Bell’s palsy is a form of facial paralysis resulting from a dysfunction of the cranial nerve VII ( the facial nerve ) causing an inability to control facial muscles on the affected side. Often the eye in the affected side cannot be closed. The eye should be protected from drying up, or the cornea may be permanently damaged, resulting in impaired vision. In some cases denture wearers experience some discomfort. The common presentation of this conditions is a rapid onset of partial or complete paralysis that often occurs overnight. In rare cases ( <1%), it can occur on both sides resulting in total facial paralysis.
Bell’s palsy is defined as a one- sided facial nerve paralysis of unknown cause. Several other conditions can also cause facial paralysis, e.g., brain tumour, stroke, myasthenia gravis, and Lyme disease; however, if no specific cause can be identified, the condition is known as Bell’s palsy. It is thought that an inflammatory condition leads to swelling of the facial nerve. The nerve travels through the skull in a narrow bone canal beneath the ear. Nerve swelling and compression in the narrow bone canal are thought to lead to nerve inhibition or damage.
The condition normally gets better by itself with most achieving normal or near- normal function. Corticosteroids have been found to improve outcomes, when used early while anti- viral medications are of questionable benefit. Many show signs of improvement as early as 10 days after the onset, even without treatment.
Bell’s palsy is the most common acute disease involving a single nerve and is the most common of acute facial nerve paralysis ( >80% ). It is more common in persons between ages 20 and 60. It is named after Scottish anatomist and Edinburgh graduate Charles Bell, who first described it. It is more common in adults than children.
Signs and symptoms
Bell’s palsy is characterized by a one- sided facial droop that comes on within 72 hours. The facial nerve controls a number of functions, such as blinking and closing the eyes, smiling, frowning, lacrimation, salivation, flaring nostrils and raising eyebrows. It also carries taste sensations from the anterior two- thirds of the tongue, via the chorda tympani nerve ( a branch of the facial nerve ). Because of this, people with Bell’s palsy may present with loss of taste sensation in the anterior 2/3 of the tongue on the affected side.
Although the facial nerve innervtes the stapedial muscles of the middle air ( via the tympanic branch ), sound sensitivity and dysacusis are hardly even clinically evident.
Although defined as a mononeuritis ( involving only one nerve ), people diagnosed with Bell’s palsy may have ” myriad neurological symptoms” including ” facial tingling, moderate or severe headache/ neck pain, memory problems, balance problems, ipsilateral limb paresthesias, ipsilateral limb weakness, and a sense of clumsiness” that are ” unexplained by facial nerve dysfunction “.
Some viruses are thought to establish a persistent ( or latent ) infection without symptoms, e.g., the varicella- zoster virus and Epstein- Barr viruses, both of the herpes family. Reactivation of an existing ( dormant ) viral infection has been suggested as a cause of adult Bell’s palsy. Studies suggest that this new activation could be preceded by trauma, environmental factors, and metabolic or emotional disorders, thus suggesting that a host of different conditions may trigger reactivation.
Familial inheritance has been found in 4-14% of cases. Bell’s palsy is three times more likely to occur in pregnant women than non- pregnant women. It is also considered to be four times more likely to occur in diabetics than the general population.
Once the facial paralysis sets in, many people may mistake it as a symptom of a stoke; however, there are a few subtle differences. A stroke will usually cause a few additional symptoms, such as numbness or weakness in the arms and legs. And unlike Bell’s palsy, a stroke will usually let patients control the upper part of their faces. A person with a stroke will usually have some wrinkling of their forehead.
One disease that may be difficult to exclude in the differential diagnosis is involvement of the facial nerve in infections with the Herpes Zoster virus. The major differences in this condition are the presence of small blisters, or vesicles, on the external ear and hearing disturbances, but these findings may occasionally be lacking ( Zoster sine herpete ). Reactivation of existing herpes zoster infection leading to facial paralysis in a Bell’s palsy type pattern is known as Ramsay Hunt Syndrome type 2.
Lyme disease may produce facial palsy. Sometimes the facial palsy occurs at the same time as the classic erythema migrans rash. Other times, it occurs later. In areas where Lyme disease is common, it may be the cause of facial palsy in half of cases.
Bell’s palsy occurs due to a malfunction of the facial nerve ( VII cranial nerve ), which controls the muscles of the face. Facial palsy is typified by inability to control movement in the facial muscles. The paralysis is of the infra nuclear / lower motor neuron type.
It is thought that as a result of inflammation of the facial nerve, pressure is produced on the nerve where it exits the skull within it’s bony canal blocking the transmission of neural signals or damaging the nerve. Patients with facial palsy for which an underlying cause can be found are not considered to have Bell’s palsy per se. Possible causes include tumour, meningitis, stroke, diabetes mellitus, head trauma and inflammatory diseases of the cranial nerves ( sarcoidosis, brucellosis, etc. ). In these conditions, the neurologic findings are rarely restricted to the facial nerve. Babies can be born with facial palsy. In a few cases, bilateral facial palsy has been associated with acute HIV infection. In some research the herpes simplex virus type I ( HSV- 1 ) has been identified in a majority cases diagnosed as Bell’s palsy. This has given hope for anti- inflammatory and antiviral drug therapy ( prednisolone and acyclovir ).
In addition, the herpes simplex virus type-1 ( HSV- 1 ) infection is associated with demyelination of nerves. This nerve damage mechanism is different from the above- mentioned- that Oedema , swelling and compression of the nerve in the narrow bone canal is responsible for nerve damage. Demyelination may not even be directly caused by the virus, but by an unknown immune system response.
Bell’s palsy is a diagnosis of exclusion, meaning it is diagnosed by elimination of other reasonable possibilities. By definition, no specific cause can be determined. There are no routine lab or imaging tests required to make the diagnosis.
Steroids have been shown to be effective at improving recovery in Bell’s palsy while antivirals have not. In those who are unable to close their eyes, eye protective measures are required.
Corticosteroid such as prednisone significantly improves recovery at 6 months and are thus recommended. Early treatment ( within 3 days after the onset ) is necessary for benefit with a 14% greater probability of recovery.
One review found that antivirals ( such as acyclovir ) are ineffective in improving recovery from Bell’s palsy beyond steroids alone in mild to moderate disease.
They are commonly prescribed due to a theoretical link between Bell’s palsy and the herpes simplex and varicella zoster virus. There is still the possibility that they might result in a benefit less than 7% as this has not been ruled out.
Physiotherapy can be beneficial to some individuals with Bell’s palsy as it helps to maintain muscle tone of the affected facial muscles and stimulate the facial nerve. It is important that muscle re- education exercises and soft tissue techniques be implemented prior to recovery in order to help prevent contractures of the paralysed facial muscles. To reduce pain, heat can be applied to the affected side of the face.
Surgery may be able to improve outcomes in the facial nerve palsy that has not recovered. A number of different techniques exist. Smile surgery or smile reconstruction is a surgical procedure that may restore the smile for people with facial nerve paralysis. It is unknown if early surgery is beneficial or harmful. Adverse effects include hairing loss which occurs in 3-15% of people.
Most people with Bell’s palsy start to regain normal function within 3 weeks – even those who do not receive treatment. In a 1982 study, when no treatment was available, of 1,011 patients, 85% showed first signs of recovery within 3 weeks after onset. For the other 15%, recovery occurred 3-6 months later. After a follow- up of at least 1 year or until restoration, complete recovery had occurred in more than two- thirds ( 71% ) of all patients. Recovery was judged moderate in 12% and poor in only 4% of patients. Another study found that incomplete palsies disappear entirely, nearly always in the course of one month. The patients who regain movement within the first two weeks nearly always remit entirely. When remission does not occur until the third week or later, a significantly greater part of the patients develop sequelae. A third study found a better prognosis for young patients, aged below 10 years old, while the patients over 61 years old presented a worse prognosis.
Major complications of the condition are chronic loss of taste ( ageusia ), chronic facial spasm, facial pain and corneal infections. To prevent the later, the eyes may be protected by covers, or taped shut during sleep and for rest periods, and tear- like eye drops or eye ointments may be recommended, especially for cases with complete paralysis. Where the eye does not close completely, the blink reflex is also affected, and care must be taken to protect the eye from injury.
Another complication can occur in case of incomplete or erroneous regeneration of the damaged facial nerve. The nerve can be thought of as a bundle of smaller individual nerve connections that branch out to their proper destinations. During regrowth, nerves are generally able to track the original path to the right destination- but some nerves may sidetrack leading to a condition known as synkinesis. For instance, regrowth of nerves controlling muscles attached to the eye may sidetrack and also regrow connections reaching the muscles of the mouth. In this way, movement of one also affects the other. For example, when the person closes the eye, the corner of the mouth lifts involuntarily.
Around 9% of patients have some sort of sequelae after Bell’s palsy, typically the synkinesis already discussed, or spasm, contracture, tinnitus and / or hearing loss during facial movement or crocodile tear syndrome. This is also called gustatolacrimal reflex and involves the sufferer shedding tears while eating. This is thought to be due to faulty regeneration of the facial nerve, a branch of which controls the lacrimal and salivary glands. Gustatorial sweating can also occur.
The number of new cases of Bell’s palsy is about 20 per 100,000 population per year. The rate increases with age. It affects approximately 1 person in 65 during a life time.
Sir Charles Bell, for whom the condition is named, presented three cases at the Royal Society of London in 1829. Two cases were idiopathic and the third was due to a tumour of the parotid gland.
Dr. A. K. M. Aminul Hoque
Formerly Prof.of Medicine
Dhaka Medical College.