What are the causes of Bell's palsy?
It is believed to be due to a swelling of the nerve that controls the muscles of the face.
It can be worrying, but most people make a full recovery.
What is Bell's palsy?
A patient with Bell's palsy on the right side of his face, with the muscles on this side appearing to be paralyzed.
Image credit: Dr. James Heilman
Bell's palsy involves a weakness or paralysis on one side of the face. Symptoms often appear first thing one morning. A person wakes up and finds that one side of their face does not move.
The person may find that they suddenly cannot control their facial muscles, usually on one side. The affected side of the face tends to droop. The weakness may also affect saliva and tear production, and the sense of taste.
Many people are afraid they are having a stroke, but if the weakness or paralysis only affects the face, it is more likely to be Bell's palsy.
Approximately 1 in 5,000 people develop Bell's palsy each year. It is classed as a relatively rare condition.
In very rare cases, Bell's palsy can affect both sides of the face.
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.
If the facial nerve is inflamed, it will press against the cheekbone or may pinch in the narrow gap. This can result in damage to the protective covering of the nerve.
If the protective covering of the nerve becomes damaged, the signals that travel from the brain to the muscles in the face may not be transmitted properly, leading to weakened or paralyzed facial muscles. This is Bell's palsy.
The exact reason why this happens is unclear.
Other viruses that have been linked to Bell's palsy include:
- chickenpox and shingles virus
- coldsores and genital herpes virus
- Epstein-Barr virus, or EBV, responsible for mononucleosis
- mumps virus
- influenza B
- hand-foot-and-mouth disease (coxsackievirus)
Bell's palsy risk factors
Women who are in the last trimester of their pregnancy or who have just given birth may be at risk from Bell's palsy.
Some risk factors have been established.
The condition more commonly affects:
- people aged 15 to 60 years
- those with diabetes or upper respiratory diseases
- women during pregnancy, especially in the third trimester
- women who gave birth less than 1 week ago
Bell's palsy affects men and women equally.
Most people will recover from Bell's palsy in 1-2 months, especially those who still have some degree of movement in their facial muscles.
Treatment with a hormone called prednisolone can speed up recovery. A study found that prednisolone, if administered within 72 hours of onset, can significantly reduce symptom severity and incidence after 12 months.
This steroid reduces inflammation. This 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 by mouth, usually two tablets a day for 10 days.
Possible side effects include:
- abdominal pain, bloating
- difficulty sleeping
- dry skin
- headache, dizziness (spinning sensation)
- increased appetite
- increased sweating
- mood changes
- oral thrush
- slow wound healing
- thinning skin
These side effects normally get better after a couple of days.
An allergic reaction to prednisolone, such as difficulty breathing, should immediately be reported to a healthcare professional.
Any allergic reaction to prednisolone should be reported to the doctor immediately.
Allergy symptoms may include:
- breathing difficulties
- swelling of the face
If the patient feels dizzy or drowsy they 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.
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 in the eye.
The doctor may 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.
In some cases, an antiviral, such as acyclovir may be taken alongside prednisolone; however, evidence that they can help is weak.
Care at home
Facial exercises: As the facial nerve begins to recover, tightening and relaxing facial muscles can help strengthen them.
Dental care: If there is little or no feeling in the mouth it is easy for food to build up leading to decay or gum disease. Brushing and flossing can help prevent this.
Problems with eating: If there are difficulties with swallowing, the individual should chew food well and eat slowly. Choosing soft foods, such as yogurt can also help.
The facial nerves control blinking, opening and closing of the eyes, smiling, salivation, lacrimation (production of tears), and frowning. They also connect with the muscles of the stapes, a bone in the ear involved in hearing.
When the facial nerve malfunctions, as in Bell's palsy, the following symptoms can occur:
- sudden paralysis/weakness in one side of the face
- difficulty closing 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
- dropping in parts of the face, such as one side of the mouth
- drooling from one side of the mouth
- difficulty with facial expressions
- sense of taste may become altered
- an affected ear may cause sensitivity to sound
- pain in front or behind the ear on the affected side
The Bell's Palsy Association in the United Kingdom recommends the following exercises:
- Sit relaxed in front of a mirror
- Gently raise the eyebrows, using the fingers to help, if needed
- Pull the eyebrows together and frown
- Wrinkle the nose
- Breathe in deeply and flare the nostrils
- Try to move the corners of the mouth outward
- Pull one side of the mouth up, then the other, to form a smile
- If you used your fingers, see if you can keep the smile after removing them
To close the eye
- Keeping the head still, look down with your eyes only
- Place one index finger gently over one eyelid to hold it closed
- With the other hand, pull the eyebrow up slightly, massaging along the browline to prevent stiffness
- Without using the hands, gently try pressing the eyelids together
- Hold the eyes half open
The American Medical Association (AMA) say that treatment is most effective when administered early, so patients should see their doctor as soon as they experience symptoms.
They will check the patient's head, neck, and ears. They will also assess the facial muscles to determine whether any other nerves apart from the facial nerve are affected.
If all other causes can be excluded, the doctor will diagnose Bell's palsy.
If the diagnosis is still unsure, the patient may be referred to an ear, nose, and throat (ENT) specialist, or 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 muscle 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.
Most patients make a full recovery within 9 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. 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: Botox injections in the affected side of the face can relax tight facial muscles and reduce any unwanted muscle contractions.
Most people 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 loss of taste.
Gustatolacrimal reflex: Also known as crocodile tear syndrome. While the patient is eating, their eye will shed tears. It 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 of 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.