Bell's Palsy


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.

Keywords: Bell's palsy; facial neuropathy; prednisolone; herpes simplex virus; seventh cranial neuropathy; synkinesis

Figure 1.

Diagram of the cerebral innervation of the facial muscles. Neurons for the lower face muscles arise from the opposite cerebral hemisphere, cross over in the pons, and synapse with facial nucleus neurons which will directly innervate lower facial muscles. Neurons for upper face (forehead) muscles arise from both cerebral hemispheres, and synapse in the same facial nucleus of the pons with facial motor neurons which then go to the upper facial muscles. Damage that affects one cerebral hemisphere, but not the other, such as from a stroke, will therefore cause weakness of the opposite lower facial muscles only, as the upper facial muscles will have intact innervation from the normal, same side, cerebral hemisphere. Adapted from Hathout GM (2008) Clinical Neuroradiology: A Case‐Based Approach. Cambridge UK: Cambridge University Press..


Further Reading

De Almeida JR, Khabori MA, Guyatt GH et al. (2009) Combined corticosteroid and antiviral treatment for Bell palsy. Journal of the American Medical Association 302: 985–993.

Gilchrist JM (2009) Seventh Cranial Neuropathy. Seminars in Neurology 25: 9–13.

Gilden DH (2004) Bell's palsy. New England Journal of Medicine 351: 1323–1331.

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How to Cite close
Gilchrist, James M(Mar 2010) Bell's Palsy. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0022323]