Bell's Palsy (Idiopathic Facial Paralysis)

What is Bell's Palsy?
Statistics on Bell's Palsy
Risk Factors for Bell's Palsy
Progression of Bell's Palsy
Symptoms of Bell's Palsy
Clinical Examination of Bell's Palsy
How is Bell's Palsy Diagnosed?
Prognosis of Bell's Palsy
How is Bell's Palsy Treated?
Bell's Palsy References

What is Bell's Palsy?

Bell's palsy is paralysis of the facial nerve of unknown cause. The diagnosis is made when in the typical clinical presentation no other cause can be identified.

Sir Charles Bell described the anatomy and physiology of the facial nerve in the 1800s. The facial nerve is a mixed nerve, containing:

Motor output fibres to the facial muscles (which control movement of muscles of the face);
Parasympathetic fibres to the lacrimal, submandibular, and sublingual salivary glands (which control tearing and salivation);
Afferent fibres for taste from the anterior two thirds of the tongue (which control taste of the front part of the tongue);
Somatic afferents from the external auditory canal and pinna (which control the outer ear).

These functions may be affected in Bell's palsy. The exact cause of Bell's is unknown, although viral (especially herpes simplex virus), inflammatory, autoimmune, and ischaemic (lack of blood supply) factors have been suggested. There is inflammation and swelling of the facial nerve where it travels through the bones of the skull.

Bell's palsy photo

Statistics on Bell's Palsy

The occurence rate per year is between 13 and 34 cases per 100,000 population. It appears to occur worldwide, equally in all races and both genders. However, an increased risk in the third trimester of pregnancy and the first week after delivery has been noted. Peak ages are 15-45 years but it also occurs in elderly people. Bell's palsy is rare in children.

Risk Factors for Bell's Palsy

The exact cause of Bell's palsy is not known. It is thought to be caused by viral infection, for example Herpes simplex virus, herpes zoster virus, mumps, HIV, etc. It is more common in adults, diabetics (5 times associated risk), and pregnant women (3 times associated risk).

Progression of Bell's Palsy

Bell's palsy will usually begin to improve by itself within days to weeks after onset. Approximately 60-80% of cases will recover completely although this may take 6-12 months. 8-10% of patients may have another episode of Bell's, either on the same side or opposite side of the face. If this happens, alternative causes should be excluded such as diabetes, tumours or infection.

Symptoms of Bell's Palsy

Many patients who present to the Emergency Department with Bell's palsy suspect they have suffered a stroke. They frequently complain of sudden paralysis and/or weakness on one side of their face. Symptoms can include:

Pain: Behind or in front of ear. May precede weakness of facial muscles by 1-2 days;
Loss of taste;
Sensitivity to sound (hyperacusis) on the affected side;
Headache;
Blurred vision;
Tingling or numbness of the cheek/mouth.

Clinical Examination of Bell's Palsy

Definable causes of facial paralysis must be ruled out by a thorough examination of the ears, nose, throat, and cranial nerves Examination findings can include:

Change in facial appearance:
- Facial droop, sagging of eyebrow;
- Difficulty with facial expressions, grimacing;
Facial paralysis of one side of the face
- Difficulty closing one eye;
- Difficulty with fine facial movements;
- Drawing of mouth to the non-affected side;
Drooling due to inability to control facial muscles;
Difficulty with eating and drinkingl
Dry eye secondary to being unable to close eye properly because of facial weakness.

How is Bell's Palsy Diagnosed?

Tests which may be done include:

Tests for viruses which might be the causative organism;
Spinal fluid analysis;
MRI scans of the head;
Hearing tests to assess the status of the hearing (auditory) nerve which travels with the facial nerve.

Electrical tests

During this test, the nerve is stimulated by an electrical current applied to the skin overlying the nerve. Function is graded by the amount of current required to cause excitation of the nerve and contraction of the facial muscles. This test is often repeated several times to determine extent of injury and progression of the disease. For example, if testing indicates equal muscle response on both sides of the face, the patient can be expected to have complete return of facial function in 3-6 weeks without significant deformity.

Prognosis of Bell's Palsy

The outcome of Bell's palsy varies. 80-90% of patients will make a gradual recovery although this may take up to 12 months to be complete. A small number of cases result in a permanent facial weakness.

How is Bell's Palsy Treated?

In many cases, no treatment is necessary. The goal of any treatment given in Bell's plasy is to relieve the symptoms. Corticosteroids or antiviral medications may reduce swelling and relieve pressure on the facial nerve. These drugs need to be given early on in order to be most effective(preferably within 24 hours of the onset of paralysis). The definite efficacy and benefit of these drugs are still under research.

Lubricating eye drops or eye ointments may be recommended to protect the eye if it cannot be closed completely. The eye may need to be patched during sleep to protect it.

Surgical procedures to decompress the facial nerve have not been shown to routinely benefit people with Bell's palsy.

Bell's Palsy References

Allen D, Dunn L. Aciclovir or valaciclovir for Bell's palsy (idiopathic facial paralysis). Cochrane Database Syst Rev. 2004;(3):CD001869. [Abstract | Full text]
Baringer JR. Herpes simplex virus and Bell palsy. Ann Intern Med. 1996;124(1 Pt 1):63-5. [Abstract]
Bell C. An Exposition of the Natural System of the Nerves of the Human Body. London: Royal Society; 1824. [Book]
Bell C. The Nervous System of the Human Body. London: Longman; 1830. [Book]
Hilsinger RL Jr, Adour KK, Doty HE. Idiopathic facial paralysis, pregnancy, and the menstrual cycle. Ann Otol Rhinol Laryngol. 1975;84(4 Pt 1):433-42. [Abstract]
Lambert M. Bell palsy [online]. Omaha, NE: eMedicine; 2005 [cited 3 January 2006]. Available from: URL link
Liston SL, Kleid MS. Histopathology of Bell's palsy. Laryngoscope. 1989;99(1):23-6. [Abstract]
May M. The Facial Nerve. New York, NY: Thieme; 1986. [Book]
Monnell K, Zachariah SB. Bell palsy [online]. Omaha, NE; eMedicine; 2005 [cited 3 January 2006]. Available from: URL link
Mountain RE, Murray JA, Quaba A, Maynard C. The Edinburgh facial palsy clinic: A review of three years' activity. J R Coll Surg Edinb. 1994;39(5):275-9. [Abstract]
Peitersen E. Bell's palsy: The spontaneous course of 2,500 peripheral facial nerve palsies of different etiologies. Acta Otolaryngol Suppl. 2002;(549):4-30. [Abstract]
Peitersen E. The natural history of Bell's palsy. Am J Otol. 1982;4(2):107-11.
Salinas RA, Alvarez G, Alvarez MI, Ferreira J. Corticosteroids for Bell's palsy (idiopathic facial paralysis). Cochrane Database Syst Rev. 2002;(1):CD001942. [Abstract | Full text]
Schirm J, Mulkens PS. Bell's palsy and herpes simplex virus. APMIS. 1997;105(11):815-23. [Abstract]
Ronthal M. Bell's palsy [online]. Waltham, MA: UpToDate; 2005 [cited 3 January 2006]. Available from: URL link