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What is Bell's palsy?
Bell's palsy is a sudden weakness, drooping or paralysis of some of the facial muscles. It usually occurs on one side of the face. Although the symptoms can be distressing, most people fully recover from Bell's palsy within a couple of months without any treatment.
Signs and symptoms
The symptoms of Bell's palsy tend to develop suddenly - within hours - often worsening over the first 3-5 days. Not everyone gets all the symptoms and they do vary in severity. Bell's palsy usually only affects one side of the face, although on rare occasions it can occur on both sides.
Symptoms of Bell's palsy include:
- Weakness or paralysis of facial muscles, usually on one side of the face;
- Twitching of muscles;
- Face may feel numb, heavy, stiff or pulled to one side;
- Drooping of the eyelid on the affected side of the face;
- Inability to blink or fully close the eye on the affected side of the face;
- One side of the mouth may droop or be lower;
- Difficulty eating, drinking, smiling or talking;
- Food can taste different because of a reduction in the sense of taste in part of the tongue;
- Pain around the ear on the affected side of the face (although this tends to disappear after a few days). Pain is more likely to occur with a herpes zoster infection in the ear, which can also cause Bell's palsy. This is known as Ramsay Hunt syndrome, and;
- Increased sensitivity to sound in the affected ear.
The symptoms of Bell's palsy can be similar to a number of other conditions, some of which, such as stroke, are very serious. Seeking medical attention as soon as possible, once symptoms are noticed, is important to rule out serious conditions and to make sure that treatment is as effective as possible.
Bell's palsy occurs because of inflammation and compression of the facial nerve (also known as the seventh cranial nerve).
The facial nerve carries neural signals between the brain and:
- The facial muscles;
- Some parts of the ear (the skin and some of the tiny muscles inside the ear);
- The salivary gland that produces saliva to help keep the mouth moist;
- The lacrimal gland that produces tears to help keep the surface of the eye moist, and;
- Tastebuds on the tongue.
The facial nerve exits the skull just under the ear, through a bony canal and then branches out across the face. If the nerve becomes inflamed, it can become swollen and compressed inside the canal. This means that blood and oxygen cannot reach the nerve fibres within the nerve, which can lead to damage. It also means that the neural signals cannot pass along the nerve fibres, which lead to the symptoms described above.
Symptoms will depend on the extent of damage to the facial nerve. In some cases, damage may only occur to the layer around the nerve (called the myelin sheath), which acts like an insulator for nerve fibres. In this situation, symptoms will tend to be mild and the recovery rapid. In other cases, more extensive damage may be to the actual nerve fibres, resulting in more severe symptoms and longer period of recovery.
Exactly what causes this inflammation is not completely understood. It is thought that in many cases, it may be due to a viral infection.
Viruses that have been linked with Bell's palsy include:
- Herpes simplex type 1 (which causes cold sores);
- Herpes simplex type 2 (which causes genital herpes), and;
- Varicella zoster (which causes chickenpox).
Other viruses may also cause Bell's palsy and it can also occur as a complication of pneumonia.
Bell's palsy can happen to anyone at any age, although it is less common in children under 15 years of age and in people over 60 years of age. Bell's palsy occurs in men and women equally.
Bell's palsy occurs more commonly in:
- Women who are pregnant;
- People with diabetes, and;
- People who are HIV positive.
Methods for diagnosis
Because the symptoms of Bell's palsy are similar to a number of other conditions that can cause sudden weakness in the facial muscles, part of diagnosing Bell's is to rule out these conditions.
Conditions that can cause similar symptoms include:
- Damage to the facial nerve due to injury to the face or skull;
- Lyme disease, an arthritic infectious disease transmitted to humans by tick bites;
- Middle ear infection;
- Guillain-Barre syndrome;
- Myasthenia gravis;
- Sarcoidosis, and;
- Some tumours (particularly in the parotid glands and the brain).
There is no single test for Bell's palsy. In most cases, a doctor's examination can rule out other causes and diagnose Bell's palsy. If the cause of the facial weakness is not clear, further tests may be required.
Electromyography tests the function of the branches of the facial nerve by measuring the electrical activity in muscles. It can indicate the extent and severity of the nerve damage.
Blood tests can help to identify other problems that may be causing or contributing to muscle weakness, such as diabetes or infections such as Lyme disease.
Magnetic resonance imaging
Magnetic resonance imaging (MRI) uses a magnetic field and radio waves to create an image composed of multiple cross-sections. This creates a detailed image that can be used to identify stroke, tumour or tissue damage.
A computerised tomography (CT) scan uses X-rays to develop a 3D image of the body. It can help to identify problems such as facial fractures, tumours, stroke and infections.
Types of treatment
Most cases of Bell's palsy get better without treatment. However, treatments can help:
- Improve the chance of full recovery or reduce the time it takes for recovery to occur;
- Reduce discomfort or complications while symptoms last, and;
- Help people with long-term Bell's palsy for whom symptoms are permanent.
Treatments that may improve / speed up recovery
Corticosteroids (such as prednisolone) have been shown to help improve the chance of full recovery from Bell's palsy, but treatment needs to start within 72 hours to be effective. Corticosteroids work by helping to reduce inflammation and swelling. For Bell's palsy most people take a short course (around 10 days) of treatment.
Antiviral medications have been used to help to improve recovery from Bell's palsy, but evidence suggests that they are of limited benefit.
Treatments that may help to reduce discomfort and complications
Pain medications such as aspirin, paracetamol, or ibuprofen can help to manage pain associated with Bell's palsy. Moist heat, such as a warm wet cloth applied to the face may also provide relief.
Because the eyelids are affected, it may not be possible for someone with Bell's palsy to blink properly or close their affected eye completely. The front surface of the eye must be kept moist in order to be healthy and for vision to be clear. If it dries out, the eye can become quite painful and vision can be blurred.
Methods to help keep the eye moist include:
- Using 'artificial tear' eye drops, gels and ointments;
- Patching the eye shut, and;
- Taping the eye shut at night.
Facial exercises may help to strengthen muscles and promote recovery of nerve function. They may not be suitable for all people with Bell's palsy.
Relaxation techniques and acupuncture may be helpful during recovery from Bell's palsy for some people.
Treatments for long-term Bell's palsy
Botox® (Botulinum toxin) injections can help people with long-term Bell's palsy in several ways. The effect of these injections is temporary and they will need to be repeated every four months or so.
They may be used to:
- Relax facial muscles of the affected side of the face if they become too tight;
- Reduce unwanted movements of muscles on the affected side of the face because of abnormal nerve fibre regrowth (such as eye-mouth synkinesis);
- Relax facial muscles on the unaffected side of the face if they become overactive and also to improve symmetry and appearance, and;
- Help prevent eye watering when eating.
In some cases of long-term Bell's palsy, surgery may be recommended to help improve the symmetry of the face.
A range of complications can occur with Bell's palsy.
Complications associated with corticosteroid treatment
Corticosteroids, such as prednisolone, can cause side effects. Most of the more serious side effects associated with these medications occur with long-term rather than the short-term use that is required to treat Bell's palsy.
Side effects of prednisolone include:
- Increased sweating;
- Burning in the upper abdomen or chest pain due to irritation of the lining of the stomach or oesophagus;
- Increased hunger;
- Sleeping problems (such as insomnia);
- Dizziness, and;
- Candidiasis (thrush in the mouth).
These side effects generally improve within a couple of days of ceasing treatment.
Some people can also experience mood changes, such as feelings of anxiety, after taking corticosteroids for a short period. If this occurs, or any other side effects that are particularly bothering you, it's important to see your doctor straight away.
Complications associated with long-term Bell's palsy
Most people fully recover from Bell's palsy. However, long-term symptoms can affect around 10% of people. 
Facial muscles can become contracted or permanently tight or tense. This can lead to a greater appearance of facial asymmetry, particularly obvious when one eye appears smaller or a cheek appears larger.
Eye discomfort and damage
If the eyelid muscles are permanently weakened by Bell's palsy, a person is less able to blink and close their eye. This can make the eye dry and uncomfortable and cause blurred vision. The lacrimal gland that produces the tears that coat the front of the eye can also be affected, reducing moisture and causing eye dryness.
The cornea (the clear surface at the front of the eye in front of the iris and pupil) is particularly sensitive to dryness. If it is dry for long periods of time, the cells of the cornea can flake off and this can lead to formation of ulcers. Corneal ulcers can be painful and, if severe, cause significant scarring. This can lead to vision loss.
Unintentional muscle movements (synkinesis)
As the facial nerve recovers from Bell's palsy, new nerve fibres regrow to replace the ones that were damaged. In some cases, nerve fibres can regrow incorrectly. For example, nerve fibres that should connect the brain to the mouth muscles may grow back connecting the brain and the eyelid muscles. This can lead to unintentional movements, as observed with eye-mouth synkinesis. In this condition, when a person is using their mouth muscles to smile or laugh, for example, their eye may wink at the same time.
Crying while eating
Similar to synkinesis, sometimes nerve fibres that usually connect the brain to the salivary gland instead regrow to connect to the lacrimal gland that produces tears. This means that when the salivary gland is stimulated, as with eating, extra tears are produced and the eye waters. This is also sometimes called Borgorad's syndrome or crocodile tears syndrome.
Difficulties with speech
If the muscles that affect mouth movement are affected, slurred speech can occur.
Altered sense of taste
If the branches of the facial nerve that connect the brain to the tongue do not repair properly, the sense of taste can be permanently altered.
Most people with Bell's palsy recover completely. Depending on the severity of the symptoms, recovery can start anywhere from a few weeks to months. In severe cases, onset of recovery may take as long as a year. Around 10% people experience long-term problems with Bell's palsy.
Factors that can make long-term symptoms more likely to occur include:
- Severe initial symptoms including a lot of pain and complete paralysis of the affected side of the face;
- Health conditions such as diabetes and high blood pressure (hypertension);
- Being pregnant when Bell's palsy occurs;
- Being over 60 years of age, and;
- Lack of signs of recovery after six weeks.
Bell's palsy can recur, but this may not happen until years later.
Bell's palsy is less common in children under 15 years of age, but when it does occur, children tend to recover better than adults. Around 95% of children make a full recovery.