What Causes Bell's Palsy?

Bell's palsy is facial paralysis due to nerve damage, often caused by a stroke.

Bell's palsy (also called idiopathic facial palsy) is a condition in which patients experience temporary facial paralysis or weakness on one side of the face because the nerve that controls the muscles of the face becomes injured or fails to work properly.

Bell's palsy is the most common cause of facial paralysis.

Symptoms of Bell’s palsy tend to appear suddenly over a 48 – 72 hour period, usually affect just one side of the face, and may include:

• Sudden weakness of one side of the face
• Drooping of the mouth or lower part of the face
• Drooling
• Inability to close eye (this results in eye dryness)
• Excessive tearing in one eye
• Facial pain or abnormal sensation
• Altered taste/loss of sense of taste on the front of the tongue
• Intolerance to loud noise
• Distorted facial appearance
• Eyebrow sagging

These symptoms may result in distress and social withdrawal among patients. 

Bell's palsy is caused by an inflammation of the facial nerve. When the nerve swells, it becomes compressed, which hinders its ability to communicate with the facial muscles, resulting in weakness or paralysis. 

While the exact cause of the nerve inflammation is unknown, it is believed it may be caused by a virus. Suspected viral causes include: 

• Herpes simplex virus (HSV)
• Herpes zoster virus
• Cytomegalovirus
• Epstein-Barr virus
• Adenovirus
• Rubella (German measles) 
• Mumps 
• Influenza B
• Coxsackievirus 

Scientists believe that a virus is dormant, and triggers can reactivate it, causing Bell’s palsy. Triggers may include: 

• Impaired immunity 
• Stress
• Sleep deprivation
• Physical trauma
• Minor illness 
• Autoimmune conditions
• Pregnancy
• Preeclampsia
• Obesity
• High blood pressure (hypertension)
• Diabetes
• Upper respiratory illness

A diagnosis of Bell’s palsy is made based on a clinical examination of the patient, and a history of the symptoms with the onset in less than 72 hours. 

Other conditions that can cause facial paralysis must also be ruled out in order to diagnose Bell's palsy, such as stroke, brain tumor, myasthenia gravis, and Lyme disease.  

There are no specific laboratory tests to diagnose Bell’s palsy but some tests may be indicated to help confirm the diagnosis or rule out other conditions:

• Blood tests to rule out other illness
• Electromyography (EMG) 
• Magnetic resonance imaging (MRI) 
• Computed tomography (CT) scan 

Medications used to treat Bell’s palsy include:

• Oral steroids such as prednisone to reduce inflammation within the first 2-3 days of symptoms 
• Antiviral agents (in addition to steroids) such as valacyclovir (Valtrex)
• Antibiotics (if Lyme disease is determined to be the cause)
• Pain relievers 
• Aspirin
• Acetaminophen (Tylenol) 
• Ibuprofen (Advil, Motrin)
• Lubricating eye drops to keep eyes moist when patients are unable to blink
• Artificial tears 
• Eye ointments or gels
• Eye patches 

Therapies that may be used to treat Bell’s palsy include:

• Physical therapy
• Facial massage
• Acupuncture

Surgery to decompress the nerve is controversial and not usually recommended. Rarely, cosmetic or reconstructive surgery is needed to reduce deformities and correct damage such as an eyelid that does not close completely or a crooked smile.

People who have mild cases of Bell’s palsy tend to have more complete recovery. 

Complications of Bell’s palsy include:

• Permanent residual facial weakness 
• Moderate to severe deficits 
• Involuntary mouth movements when trying to blink the eyes 
• Trouble speaking or forming words 
• Scratching of the cornea 
• In a small number of cases, recurrence of Bell’s palsy occurs