?