Bell's Palsy -
What Is It?
Bell's Palsy is facial paralysis, normally affecting one side of the face - In most cases (approx 80%) the condition recedes after 3 months though for a proportion of sufferers the symptoms can continue for longer and in extreme cases indefinately. Most patients suspect they have suffered a stroke when first faced by it's effect and a visit to the doctor helps alleviate their fears. Symptoms normally include; a drooping or sagging mouth, facial pain, drooling, loss of taste, inability to close the eye, resulting in tearing and the need to wear an eye patch - the following article was sourced at the The Department of Neurology at Northwestern University's website and written by Timothy C. Hain, MD (Source)
Bell's palsy is an acquired weakness of one side of the face, due to an injury to the facial nerve. The symptoms on the affected side typically include inability to close the eye, to smile, wrinkle the forehead and whistle. Speech may be mildly slurred. Tearing occurs because the eye does not close completely. Taste sensation may be diminished on the front half of the tongue. Sounds may appear louder on the affected side (hyperacusis) -- this may be caused by paralysis of the stapedius muscle but also occurs independantly. Papillitis may be seen of the fungiform papillae of the affected side. Bell's palsy usually develops over hours to days. The peak involvement usually happens within several days. Mild pain behind the ear is common at onset, as is a subjective sensation of "numbness" of the affected side. Usually it is first noticed when a persons observes it in a mirror, or on eating because food tends to collect between the cheek and gums.
How common is Bell's palsy ?
About 25/100,000 persons per year develop Bell's palsy. The incidence increases slightly with age. There are only minor differences in rates between the sexes and among persons of different race. There is a slightly higher incidence in the winter.
Bells palsy has numerous potential causes. It is presently thought that most cases arise from herpes simplex virus infections (the same one that gives you cold sores in your mouth as well as other variants). However, there are a wide variety of other possibilities including diabetes, sarcoid, HIV infection, and various cancers.
Individuals at increased risk for idiopathic lower motor facial palsy (i.e. facial weakness due to injury to the nerve or facial nerve nucleus in the brainstem) include pregnant women, diabetics, those who have had recent episodes of influenza or respiratory infection, and those with family history of the disease.
Other causes of facial palsy include trauma, CNS disorders, neoplasms and infectious disease (e.g. Lyme disease). Facial palsy is rarely caused by middle ear infection, where it is felt that facial nerve dehiscence may expose the nerve and make it more vulnerable. In acute cases, parenteral antibiotics and myringotomy is generally the treatment. Surgical treatment may be undertaken in patients with epidural abcess, cholesteatoma or mastoiditis.
Diagnosis is based on history, findings on physical examination, and the results of laboratory tests. On physical examination, acutely, the face on the affected side is weak and eye closure is incomplete or absent. Sparing of the forehead would suggest a central facial paralysis rather than Bell's palsy. The naso-labial fold is flattened. Whistling is usually impossible. The tympanic membrane is normal unless there is a herpes infection of the ear (see Ramsey-Hunt syndrome). Other cranial nerves may be affected -- There may be inflamed circumvallate papillae (area supplied by 9), a decreased gag reflex (sensory 9), and palatal weakness (10th). Hearing may be affected due to involvement of the stapedius reflex. On recovery the face may show evidence of misrouting of nerve fibers (see section on prognosis).
An MRI scan will be performed if there is any possibility of a stroke or brain tumor. Tumors are particularly likely if the facial paralysis has gradually evolved over weeks or more, if there is a history of previous cancer, or if there are masses that can be seen in the ear or parotid gland area of the face. Imaging is generally done if there is hearing loss, or slow onset of paralysis (over 6 mo), or if surgical treatment is planned.
Depending on the situation, tests for diabetes, Lyme Disease, sarcoidosis, myasthenia gravis, AIDs, Guillain Barre syndrome, are occasionally performed, especially in persons with weakness on both sides of the face. Lumbar puncture may be necessary (spinal tap) for many of these possibilities.
Specific tests are available to quantify the degree of weakness, but these are not generally felt to be helpful to patient care. ENOG (Electroneurography) is a method of electrically stimulating the nerve. It is not useful during the first 72hrs. At 3 weeks, patients with < 92% degeneration have a uniformly good outcome. Emerging tests are magnetic nerve stimulation. It may provide similar information as ENOG, but without as much potential for pain (from the electrical stimulation).
In 75% of patients, no cause for Bell's palsy is established. It is speculated that a viral infection is the cause of Bell's Palsy in this situation. When a herpes eruption is present on the side of facial weakness, then Ramsey-Hunt syndrome is diagnosed. In addition to the rash, hearing loss is much more common in Ramsay Hunt than most other causes of Bells.
Mild injury causes "neuropraxia". The nerve is still there, it just is slowed down. There is decreased impulse conduction, and prognosis is good. Moderate injury -- may cause interuption of axoplasmic flow and axonotmesis. Wallerian degeneration occurs over 2-3 weeks. Full recovery generally occurs within 2 months. Severe injury is called "neurotmesis". Wallerian degeneration occurs over 3-5 days, misdirected axon regeneration occurs and patients experience prolonged recovery and end up with synkinesis.
Fragmentation, swelling and degeneration is often seen in axon cylinders. There may be lymphocytic infiltration of nerve bundles. Viruses may be found -- HSV, Epstein Barr, mumps, CMV and influenza.
75% of patients with Bell's palsy experience complete recovery, most within 2 to 3 weeks. An additional 15% experience satisfactory recovery, but may have persistent facial asymmetry. 5 to 10% of patients have poor recovery at 4 months with persistent neurologic impairment and cosmetic disfigurement. Many persons with Bells will develop synkinesis. This means that when they blink, the corner of the mouth may twitch slightly. It is caused by a misrouting of facial nerve fibers as it grows back to innervate the facial muscles. Some persons may have "crododile tears", which is tearing when they eat. This is caused by a mixup in autonomic fibers carried by the facial nerve. Others may have "sweating" of the ear when they eat, caused by a similar mechanism.
All patients with Bell's palsy need to take precautions against drying of the eye on the side of facial weakness. This will generally include use of artificial tears during the day, and use of "lacrilube" jelly at night. Eye patches are often counterproductive because the eyelid easily gets dislodged from the patch, allowing the eye to brush against the patch causing discomfort and potential damage. A moisture chamber can be used as an alternative to frequent use of eye drops during the day. The moisture chamber keeps the cornea from drying. In persons who have persistent redness or visual obscuration, a ophthalmologist's help must be enlisted. In some instances, the lid must be sewed shut until facial movement improves. Gold weights can also be placed in the lid to keep it closed.
Prednisone treatment is thought to speed recovery and reduce the frequency of a bad result. Prednisone must be given within the first week of facial weakness, in order to be effective. Usually a dose of about 60 mg is given per day in a single morning dose. This dose is usually continued for about a week, and then tapered off to nothing at about 10 days. In persons at risk, blood pressure, blood glucose and electrolytes should be monitored.
Antiviral treatment for herpes simplex may improve prognosis (Adour, 1996). The protocol used involved acyclovir 400 mg 5 times daily for 10 days. However, recent improvements in antivirals suggest that famciclovir 500 mg tid may be a more effective choice.
Surgery is not needed in most cases of idiopathic Bell's palsy, as 90% of patients recover spontaneously. In cases where there has been trauma, facial nerve decompression may be justified. This area is controversial -- the surgical literature is more optomistic about the benefits of surgery than the medical literature.
Physical therapy is not generally thought to be helpful although it probably doesn't hurt. In persons with severe residual impairments at least 1 year after onset, several surgical procedures are available to improve cosmetic appearance.
Patients with Bell's palsy due to non-herpetic viral infection, sarcoid, diabetes or cancer are treated for these conditions if treatment is available, in addition to the general treatments outlined above.
About 7% of patients have
recurrent Bells palsy. The mean recurrence interval is 10 years. Recurrent
Bells tends to cluster in families as well as diabetics.
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