A 58-year-old female nurse with a background of asthma gave a 7-year history of slowly progressing ‘stiff knees’ and stumbles. A rheumatological diagnosis was suspected; however, bilateral lower-limb radiological investigations were normal. Her gait slowed to the extent that she had to take leave from work and required a walking stick. Subsequently, she developed gradual onset of altered sensation below the thorax with urinary incontinence and difficulty in passing stool. She therefore presented to the emergency department.

On examination, she had reduced strength of right ankle dorsiflexion and plantarflexion …