What Is Bell's Palsy? What Causes Bell's Palsy?

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Main Category: Neurology / Neuroscience
Article Date: 27 Jul 2009 - 0:00 PST

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Bell's palsy is either weakness or paralysis of the muscles on one side of the face due to malfunction of the facial nerve. It usually starts suddenly - somebody can wake up in the morning and find that one side of the face does not move. Sometimes one eyelid may be affected, meaning that the patient is unable to blink properly from one eye.

Bell's palsy must not be confused with cerebral palsy, a completely different condition.

Most people who suddenly experience symptoms think they are having a stroke. However, if the weakness or paralysis only affects the face it is more likely to be Bell's palsy.

Approximately 40,000 Americans develop Bell's palsy each year. The National Health Service (NHS), UK, reports that about 25 to 35 people out of every 100,000 develop Bell's palsy each year. It is classed as a relatively rare condition. It more commonly affects people over 15 and under 60 years of age, and affects men and women equally.

Bell's palsy is named after Charles Bell, a Scottish anatomist who first described it in 1821, and published his findings in a Royal Society paper entitled "On the Nerves: Giving an Account of some Experiments on Their Structure and Functions, Which Lead to a New Arrangement of the System".

According to Medilexicon's medical dictionary, Bell's palsy is "paresis or paralysis, usually unilateral, of the facial muscles, caused by dysfunction of the seventh cranial nerve; probably due to a viral infection; usually demyelinating in type."

What are the symptoms of Bell's palsy?

The facial nerves control blinking, opening and closing of the eyes, smiling, salivation, lacrimation (production of tears), and frowning. They also supply the stapes muscles with nerves. The stapes is a bone in the ear which is involved in our ability to hear. When the facial muscle malfunctions, the following symptoms may emerge - symptoms of Bell's palsy:

• Sudden paralysis/weakness in one side of the face.


• It may be difficult or impossible to close one of the eyelids.


• Irritation in the eye because it does not blink and becomes too dry. Changes in the amount of tears the eye produces.


• Parts of the face may droop, such as one side of the mouth.


• Drooling from one side of the mouth. The amount of saliva produced changes.


• Difficulty with facial expressions.


• Sense of taste may become altered.


• An affected ear may lead to sensitivity to sound (hyperacusis). Sounds seem louder.


• Pain in front or behind the ear on the affected side.


• Headache.

What causes Bell's palsy?

The facial nerve controls most of the muscles in the face and parts of the ear. The facial nerve goes through a narrow gap of bone from the brain to the face. This nerve becomes inflamed.

We are not completely certain what the cause of Bell's palsy is. However, experts believe it is most likely caused by a virus, usually the herpes virus, which inflames the nerve. The herpes virus is the one that also causes cold sores and genital herpes. Other viruses have also been linked to Bell's palsy, including the chickenpox and shingles viruses, which are both related to the herpes virus. The virus that causes mononucleosis (Epstein-Barr) as well as the cytomegalovirus have also been linked to Bell's palsy. Lyme disease in areas where it is endemic may be a principal cause of Bell's palsy type symptoms caused by bacteria.

If the nerve is inflamed it will press against the cheekbone or may pinch in the tight corridor (narrow gap of bone) - this can result in damage to the protective covering of the nerve.

If the protective covering of the nerve becomes damaged, the signals which are being sent from the brain to the muscles in the face may not be transmitted properly, leading to weakened or paralyzed facial muscles - Bell's palsy.

How is Bell's palsy diagnosed?

The National Health Service (NHS), UK, as well as the AMA (American Medical Association) say that as treatment is most effective if administered early on, patients should see their doctor as soon as they experience symptoms.

Diagnosing by a process of elimination (diagnosis of exclusion)

The GP (general practitioner, primary care physician) will look for evidence of other conditions which may be causing the facial paralysis, such as a tumor, Lyme disease, or stroke. This will involve checking the patients head, neck and ears. He/she will also check the facial muscles carefully and determine whether any other nerves are affected apart from the facial nerve.

If there is a change in facial structure it could be evidence of a tumor. A characteristic rash may be evidence of tick bites in Lyme disease.

If all other causes can be excluded, the doctor will diagnose Bell's palsy. If the doctor is still unsure, the patient may be referred to an ENT (ear, nose and throat) specialist - an otolaryngologist. The specialist will examine the patient and may also order the following tests:

• Electromyography (EMG) - electrodes are placed on the patient's face. A machine measures the electrical activity of the nerves - and the electrical activity of a muscles in response to stimulation. This test can determine the extent of nerve damage, as well as its location.


• MRI, CT scans or X-rays - these are good at determining whether other underlying conditions are causing the symptoms, such as a bacterial infection, skull fracture, or a tumor.

What are the treatments for Bell's palsy?

Up until 2007, when a major clinical trial was carried out, experts could not agree on which of the following treatments worked best: steroids, antivirals, or a combination of the two. After the clinical trial a consensus emerged among experts that administering steroids alone worked best; specifically, a drug called prednisolone.

• Prednisolone - this steroid is effective in reducing inflammation, which helps accelerate the recovery of the affected nerve. Prednisolone prevents the release of substances in the body that cause inflammation, such as prostaglandins and leukotrienes. Patients take it orally (by mouth), usually two tablets per day, for 10 days. Possible side effects, which usually improve after a couple of days, include:
  
  
  • Abdominal pain, bloating.
  • Acne.
  • Difficulty sleeping.
  • Dry skin.
  • Headache, dizziness (spinning sensation).
  • Increased appetite.
  • Increased sweating.
  • Indigestion.
  • Mood changes.
  • Nausea.
  • Oral thrush (a fungal infection of the mouth) - this can be treated with medication.
  • Slow wound healing.
  • Thinning skin.
  • Tiredness.
  
  
  Allergic reaction to prednisolone - any allergic reaction should be reported to the doctor immediately. Examples may include, hives, breathing difficulties, swelling of the face, lips, tongue, or throat.
  
  If the patient feels dizzy or drowsy he/she should refrain from driving or operating heavy machinery. As this symptom may not appear straight away, it is advisable to wait a day before driving or operating machinery.
  
  Doctors usually reduce the dose gradually towards the end of the course of steroid medication; this helps prevent withdrawal symptoms, such as vomiting or tiredness.


• Eye lubrication - if the patient is not blinking properly the eye will be exposed and tears will evaporate. Some patients will experience a reduction in tear production. Both may increase the risk of damage or infection. The doctor will prescribe artificial tears in the form of eye drops and also an ointment. The eye drops are usually taken during the waking hours, while the ointment is applied before going to sleep.
  
  Patients who cannot close their eye properly during sleep will need to use surgical tape to keep it shut. Patients who experience worsening eye symptoms should seek medical help immediately. If you cannot get hold of your doctor go the emergency department of your nearest hospital.

Most patients make a full recovery within nine months. Those who haven't may have more serious nerve damage, and will require further treatment. This may include:

• Mime therapy - this is a type of physical therapy (UK/Australia/Ireland: physiotherapy). The patient is taught a series of exercises which strengthen the facial muscles. This usually results in better coordination and a wider range of movement.


• Plastic surgery - this can improve the appearance and symmetry of the face. Some patients experience enormous benefit if they are able to smile again. It does not cure the nerve problem.


• Botox - according to researchers of Melbourne's Brain Research Institute, Bell's palsy can be helped by the injection of Botox. The scientists found that specific areas of the brain, including damaged areas responsible for facial movements, may reorganize after injections of Botox combined with facial exercises.

What are the complications of Bell's palsy?

It is important to stress that the vast majority of patients with Bell's palsy make a full recovery. However, if damage to the facial nerve is severe some complications are possible, including:

• Misdirected re-growth of nerve fibers - nerve fibers re-grow in an irregular way. This can result in involuntary contractions of some muscles. A patient may involuntarily close one eye when trying to smile. The problem might be the other way round - when the person closes one eye, the side of the mouth lifts involuntarily.


• Ageusia - chronic (long-lasting) loss of taste.


• Gustatolacrimal reflex - also known as crocodile tear syndrome. While the patient is eating his/her eye will shed tears. It is estimated to occur in about 6% of patients during recovery, and eventually goes away. In some rare cases the problem can be longer lasting.


• Corneal ulceration - when eyelids cannot completely shut, the protective and lubricating tear film of the eye may become ineffective. This can result in corneal drying. The risk or corneal drying is even higher if Bell's palsy has also caused a reduction in tear production. Corneal ulceration can result in infection of the cornea, which can lead to severe loss of vision.

Sources: National Health Service (NHS), UK, The Mayo Clinic, Wikipedia, HHS (Department of Health and Human Services USA), NIH (National Institutes of Health, USA).

Written by Christian Nordqvist


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