The facial nerve controls facial expression as well as eye closure and lip movement. Bell's palsy describes a weakness of the facial nerve. Although people use it to refer to any facial nerve weakness, the term technically only refers to cases where the cause of the weakness is not known. Lyme disease can also cause facial nerve weakness or paralysis. According to the journal Clinical Pediatrics, in areas where Lyme disease occurs, it is actually the leading cause of facial paralysis. Both Bell's palsy and Lyme disease usually cause weakness on only one side and it is usually temporary.
Asymmetrical Smile
Because the facial nerve controls the muscles in the face, weakness of that nerve impairs normal facial muscle movement. When Bell's palsy or Lyme disease only affects the facial nerve on one side, the face loses its symmetry. An asymmetrical smile is one of the first things that people with either of the two conditions notice, as that is a feature that has an important affect on their social interaction.
Vision Loss
While the opening of the eyes is controlled by a different nerve, the facial nerve is responsible for eye closure. If Bell's palsy or Lyme disease is severe enough, the condition can lead to incomplete eye closure. Although not as noticeable as a lopsided smile, this is actually a very dangerous feature of either type of facial weakness. The consequence of being unable to close the eye is that the cornea can become dry and damaged, potentially leading to vision loss. People with facial nerve weakness need to use lubricating eye drops and possibly tape their eye shut at night to prevent dryness.
Drooling
The facial nerve controls the muscles responsible for lip movement. Therefore, Bell's palsy or Lyme disease can cause an inability to move the lips on the affected side. The corner of the mouth on that side typically starts to sag and cannot close completely. That incomplete closure can lead to leakage of saliva or food, which can look to others as if the person is drooling.
Loss of Muscle
People with long-term facial nerve paralysis from Bell's palsy or Lyme disease can lose facial muscle bulk due to lack of use. After a prolonged time of inactivity, the muscles of the face start to atrophy. That can make the face appear even more uneven, which becomes noticeable even at rest.
References
- Clinical Pediatrics; Facial nerve palsy in the pediatric population; Josef Shargorodsky; May 2010
- British Medical Journal; Lyme disease in facial palsy: differentiation from Bell's Palsy; David Markby; January 1989
- Cleveland Clinic Journal of Medicine; When is facial paralysis Bell palsy? Current diagnosis and treatment; Anwar Ahmed; May 2005
