What is Bell's palsy?
This form of acute facial paralysis arises from inflammation of the facial nerve that controls the muscles used for facial expressions.
The most common type of facial palsy, it affects around 40,000 people in the US, 8000 in the UK, and one in 5000 worldwide, each year. It afflicts men and women equally and at any age, although it is more common with age. Diabetics, pregnant women and those with colds/flu or an upper respiratory tract infection are more susceptible to Bell's palsy.
Its main feature is one-sided facial weakness or paralysis, with poor or no muscle control. Symptoms include involuntary facial twitches, difficulty in closing the affected eye and a corner-of-the-mouth droop. It can also produce dry eyes or excessive tearing, a dry mouth, taste disturbances and hearing problems.
What causes it?
Although the cause of the neural inflammation is still under debate, a likely culprit is the herpes simplex virus (HSV-1), which accounts for at least 60-70 per cent of cases. Almost everyone is exposed to the virus at some point through infected saliva by, for example, kissing, or sharing towels or cutlery. Most HSV-1 carriers aren't even aware of it, as the virus can lie dormant in the body.
A weakened immune system - due to stress, infections or chronic autoimmune conditions, for example - is the most likely trigger for reactivating HSV-1. When this happens, antibodies are produced, leading to an inflammatory response.
The prognosis for Bell's palsy is generally good. Around 75-80 per cent of cases will resolve without treatment (Am J Otol, 1982; 4: 107-11), with major improvements within three weeks. Patients with partial paralysis tend to have better outcomes, with 94 per cent making a full recovery (BMJ, 2004; 329: 553-7). However, those with complete facial palsy, severe nerve degeneration or who fall into the high-risk group (diabetics, pregnant women, over-60s) have poorer prognoses.
What doctors tell you
There is no standard treatment or cure for Bell's palsy. Many doctors prescribe antiviral drugs or steroids, usually acyclovir or prednisone. However, a review of the available evidence shows no significant benefits from steroids (Cochrane Database Syst Rev. 2002; 1: CD-001942; Laryngoscope, 1984; 94: 1472-6), and mixed results with acyclovir (Cochrane Database Syst Rev, 2001; 2: CD-001869). As steroids come with a well-known list of side-effects, these risks need to be weighed against the fact that most cases of Bell's palsy resolve on their own.
Another treatment, reserved only for those whose nerve damage is severe, is nerve decompression, where bone from the nerve's route along the base of the skull is surgically removed to allow the nerve to heal. It is best done within two weeks of total facial paralysis (Laryngoscope, 1999; 109: 1177-88). However, this is a highly complicated procedure with an unpredictable success rate, and little evidence of substantial patient benefits to justify the risks (Acta Otolaryngol Suppl, 1988; 446: 101-5).