Bell's palsy

Definition

Bell's palsy is a disorder caused by damage to cranial nerve VII, involving sudden facial drooping and decreased ability to move the face.

Causes, incidence, and risk factors

Bell's palsy is an acute form of cranial mononeuropathy VII, and it is the most common form of this type of nerve damage (peripheral neuropathy). Statistics indicate that the disorder affects approximately 2 in 10,000 people. However, the actual incidence is likely to be much higher (around 1 in 500 to 1 in 1,000).

The disorder is a mononeuropathy (involvement of a single nerve) that damages the seventh cranial (facial) nerve, the nerve that controls movement of the muscles of the face. The cause is often not clear, although herpes infections may be involved.

The disorder is presumed to be associated with inflammation of the facial nerve where it travels through the bones of the skull. Other causes of cranial mononeuropathy VII, such as head injury and tumor, need to be excluded. Other conditions, such as sarcoidosis, diabetes, and Lyme disease, are associated with Bell's palsy.

Symptoms

• Pain
  • Behind ear
  • In front of ear
  • May precede weakness of facial muscles by 1-2 days
• Loss of sense of taste
• Sensitivity to sound (hyperacusis) on the affected side
• Headache
• Face feels stiff
• Face feels pulled to one side
• Difficulty with eating and drinking
• Change in facial appearance
  • Facial droop
  • Difficulty with facial expressions, grimacing
• Facial paralysis of one side of the face
  • Difficulty closing one eye
  • Difficulty with fine facial movements
• Drooling due to inability to control facial muscles
• Dry eye secondary to being unable to close eye properly because of facial weakness

Signs and tests

Examination shows upper and lower facial weakness, which is almost always isolated to one side of the face or occasionally to the forehead, eyelid, or mouth. Despite a patient reporting feeling sensory symptoms, the loss of sensation on examination is a rare and disturbing finding. Blood pressure is normal. If there are no other abnormalities on examination, no imaging studies are usually done.

Blood tests for sarcoidosis or Lyme disease may be considered under some circumstances. If there is no improvement in the facial paralysis after several weeks, an MRI is done to rule out other causes of the dysfunction. An EMG and nerve conduction studies may also be done to determine the severity of nerve damage.

Treatment

In many cases, no treatment is necessary. The goal of treatment is to relieve the symptoms.

Corticosteroids or antiviral medications may reduce swelling and relieve pressure on the facial nerve. These drugs must be given early to be most effective (preferably within 24 hours of the onset of paralysis).

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.

Expectations (prognosis)

The outcome varies. Approximately 60% to 80% of cases resolve completely within a few weeks to months. Some cases result in permanent changes. The disorder is not a threat to life.

Complications

• Disfigurement from loss of facial movement
• Damage to the eye (corneal ulcers and infections)
• Chronic spasm of face muscles or eyelids
• Chronic taste abnormalities
• Synkinesis (abnormality in re-innervation of muscles resulting in tears when laughing or inappropriate salivation)

Calling your health care provider

Call for an appointment with your health care provider if facial drooping or other symptoms of Bell's palsy occur. Only a trained health care provider can discriminate Bell's palsy from other, more serious conditions, such as stroke. If you develop signs of Bell's palsy, call your health care provider immediately so that a stroke can be ruled out as quickly as possible.

Prevention

Use of safety measures may reduce the incidence of head injury. Many of the other factors associated with this disorder are not readily preventable.

Illustrations

Ptosis, drooping of the eyelid

Facial drooping

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