Bell's Palsy

Bell's palsy is facial paralysis due to dysfunction of the 7th cranial nerve, also called the facial nerve, resulting in inability to control facial muscles on the affected side.

Facial paralysis may result from several conditions, e.g., brain tumor, meningitis, stroke, diabetes mellitus, head trauma, myasthenia gravis, Lyme disease, HIV, inflammatory diseases of the cranial nerves (sarcoidosis, brucellosis, etc.) and many others; but when no specific cause can be identified for the paralysis, it is called Bell's palsy. In a few cases, bilateral facial palsy has been associated with acute HIV infection.

By definition, Bell's palsy is idiopathic unilateral facial nerve paralysis, characterized by the rapid onset of partial or complete paralysis often occurring overnight. Rarely (<1%), it occurs bilaterally resulting in total facial paralysis. The condition is usually self-limiting.

A range of annual incidence rates have been reported in literature: 15, 24, and 25–53 (all rates per 100,000 population per year). Its incidence increases with age. It affects approximately 1 in 65 persons during a lifetime. Familial inheritance has been found in 4–14% of cases. Bell's palsy is three times more likely to affect pregnant than non-pregnant women. It is also four times more likely to occur in diabetics than the general population.

Named after Scottish anatomist Charles Bell, who first described it, Bell's palsy is the most common acute mononeuropathy (disease involving only one nerve) and is the most common cause of acute facial nerve paralysis (>80% cases). In general, the etiology and pathogenesis of Bell palsy remain inadequately understood [source: World Health Organization].

CAUSES / RISK FACTORS

Certain viruses are thought to establish a persistent (or latent) infection without symptoms, e.g., Herpes Simplex-1 (HSV-1), Varicella-zoster and Epstein-Barr viruses, all of the herpes family. Reactivation of an existing (dormant) viral infection has been suggested as a cause behind the acute Bell's palsy.

Studies suggest that new activations could be preceded by trauma, environmental factors, and metabolic or emotional disorders, thus suggesting that stress - emotional stress, environmental stress (e.g., cold), physical stress (e.g., trauma) - in short, a host of different conditions, may trigger reactivation.

PATHOLOGY

It is thought that an inflammatory condition leads to swelling of the facial nerve. The facial 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, damage or death.

CLINICAL FEATURES

Mnemonic for easy Memorization

The clinical features of Bell’s palsy can be easily remembered as: BELL’S Palsy
  • Blink reflex abnormal
  • Earache
  • Lacrimation [deficient, excess]
  • Loss of taste
  • Sudden onset; and
  • Palsy of VII nerve muscles
Often the eye on the affected side cannot be closed. The eye must be protected from drying up, or the cornea may be permanently damaged resulting in impaired vision. In some cases denture wearers experience some discomfort.

DIAGNOSIS / DIFFERENTIALS

Bell's palsy is a diagnosis of exclusion; by elimination of other reasonable possibilities. Therefore, by definition, no specific cause can be ascertained. Bell's palsy is commonly referred to as idiopathic or cryptogenic, meaning that it is due to unknown causes.

TREATMENT

Corticosteroids have been found to improve outcomes, when used early, while anti-viral drugs have not. Most people recover spontaneously and achieve near-normal to normal functions. Many show signs of improvement as early as 10 days after the onset, even without treatment. Bell's palsy affects each individual differently.

Treatment modalities have included:
  1. Steroids. 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.
  2. Antivirals. Antivirals (such as acyclovir) are ineffective in improving recovery from Bell's palsy beyond steroids alone. They were however 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.
  3. Physiotherapy. 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 permanent contractures of the paralyzed facial muscles. To reduce pain, heat can be applied to the affected side of the face.
  4. Surgery. Surgery may be able to improve outcomes in 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 hearing loss which occurs in 3-15% of people. As of 2007 the American Academy of Neurology did not recommend surgical decompression.
  5. Complementary therapy. The efficacy of acupuncture remains unknown because the available studies are of low quality (poor primary study design or inadequate reporting practices).

PROGNOSIS

Most people with Bell's palsy start to regain normal facial function within 3 weeks - even those who do not receive treatment. Several studies have shown good recovery in a majority of patients (up to 71% of 1,011 patients in a 1982 study), with only a few (4-12% of the same patients) recovering poorly or moderately, or having long term complications.

Major complications of the condition are chronic loss of taste (ageusia), chronic facial spasm, facial pain and corneal infections. To prevent the latter, 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 cases 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 or Bogorad’s Syndrome 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 [Source: Wikipedia].

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