An 85-year-old woman presented to hospital in March 2012 for evaluation of left leg weakness. On the day of admission she had noticed weakness and clumsiness in the left leg that had come on over several hours and had worsened to the point that she was unable to walk. The leg felt numb and heavy. There were no symptoms in the right leg or upper limbs, no back pain and no sphincter disturbance. Several years previously, she had developed shingles affecting a mid-cervical dermatome, complicated by segmental muscle weakness that had slowly improved with time. Her health was otherwise good and she was physically active.

General medical examination, cranial nerves and upper limbs were normal. In the lower limbs there was no spasticity but she had severe left leg weakness in a pyramidal distribution. Power in the right leg was normal. The left plantar response was extensor. There was impairment to pinprick and temperature sensation in the right leg up to a level just above the costal margin. Vibration and joint position sense were normal. She could not walk. Emergency department staff arranged for routine blood tests, an ECG and a CT scan of head, all of which were normal. A bladder scan showed no urinary retention.