Facial Nerve Problems (cont.)
How are the causes of facial nerve dysfunction diagnosed?
Causes of facial nerve disorder vary from unknown to life threatening.
Sometimes, there is a specific treatment for the problem. Accordingly, it is
important to investigate why the problem has occurred. The specific tests used
for diagnosis will vary from patient to patient, but include:
- Hearing tests: Hearing tests are done to assess the
status of the auditory nerve. The stapedial reflex test can evaluate the branch of the facial nerve
that supplies motor fibers to one of the muscles in the middle ear.
- Balance tests: Will help find out if part of the auditory nerve is involved.
- Tear tests: The loss of the ability to form tears may help to locate the
site and severity of a facial nerve
lesion.
- Taste tests: The loss of taste in the front of the
tongue may help locate
the site and severity of a facial nerve lesion.
- Salivation test: Decreased flow
of saliva may help locate the site and severity of a facial nerve lesion.
- Imaging studies: help determine if there is
infection, a tumor, a bone fracture, or any other abnormality. These studies are
usually a CT scan and/or a
MRI scan.
- Electrical tests: Stimulation of the nerve by an
electrical current tests whether the nerve can still cause muscles to contract.
It can be used to evaluate progression of the disease. For example, if testing
indicates equal muscle response on both sides of the face, the patient can be expected to have
complete return of facial function in three to six weeks without significant deformity.
What is Bell's palsy?
Bell's palsy is paralysis of the facial nerve of unknown cause. The diagnosis
is made when no other cause can be identified. Bell's palsy is thought to be
caused by a viral infection of the facial nerve. The most likely virus is the herpes simplex
virus. Other names for this condition are "idiopathic facial
palsy" or Antoni's palsy.
Bell's palsy is usually a self-limiting, non-life
threatening condition that spontaneously remits within six weeks. The incidence is 15-40 new cases per
100,000 people per year. There is no predominant age or racial predilection;
however it is 3.3 times more common during pregnancy and slightly more common in
menstruating females. In general, the incidence increases with advancing age.
The typical symptoms of Bell's palsy include:
- Unilateral acute paralysis of facial muscles. The paralysis involves all
muscles, including the forehead.
- About half the time, there is numbness or pain in the ear, face, neck or
tongue.
- There is a preceding viral illness in 60% of patients.
- There is a family history of Bell's palsy in 10% of patients.
- Less than 1% of patients have bilateral problems.
- There may be a change in hearing sensitivity (often increased sensitivity).
The proposed mechanism of injury of the facial nerve in Bell's palsy is:
- Primary viral infection (herpes) sometime in the past.
- The virus lives in the nerve (trigeminal ganglion) from months to years.
- The virus becomes reactivated at a later date.
- The virus reproduces and travels along the nerve.
- The virus infects the cells surrounding the nerve
(Schwann cells) resulting in inflammation.
- There immune system responds to the damaged Schwann cells which and causes
inflammation of the nerve and subsequent weakness or paralysis of the face.
- The course of the paralysis and the recovery will depend upon the degree
and amount of damage to the nerve.
Next: What are treatment options of facial nerve paralysis? »
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