Bell's palsy is an idiopathic neuropathy of the facial nerve, meaning there is no known cause. It was first described in the medical literature in 1821 and is the most common cause of facial neuropathy. It usually presents as acute, weakness of one side of the entire face. This is in contrast to facial weakness from a cerebral hemisphere stroke which spares the forehead muscles of the face. Increased loudness and decreased taste on the affected side are also common, as are numbness and pain. Loss of hearing, ringing in the ears, problems with speech or swallowing or weakness elsewhere should provoke looking for another diagnosis than Bell's palsy. The chance of full recovery is excellent but the use of steroids within three days of onset, especially in patients with moderate or severe weakness, improves the chance of full recovery even further. The use of antiviral agents should probably be limited to those patients with severe weakness, or with evidence of herpes zoster infection in the ear or mouth (Ramsay Hunt syndrome).

Key concepts

• Bell's palsy is the most common cause of facial neuropathy.
  
• It is defined as idiopathic facial neuropathy.
  
• It has as excellent prognosis, with 85% of patients having recovery by 6 months.
  
• Steroids given within 3 days of onset improve the chance of recovery even further.
  
• The facial nerve travels a long and bending path, which is why so many diseases can affect it.
  
• Facial neuropathy causes weakness of the entire side of the face versus cerebral hemisphere stroke which spares the forehead muscles.
  
• There is mounting evidence to support the hypothesis that Bell's palsy in most patients is caused by reactivation of herpes simplex virus in the geniculate ganglion.