Bell's palsy

Alternative names

Facial 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
  o Behind ear
  o In front of ear
  o 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
  o Facial droop
  o Difficulty with facial expressions, grimacing
  
• Facial paralysis of one side of the face
  o Difficulty closing one eye
  o 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.