Feature Article

Finding the cause of sudden leg weakness

Wai-Kuen Leong, Robert H Edis



Sudden weakness of the legs is a presenting symptom which requires urgent attention. ‘Sudden weakness’ not only refers to weakness that is acutely obvious over seconds, hours or days. In some cases, weakness may have been coming on over weeks, discounted by the patient, who then presents with ‘apparently sudden weakness’.

Key Points

  • ‘Sudden’ weakness can be interpreted to mean weakness that becomes obvious over seconds, hours, days or weeks.
  • Important diagnostic clues, such as localised spinal tenderness or an extensor plantar response, can be revealed during a brief physical examination.
  • A thorough neurological examination will also evaluate the appearance, tone, power and sensation of the face, neck, trunk, arms as well as the legs.
  • Rapid progression of weakness, ascending from legs to the arms and face, or leg weakness with back pain and urinary retention, are indications for urgent referral.
  • An acute lesion of the spinal cord may be accompanied by ‘spinal shock’ which may obscure the distinction between an upper and a lower motor neuron lesion.
  • Common causes of sudden leg weakness include drop attacks, the Guillain–Barr syndrome and nontraumatic spinal cord compression due to metastatic tumour or an epidural abscess.