The most common form of facial paralysis is Bell’s palsy. The incidence is reported to be approximately 25 cases per 100,000 populations per year. The lifetime risk of getting Bell’s palsy is 1 in every 60 person.

What are the symptoms of Bell’s palsy?

Bell’s palsy is acute facial palsy (paralysis). Bell’s palsy starts abruptly and generally attains maximum weakness in 2 days (48 hours). Sometimes pain in the face and behind the ear may precede weakness (paralysis) by a day or two till the patient of the family notice that there loss of movement in one side of the face. Sometimes patient describe the face as being numb (but there is no evidence of lack of sensation except taste). There may be loss of taste sensation in one side of the tongue. There may also be hyperacusis (an exceptionally acute sense of hearing and occurs due to involvement of nerve to stapedius). Generally approximately 80% of the patients of Bell’s palsy recover in few weeks or months time and presence of incomplete paralysis in the first week of starting of Bell’s palsy is the most favorable sign for good prognosis.

On examination of the patient of Bell’s palsy there is weakness or paralysis of the facial muscles on one side and failure to close eye. The mouth is drawn to the normal side and there may be drooling of saliva from mouth. The tongue also looks deviated towards normal side which is due to distortion of the mouth and not due to weakness of the tongue muscles. Sometimes there may also be dysarthria (imperfect articulation of speech) of some degree.

What is the pathophysiology of Bell’s palsy?

In most of the cases of Bell’s palsy the correct pathophysiology is not known. Bell's palsy is sometimes associated with the presence of herpes simplex virus (HSV) type 1 in endoneurial fluid and posterior auricular muscle. However, HSV can cause Bell's palsy is unproven. An increased incidence of Bell's palsy is also seen among recipients of inactivated intranasal influenza vaccine. From this observation it was hypothesized that this could be due to the Escherichia coli enterotoxin that is used as adjuvant.

What other diseases can cause similar symptoms of Bell’s palsy?

There are several diseases which can cause facial palsy and all these should be considered before coming to a diagnosis of Bell’s palsy. Lyme disease (caused by Borrelia burgdorferi), the Ramsay Hunt syndrome, sarcoidosis, Guillain-Barré syndrome, leprosy, acoustic neuromas etc. can cause facial palsy as a symptom and these should be ruled out before diagnosing a case of Bell’s palsy. Lyme disease can cause unilateral or bilateral facial palsy and in endemic areas more than 10% of cases of facial palsies are due to lyme disease. Ramsay Hunt syndrome also causes severe facial palsy which is due to reactivation of herpes zoster virus, but there is a vesicular eruption in the external auditory canal and sometimes in the pharynx. In Guillain-Barré syndrome and sarcoidosis, the facial palsy is bilateral. Facial palsy due to leprosy generally has other symptoms of leprosy.

How Bell’s palsy is diagnosed?

Bell’s palsy can be generally diagnosed based on clinical finding. The clinical findings which aid the diagnosis of Bell’s palsy are typical presentation of symptoms, absence of cutaneous lesions of herpes zoster in the external ear canal, no risk factors or any preexisting symptoms of other causes of facial palsy, except facial nerve the neurological examination is generally normal in Bell’s palsy. Attention to the eighth cranial nerve is essential due to its course near to the facial nerve.

In uncertain and atypical cases of Bell’s palsy, an ESR, testing for diabetes mellitus, a Lyme titer (to rule out Lyme disease), angiotensin-converting enzyme and chest imaging studies for possible sarcoidosis, a lumbar puncture for possible Guillain-Barré syndrome, or MRI scanning should be done to rule out the other causes of facial palsy. MRI can sometimes show swelling of the facial nerve in idiopathic Bell's palsy.

How Bell’s palsy is treated?

Approximately 70–80% of the patients of Bell’s palsy recover spontaneously within 2-12 weeks time. Symptomatic treatment of Bell’s palsy includes use of paper tape to depress the upper eyelid during sleep and prevent drying of cornea and massage of the weakened facial muscles. A course of glucocorticoids therapy (but the glucocorticoid therapy has to be initiated within 48 hours of onset of Bell’s palsy) like prednisone 60–80 mg daily during the first 5 days and then tapered over the next 5 days should be given, which can shorten the recovery period (although only a little bit) and improve the functional outcome though only modestly. In a recently concluded randomized trial found that there is no benefit of acyclovir (an anti viral antibiotic) compared to glucocorticoids (like prednisolone) alone for treatment of acute Bell's palsy. The value of other antiviral drugs is not known.

What is the prognosis of Bell’s palsy?

Prognosis is worse if the patient is elderly and with complete facial paralysis. If response is preserved and there is a measurable blink reflex the prognosis is good. If the paralysis is severe there may be axonal degeneration and the recovery is slow and incomplete. Sometimes there may be unwanted facial movements (e.g. when mouth is moved eye may close) due to inappropriate reinnervation, which can add to facial disfigurement. This problem can be solved sometimes by locally injecting Botulinum toxin into the affected muscle.