Timothy C. Hain, MD, Chicago IL. • Page last modified: August 2, 2020
Bell's palsy is an acquired weakness of one side of the face, due to an injury to the facial nerve. Bell's palsy affects 1/60 persons at some time of their life (Sullivan et al, 2016) 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.
Bell's 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) or the Varicella Zoster virus (chicken-pox virus). Bell's due to Zoster is specifically called the Ramsay Hunt syndrome. However, there are a wide variety of other possibilities including diabetes, Lyme disease, sarcoid, HIV infection, trauma, and various tumors (Selesnick and Burt, 2003). Often the terminology regarding Bell's palsy is a bit loose and damage to the nucleus of the facial nerve in the brainstem area is sometimes also termed "Bell's palsy".
Bell's 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 post-traumatic Bells palsy, epidural abcess, cholesteatoma or mastoiditis.
Bell's palsy may be a consequence of ear surgery, even in a delayed fashion, especially when the facial canal is dehiscent (open) within the middle ear. (Xu et al, 2015).
Bilateral Bell's palsy occurs in systemic disorders such as Guillain-Barre syndrome, sarcoidosis, HIV infection, and leukemia
May and Fria (1981) discussed the causes in 170 patients aged between birth and 18 years of age. In their population, pain, vesicles, a red pinna, vertigo, and sensorineural hearing loss suggest herpes zoster oticus. Slow progression beyond three weeks, recurrent facial paralysis involving the same side, facial twitching, weakness, or no return of function after six months indicate a neoplasm. Bilateral simultaneous facial paralysis indicates a cause other than Bell's palsy, such as Guillain-Barre syndrome, pseudobulbar palsy, sarcoidosis, and leukemia. Recurrent facial paralysis associated with a fissured tongue, facial edema, and a positive family history should suggest Melkersson-Rosenthal syndrome.
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. The eye may roll upward on attempted eye closure (Bell's phenomenon)
Movie of Bell's phenomenon -- in the first half, looking at the paralyzed side, eye blinks are weak and the eye rolls up. On the second half, looking at the normal side, blinks are brisk and no eye rolling is seen.
The naso-labial fold is flattened. Whistling is usually impossible. Other cranial nerves may be affected -- There may be inflamed circumvallate papillae (area supplied by cranial nerve 9), a decreased gag reflex (cranial nerve 9), and palatal weakness (cranial nerve 10th). On recovery the face may show evidence of misrouting of nerve fibers (see section on prognosis).
Acoustic reflex testing may be helpful in identifying the site of lesion. Lesions located at the most common place (stylomastoid foramen) result in normal acoustic reflexes. Lesions due to tumors or strokes most commonly will abolish acoustic reflexes.
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.
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. 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 Ramsay Hunt syndrome is diagnosed. In addition to the rash, hearing loss is much more common in Ramsay Hunt than most other causes of Bells.
70-75% of patients with idiopathic Bell's palsy experience complete recovery (Pietersen, 2002) , 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. Patients with zoster (Ramsay Hunt) do worse (Pietersen, 2002).
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. Synkinesis does not improve with time.
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. However, we were told by one of our patients with a 7th nerve palsy that a patch called "Allevyn" works well to prevent injury. 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; Sullivan et al, 2016).
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. Treatment within three days of the onset of paralysis may be necessary for maximal effect of combined treatment with steroids and acyclovir (Hato et al, 2003). From a meta-analysis, the effect size of treatment appears to be a lower incomplete recovery rate of 11.5% for treated, vs. 16.8% untreated (Sullivan et al, 2016).
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 far more optomistic about the benefits of surgery than the medical literature. Surgieries include 12-7 grafting, and decompression of the facial canal. This is generally a very bad idea -- to add surgical insult onto injury. If your ear surgeon suggests this, we think it would be prudent to get another opinion from a non-surgeon.
Physical therapy is not generally thought to be helpful although it probably doesn't hurt.
A recent meta-analysis found only 4 small randomized controlled studies(Cardoso et al, 2008). It seems unlikely to the author of this review that physical therapy has a large effect but practice, particularly in front of a mirror, probably does help with recalibration.
It seems extremely unlikely that physical therapy has any effect at all -- positive or negative-- on the appearence of abberent regeneration.
In persons with severe residual impairments at least 1 year after onset, several surgical procedures are available to improve cosmetic appearance. These include facial plastic surgery, insertion of gold weights, and rarely - -nerve transpositions. We have often observed that patients with weights end up having the weights taken out again because they migrate under the eyelid. In the few patients we have seen who have had nerve transpositions, the effect has generally been difficult to appreciate.
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 with Bell's Palsy get it a second time or more. (Pitts et al, 1988) The mean recurrence interval is 10 years. Recurrent Bells tends to cluster in families as well as in diabetics. A rare variant is Melkersson's Syndrome: multiple recurrence of Bell's palsy and episodic facial edema.