Bell’s Palsy, Pathophysiology, Symptoms, Diagnosis and Treatment, Animation

Bell’s palsy is a form of facial muscle weakness 
or paralysis, typically on one side of the   face. It results from dysfunction of the facial 
nerve, also known as the seventh cranial nerve.   The facial nerve has many branches 
and diverse functions. It controls   the muscles of facial expression, including 
those involved in eye blinking and closing;   it carries nerve impulses to tear glands, salivary 
glands; and conveys taste sensations from the   anterior two-thirds of the tongue. There are 
two facial nerves, one on each side of the face.   Typically, only one nerve, and hence 
one side of the face, is affected.  The malfunction of the facial nerve is 
thought to result from its inflammation.   The swollen nerve is compressed as it 
exits the skull within a narrow bony canal.  Symptoms develop suddenly, usually within a 
couple of days, and can range from mild weakness   to total paralysis of face muscles.

Other 
symptoms may include drooping of mouth, drooling,   inability to close one eye, facial pain or 
abnormal sensation, distorted sense of taste,   and intolerance to loud noise.
By definition, Bell’s palsy is idiopathic,   meaning it has no known cause, but it has 
been associated with certain viral infections.   In particular, reactivation of a dormant virus, 
triggered by stress, trauma or minor illness,   is often thought to be the culprit.
Risk factors include diabetes,   hypertension, obesity, pregnancy, 
and upper respiratory infections.  Diagnosis is based on clinical presentation 
after other possible causes of facial paralysis   are excluded. Patients usually present 
with rapid development of symptoms,   reaching a peak in severity around 
72 hours from the time of onset.   In most cases, muscle weakness can be observed 
with both upper and lower facial muscles,   including the forehead, eyelid, and mouth. 
If forehead muscle strength is not affected,   a central cause, especially 
stroke, should be suspected.   This is because the upper facial muscles, unlike 
the lower ones, receive nerve impulses from both   hemispheres of the brain, so a lesion in 
one side will not affect their function.  An electromyography test can be used to confirm 
nerve damage and determine the extent of severity.   Imaging studies can help rule out structural 
causes, such as a tumor or skull fracture.  Because Bell's palsy impairs the eyelid’s ability 
to close and blink, the affected eye is exposed   to drying and potential injury.

Patients must 
keep the eye moist with lubricating eye drops,   and protect it from injury with 
an eye patch, especially at night.  Without treatment, Bell’s palsy resolves 
spontaneously in about 2 thirds of patients.   Symptoms usually start to improve after a few 
weeks, and complete recovery is achieved in about   six months. Corticosteroids, when started early, 
can reduce inflammation and improve recovery.   Some patients may benefit from 
physical therapy or facial massage.   Decompression surgery to 
relieve pressure on the nerve is   rarely needed and not usually recommended. 
Severe cases may take longer to resolve.   A small number of patients with complete paralysis 
may continue to have some symptoms for life..

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