Bells Palsy

Bell's palsy is a dysfunction of cranial nerve VII (the facial nerve) that results in inability to control facial muscles on the affected side. Several conditions can cause a facial paralysis, e.g., brain tumor, stroke, and Lyme disease. However, if no specific cause can be identified, the condition is known as Bell's palsy. 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.

Bell's palsy is defined as an idiopathic unilateral facial nerve paralysis, usually self-limiting. The trademark is rapid onset of partial or complete palsy, usually in a single day.

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, damage or death. No readily identifiable cause for Bell's palsy has been found.

Corticosteroids have been found to improve outcomes while anti-viral drugs have not. Early treatment is necessary for steroids to be effective. 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.

Often the eye in 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.

Signs and symptoms

Bell's palsy is characterized by facial drooping on the affected half, due to 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 infranuclear/lower motor neuron type.

The facial nerves control a number of functions, such as blinking and closing the eyes, smiling, frowning, lacrimation, and salivation. They also innervate the stapedial (stapes) muscles of the middle ear and carry taste sensations from the anterior two thirds of the tongue.

Clinicians should determine whether the forehead muscles are spared. Due to an anatomical peculiarity, forehead muscles receive innervation from both sides of the brain. The forehead can therefore still be wrinkled by a patient whose facial palsy is caused by a problem in one of the hemispheres of the brain (central facial palsy). If the problem resides in the facial nerve itself (peripheral palsy) all nerve signals are lost, including to the 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).

Lyme disease may produce the typical palsy, and may be easily diagnosed by looking for Lyme-specific antibodies in the blood. In endemic areas Lyme disease may be the most common cause of facial palsy.

The degree of nerve damage can be assessed using the House-Brackmann score.

Cause

Virus reactivation

Some viruses are thought to establish a persistent (or latent) infection without symptoms, e.g. the Zoster virus of the face and Epstein-Barr viruses, both of the herpes family. Reactivation of an existing (dormant) viral infection has been suggested as cause behind the acute Bell's palsy. Studies suggest that this new activation 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.

Alternative medicine

In traditional Chinese medicine, Bell's palsy is attributed to exposure to wind – more specifically due to wind-cold attacking the Shaoyang (San Jiao, gall bladder) and Yangming (stomach, large intestine) channels as well as the tendons and muscles. This is thought to result in an obstruction of Qi (vital energy) and blood in these areas that leads to malnourishment of the tendons and muscles and thus a propensity for the facial muscles to become lax or paralyzed. Formal studies of the effects of acupuncture on Bell's Palsy are inconclusive (see below, Treatment).

Diagnosis

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. Being a residual diagnostic category, the Bell's Palsy diagnosis likely spans different conditions which our current level of medical knowledge cannot distinguish. This may inject fundamental uncertainty into the discussion below of etiology, treatment options, recovery patterns etc. See also the section below on Other symptoms. Studies show that a large number of patients (45%) are not referred to a specialist, which suggests that Bell’s palsy is considered by physicians to be a straightforward diagnosis that is easy to manage. A significant number of cases are misdiagnosed (ibid.). This is unsurprising from a diagnosis of exclusion, which depends on a thorough investigation.

Treatment

In patients presenting with incomplete facial palsy, where the prognosis for recovery is very good, treatment may be unnecessary. Patients presenting with complete paralysis, marked by an inability to close the eyes and mouth on the involved side, are usually treated. Early treatment (within 3 days after the onset) is necessary for therapy to be effective. Steroids have been shown to be effective at improving recovery while antivirals have not.

Steroids

Prednisone, a corticosteroid, if used early in treatment of Bell's palsy, significantly improves the chances of complete recovery at 3 and 9 months when compared to treatment with the anti-viral drug aciclovir or no treatment at all.

Antivirals

Antivirals (such as acyclovir) have been shown not to be effective 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.

Complementary therapy

The efficacy of acupuncture remains unknown because the available studies are of low quality (poor primary study design or inadequate reporting practices). Surgical procedures to decompress the facial nerve have been attempted, but have not been proven beneficial.
Although defined as a mononeuritis (involving only one nerve), patients 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". This is yet an enigmatic facet of this condition.