What Causes Bell’s Palsy?

Reviewed on 12/21/2020

What is Bell’s palsy?

Bell's palsy, the most common form of facial paralysis, is caused by swelling of the seventh cranial nerve as it passes through a narrow, bony passage.
Bell’s palsy, the most common form of facial paralysis, is caused by swelling of the seventh cranial nerve as it passes through a narrow, bony passage.

Bell’s palsy, the most common form of facial paralysis, begins with inflammation of a facial nerve. It causes drooping on one side of the face. Symptoms may improve in around two weeks, but it may take months for them to disappear. In a few cases, some symptoms don’t go away. 

Bell’s palsy is named for a Scottish surgeon, Sir Charles Bell, who showed that damage to the seventh cranial nerve caused facial paralysis. 

The condition goes by several other names, including acute peripheral facial palsy of unknown cause. Here are some other facts about Bell's palsy:

  • It usually occurs between the ages of 15 and 45.
  • It's more common in winter.
  • It's three times more likely to occur in a woman who is pregnant than one who is not.
  • In pregnant women, it usually occurs in the last trimester.
  • The average general practitioner will see one case every two years.

Bell’s palsy is unusual enough to be listed in databases of rare diseases. 

Signs of Bell's palsy

The symptoms of Bell's palsy include:

Facial paralysis

The primary symptom is partial to complete paralysis of one side of the face. The paralysis usually causes an observable drooping of that side of the face. It can be difficult or impossible to close the eye on that side of the face.

Impact on ear and hearing

During onset, Bell's palsy often causes sharp pain in the ear. Hypersensitivity to sound in the affected ear may follow.

Difficulty eating and speaking

The lack of nerve function around the mouth can make it difficult to say certain sounds. It can also make it difficult to eat. Food can get trapped in areas of the mouth. The sense of taste can also be affected. Excessive drooling may occur. 

Eye difficulties

Some of those with Bell's palsy cannot completely close the affected eye, even during sleep. This can cause the eye to be vulnerable to dryness, infection, and injury. Sometimes the eye produces excessive tears. 

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Causes of Bell’s Palsy

Bell's palsy is caused by swelling of the seventh cranial nerve as it passes through a narrow, bony passage. It presses on the bone, and the nerve loses function. 

Doctors don't know what causes the nerve to swell, but they believe that an existing but dormant viral infection could be to blame. They suspect a number of viruses, including the ones that cause chickenpox, mononucleosis, cold sores, measles, mumps, and flu

Stresses to the immune system, such as loss of sleep or trauma, could also play a role. 

When to see the doctor for Bell’s palsy

It's important to get an accurate diagnosis of Bell's palsy right away. The symptoms of Bell's palsy can resemble stroke, which needs prompt treatment. Also, steroid treatment of Bell’s palsy needs to begin quickly to be effective. 

Of course, a sudden loss of function on one side of the face can be highly distressing to patients, and a prompt diagnosis may calm their fears.

Diagnosis of Bell’s palsy

There are no specific tests for Bell’s palsy, but doctors can often diagnose it from a simple physical examination. Doctors usually want to be sure that they aren’t missing a more serious disorder, such as tumor or stroke. They may order tests to rule out other conditions. A test called electromyography can show the extent of the nerve damage. 

Treating Bell's palsy

Most people who have Bell's palsy begin to recover within three weeks. A few people will be left with slight weakness in the affected side of the face.

Recovery usually occurs with a minimum of medical intervention, but some treatments may be helpful, including these:

Steroids

Steroids given in the first 72 hours of symptoms may relieve the swelling and allow the nerve to recover. If steroid therapy is not started in the first 72 hours, it may not be helpful. Doctors usually prescribe a 10-day course of prednisolone. Even with timely steroid treatment, some patients may not recover completely.

Antivirals

Experts are unsure whether antiviral medication is helpful in treating Bell's palsy.  Doctors sometimes give valacyclovir or acyclovir in combination with steroids, especially if the case is severe.

Eye Care

When the eye doesn't close properly, it may get infected or injured. Patients can protect their eyes by wearing glasses or goggles during the daytime and an eyepatch at night. Lubricating drops will ease dry eyes.

Non-Drug Therapy

Doctors sometimes prescribe physical therapy for Bell's palsy. Massaging and exercising the muscles of the face could help with recovery, but evidence is inconclusive. There is similarly little evidence for acupuncture, heat therapy, electrical stimulation or similar measures.

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References
Australian Prescriber: "Management of Bell's palsy."

Clinical Medical Journal: "The impact of misdiagnosing Bell’s palsy as acute stroke."

Facial Palsy UK: "Bell's Palsy."

Facial Palsy UK: "Steroids, Antivirals and Antibiotics."

Johns Hopkins: "Bell's Palsy."

Mayo Clinic: "Bell's palsy."

National Institute of Neurological Disorders and Stroke: "Bell's Palsy Fact Sheet."

National Organization for Rare Disorders: "Rare Disease List."

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