Bell’s palsy, also known as facial palsy, is the sudden onset of paralysis of one of the facial nerves. The main symptom is muscle weakness on one side of the face, causing the face to droop. The left and right sides of the face are affected with equal frequency. It is rare for both sides to be affected at the same time.
Bell’s palsy can affect anyone. Its annual incidence is 2 to 3 people per 10 000 of the population, and this is thought to be similar across all ethnic groups. Men and women are affected equally; however pregnant women and people with diabetes have an increased risk. Bell’s palsy occurs most often between the ages of 10 and 40 years.
Signs and symptoms
Bell's palsy is named after the Scottish physician, Sir Charles Bell, who first described the condition in 1830.
Often the first symptom of Bell's palsy is a dull, aching pain behind or in the ear. This can be present for a day or two before facial weakness is noticed. While the involved side of the face may feel numb, it is still possible to feel if it is touched.
Developing over several hours or up to two or three days, signs and symptoms can range in severity and include:
- Asymmetrical (crooked) smile
- Inability to close the eye on the affected side
- Reduced sensation on the affected side
- Impaired taste
- Slurring of words
- Difficulty eating
- Muscle weakness on the affected side, including the muscles of the eyelids and forehead
- Reduced tear production on the affected side
- Increased sensitivity of hearing in the affected ear.
Originating from the base of the brain are twelve pairs of nerves called the cranial nerves, which are named and numbered. They are responsible for a variety of specialised functions such as smell, equilibrium (balance), pupil contraction and hearing. The seventh cranial nerves are the facial nerves that are involved in eyelid closure, facial expression, saliva and tear production, and the sensation of taste at the front of the tongue.
Bell’s palsy is thought to occur when facial nerves become compressed or inflamed. Part of the nerve is encased within a bony canal and is therefore susceptible to compression when swollen. Although not fully understood, the swelling is thought to occur as the result of a viral infection of the facial nerve. The herpes simplex virus, which causes cold sores, is one virus thought to be responsible for the condition.
Other factors linked to the development of facial nerve paralysis include ear infections, tumours, brain injury and several viruses including herpes zoster (the virus that causes chickenpox and shingles) and Epstein-Barr virus (the virus that causes glandular fever). These conditions do not cause Bell’s palsy, but they can produce very similar symptoms. Bell's palsy is differentiated from these conditions by the fact that its cause remains unknown.
Bell's palsy is strongly suggested by its characteristic symptoms. It is not a life-threatening condition but it can produce symptoms similar to other more serious causes for facial paralysis, such as a stroke or tumour. For this reason, other possible causes for the symptoms must be excluded before a definitive diagnosis of Bell's palsy can be made. In order to confirm the diagnosis the doctor may undertake the following:
- A full medical history, including any recent illnesses or viral infections
- Discussion of current symptoms
- A complete physical and neurological assessment eg: sensation in the face, the strength of the facial muscles.
To assist further with the diagnosis and to rule out other conditions, the doctor may recommend:
- Blood tests
- Hearing tests
- Balance tests
- Taste and salivation tests
- Tear test (to measure the eye’s ability to produce tears)
- Computerised tomography (CT) or magnetic resonance imaging (MRI)
- Electrical tests (electromyography) to measure the functioning of the nerve.
While there is no specific cure for Bell’s palsy, treatment focuses on improving facial nerve function, minimising nerve damage and protecting the affected eye. The treatment used will depend upon the apparent cause and severity of the condition.
Corticosteroid medications, such as prednisone, are often given to help reduce inflammation in the nerve. These are most effective when given early in the course of the condition. Some medical research has shown that antiviral medications such as aciclovir, or a combination of a corticosteroid and an antiviral medication may also help to speed recovery. However, the role of antiviral medications in Bell's palsy remains unclear.
The eye needs to be protected and kept moist in order to prevent damage to the cornea (the lining of the eye). This will usually involve the use of artificial tears to lubricate the eye. Taping the eye shut overnight may also be suggested.
Surgery to relieve compression of the facial nerve may be considered in severe, prolonged cases. However, this kind of surgery is used rarely as it carries a high risk of nerve damage. Other types of surgery that may be considered in some instances include:
- Nerve repair or nerve grafts
- Muscle transposition - moving a working muscle from the temple area to supply movement to the paralysed part of the face
- Muscle transfer - using a muscle from the leg to supply muscle bulk and function to the paralysed part of the face
- Eyelid procedures - such as eyelid repositioning, eyelid lifts, or the insertion of a specialised stitch to prevent the lower eyelid from drooping
- Alternative treatments such as massage, acupuncture and chiropractic manipulation may prove helpful in some cases
In up to 90% of cases, complete recovery is achieved within six to 12 weeks of the symptoms first appearing. In a small percentage of cases symptoms may never completely disappear and some degree of facial paralysis remains permanently. Those aged 60 years or more have a lower likelihood of complete recovery and a higher risk of permanent paralysis. Bell's palsy can recur, with estimates of recurrence rates ranging from 4 to 14% of cases.
Mayo Clinic (2014). Bell’s palsy (Web Page). Rochester, NY: Mayo Foundation for Medical Education and Research. http://www.mayoclinic.org/diseases-conditions/bells-palsy/basics/definition/CON-20020529 [Accessed: 26/03/17]
Taylor, D.C. (2015). Facial nerve problems and Bell's palsy (Bell Palsy) [Web Page]. MedicineNet.Com. San Clemente, Ca: MedicineNet, Inc. www.medicinenet.com/facial_nerve_problems/article.htm [Accessed: 26/03/17]
Taylor, D.C. (2016). Bell palsy (Web Page). Medscape Reference: Drugs, Disease & Procedures. New York: WebMD LLC. http://emedicine.medscape.com/article/1146903 [Accessed: 26/03/17]