Which cranial nerve is associated with bells palsy

Bell's palsy is an idiopathic, acute peripheral-nerve palsy involving the facial nerve, which supplies all the muscles of facial expression. The facial nerve also contains parasympathetic fibers to the lacrimal and salivary glands, as well as limited sensory fibers supplying taste to the anterior two thirds of the tongue (Figure 1). Bell's palsy is named after Sir Charles Bell (1774–1842), who first described the syndrome along with the anatomy and function of the facial nerve. The annual incidence of Bell's palsy is 15 to 30 per 100,000 persons, with equal numbers of men and women affected. There is no predilection for either side of the face. Bell's palsy has been described in patients of all ages, with peak incidence noted in the 40s. It occurs more commonly in patients with diabetes and in pregnant women. Patients who have had one episode of Bell's palsy have an 8 percent risk of recurrence.1,2

Clinical Presentation

Patients with Bell's palsy typically complain of weakness or complete paralysis of all the muscles on one side of the face. The facial creases and nasolabial fold disappear, the forehead unfurrows, and the corner of the mouth droops. The eyelids will not close and the lower lid sags; on attempted closure, the eye rolls upward (Bell's phenomenon). Eye irritation often results from lack of lubrication and constant exposure. Tear production decreases; however, the eye may appear to tear excessively because of loss of lid control, which allows tears to spill freely from the eye. Food and saliva can pool in the affected side of the mouth and may spill out from the corner. Patients often complain of a feeling of numbness from the paralysis, but facial sensation is preserved.

Patients with Bell's palsy usually progress from onset of symptoms to maximal weakness within three days and almost always within one week. A more insidious onset or progression over more than two weeks should prompt reconsideration of the diagnosis. Left untreated, 85 percent of patients will show at least partial recovery within three weeks of onset.3

Etiology and Differential Diagnosis

Bell's palsy is believed to be caused by inflammation of the facial nerve at the geniculate ganglion, which leads to compression and possible ischemia and demyelination. This ganglion lies in the facial canal at the junction of the labyrinthine and tympanic segments, where the nerve curves sharply toward the stylomastoid foramen. Classically, Bell's palsy has been defined as idiopathic, and the cause of the inflammatory process in the facial nerve remains uncertain. Recently, attention has focused on infection with herpes simplex virus type 1 (HSV-1) as a possible cause because research has found elevated HSV-1 titers in affected patients. However, studies have failed to isolate viral DNA in biopsy specimens, leaving the causative role of HSV-1 in question.4,5

Many conditions can produce isolated facial nerve palsy identical to Bell's palsy. Structural lesions in the ear or parotid gland (e.g., cholesteatoma, salivary tumors) can produce facial nerve compression and paralysis. Other causes of peripheral nerve palsies include Guillain-Barré syndrome, Lyme disease, otitis media, Ramsay Hunt syndrome (an outbreak of herpes zoster in the facial nerve distribution), sarcoidosis, and some influenza vaccines. Although these conditions can present as isolated facial nerve palsies, they usually have additional features that distinguish them from Bell's palsy.

Patients with Lyme disease often have a history of tick exposure, rash, or arthralgias. Facial nerve palsies from acute and chronic otitis media have a more gradual onset, with accompanying ear pain and fever. Patients with Ramsay Hunt syndrome have a pronounced prodrome of pain and often develop a vesicular eruption in the ear canal and pharynx, although cases without the vesicular eruption (i.e., zoster sine herpete) have been reported. Polyneuropathies (e.g., Guillain-Barré syndrome, sarcoidosis) will more often affect both facial nerves. Tumors will present with a more insidious onset of symptoms over weeks or months.

Central nervous system lesions (e.g., multiple sclerosis, stroke, tumor) can also cause facial nerve palsy. However, some motor neurons to the forehead cross sides at the level of the brainstem, so the fibers in the facial nerve going to the forehead come from both cerebral hemispheres (Figure 2). Supranuclear (central) lesions affecting the facial nerve will not paralyze the forehead on the affected side, resulting in a unilateral facial paralysis with forehead sparing. Often, there will be at least some weakness of extremities on the affected side as well. Table 11,6–8 summarizes the differential diagnosis of Bell's palsy.

Influenza vaccines in the past have been associated with peripheral neuropathies. Although influenza vaccines currently available in the United States have not been associated with Bell's palsy,9–11 a recently developed Swiss intranasal vaccine was found to have a very high risk of postvaccine facial nerve palsy and has been withdrawn from use.12 Because influenza vaccines change annually, public health officials should be notified of any cases of Bell's palsy occurring in the six weeks following vaccine administration.

Evaluation

A patient with an acute onset of unilateral facial weakness most likely has Bell's palsy. A careful history of the onset and progress of paralysis is important because gradual onset of more than two weeks' duration is strongly suggestive of a mass lesion. Medical history should include recent rashes, arthralgias, or fevers; history of peripheral nerve palsy; exposure to influenza vaccine or new medications; and exposure to ticks or areas where Lyme disease is endemic. The physical examination should include careful inspection of the ear canal, tympanic membrane, and oropharynx, as well as evaluation of peripheral nerve function in the extremities and palpation of the parotid gland. In order to assess forehead involvement, physical examination should also include evaluation of cranial nerve function, including all facial muscles.

Laboratory testing is not usually indicated. However, because diabetes mellitus is present in more than 10 percent of patients with Bell's palsy, fasting glucose or A1C testing may be performed in patients with additional risk factors (e.g., family history, obesity, older than 30 years).13 Antibiotic therapy may be of benefit; therefore, Lyme antibody titers should be performed if the patient's history suggests possible exposure. Signs and symptoms atypical for Bell's palsy should prompt further evaluation. Patients with insidious onset or forehead sparing should undergo imaging of the head. Those with bilateral palsies or those who do not improve within the first two or three weeks after onset of symptoms should be referred to a neurologist

Treatment

CORTICOSTEROIDS

Oral corticosteroids have traditionally been prescribed to reduce facial nerve inflammation in patients with Bell's palsy. Prednisone is typically prescribed in a 10-day tapering course starting at 60 mg per day. A 2004 Cochrane review and meta-analysis of three randomized controlled trials comparing corticosteroids with placebo found small and statistically nonsignificant reductions in the percentage of patients with incomplete recovery after six months (relative risk [RR] = 0.86; 95% confidence interval [CI], 0.47 to 1.59) and the percentage of patients with cosmetic complications (RR = 0.86; 95% CI, 0.38 to 1.98).14 However, these trials included only 117 patients; larger prospective trials are needed to establish the benefit of corticosteroids.

ANTIVIRALS

Because of the possible role of HSV-1 in the etiology of Bell's palsy, the antiviral drugs acy-clovir (Zovirax) and valacyclovir (Valtrex) have been studied to determine if they have any benefit in treatment. Either acyclovir 400 mg can be given five times per day for seven days or valacyclovir 1 g can be given three times per day for seven days. Although a 2004 Cochrane review found insufficient evidence to support the use of these antivirals alone,15 two recent placebo-controlled trials demonstrated full recovery in a higher percentage of patients treated with an antiviral drug in combination with prednisolone than with prednisolone alone (100 percent versus 91 percent and 95 percent versus 90 percent).16,17 However, no benefit was seen when treatment was delayed more than four days after the onset of symptoms (86 percent versus 87 percent).17

SPONTANEOUS RECOVERY

It is difficult to establish a statistically significant benefit of treatment in placebo-controlled trials because Bell's palsy has a high rate of spontaneous recovery. The Copenhagen Facial Nerve Study evaluated 2,570 persons with untreated facial nerve palsy, including 1,701 with idiopathic (Bell's) palsy and 869 with palsy from other causes; 70 percent had complete paralysis. Function returned within three weeks in 85 percent of patients, with 71 percent of these patients recovering full function. Of the 29 percent of patients with sequelae, 12 percent rated it slight, 13 percent rated it mild, and 4 percent rated it severe.3 Because of these findings, some persons have questioned whether treatment for Bell's palsy should be routinely indicated; however, patients who have incomplete recovery will have obvious cosmetic sequelae and will often be dissatisfied with their outcome.18

Given the safety profile of acyclovir, valacyclovir, and short-course oral corticosteroids, patients who present within three days of the onset of symptoms and who do not have specific contraindications to these medications should be offered combination therapy. Patients who present with complete facial nerve paralysis have a lower rate of spontaneous recovery and may be more likely to benefit from treatment.1–3,19

OTHER TREATMENTS

In the past, surgical decompression within three weeks of onset has been recommended for patients who have persistent loss of function (greater than 90 percent loss on electroneurography) at two weeks. However, the most widely cited study supporting this approach only reported results for a total of 34 treated patients at three different sites, included a nonrandomized control group, and lacked a blinded evaluation of outcome.20

The most common complication of surgery is postoperative hearing loss, which affects 3 to 15 percent of patients. Based on the significant potential for harms and the paucity of data supporting benefit, the American Academy of Neurology does not currently recommend surgical decompression for Bell's palsy.19

Some published studies have reported benefit with acupuncture versus steroids and placebo, but all had serious flaws in study design and reporting.21 Table 2 summarizes the available treatments.

Complications

Patients with Bell's palsy may be unable to close the eye on the affected side, which can lead to irritation and corneal ulceration. The eye should be lubricated with artificial tears until the facial paralysis resolves. Permanent eyelid weakness may require tarsorrhaphy or implantation of gold weights in the upper lid. Facial asymmetry and muscular contractures may require cosmetic surgical procedures or botulinum toxin (Botox) injections. In these cases, consultation with an ophthalmologist or cosmetic surgeon is needed.22,23

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