TITLE: FACIAL NERVE PARALYSIS 1996
SOURCE: Dept. of Otolaryngology, UTMB, Grand Rounds
DATE: March 13, 1996
RESIDENT PHYSICIAN: Kelly D. Sweeney, M.D.
FACULTY: Jeffrey T. Vrabec, M.D.
DISCUSSANT: Kedar K. Adour, M.D., Sir Charles Bell Society, San Francisco, CA
SERIES EDITOR: Francis B. Quinn, Jr., M.D.

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"This material was prepared by resident physicians in partial fulfillment of educational requirements established for the Postgraduate Training Program of the UTMB Department of Otolaryngology/Head and Neck Surgery and was not intended for clinical use in its present form. It was prepared for the purpose of stimulating group discussion in a conference setting. No warranties, either express or implied, are made with respect to its accuracy, completeness, or timeliness. The material does not necessarily reflect the current or past opinions of members of the UTMB faculty and should not be used for purposes of diagnosis or treatment without consulting appropriate literature sources and informed professional opinion."

Anatomy

Acute facial nerve paralysis is a common clinical entity with which all practicing otolaryngologist should be familiar. In order to diagnose and treat the many causes of facial nerve paralysis, it is important that the clinician have a good understanding of the anatomy and function of the facial nerve. The facial nerve contains approximately 10,000 fibers. Of these, 7000 myelinated fibers innervate the muscles of facial expression, the stapedius muscle, the postauricular muscles, the posterior belly of the digastric muscle, and the platysma. The remaining 3000 fibers form the nervus intermedius (Nerve of Wrisberg) which contains sensory fibers (taste) from the anterior 2/3 of the tongue, and parasympathetic secretomotor fibers to the parotid, submandibular, sublingual, and lacrimal gland. The facial nerve also contains a few general somatic afferent fibers which join the auricular branch of the vagus to supply sensation to the external auditory meatus, and visceral afferents which innervate the mucous membranes of the nose, palate, and pharynx via the greater palatine nerve.

The motor nucleus of the facial nerve lies deep within the reticular formation of the pons where it receives input from the precentral gyrus of the motor cortex, which innervates the ipsilateral and contralateral forehead. The cerebral cortical tracts also innervate the contralateral portion of the remaining face. This accounts for the sparing of the forehead motion in supranuclear lesions of the facial nerve.

The parasympathetic secretory fibers of the nervous intermedius arise from the superior salivatory nucleus. These preganglionic fibers travel to the submandibular ganglion via the chorda tympani nerve to innervate the submandibular and sublingual glands, and to the sphenopalatine ganglion via the greater superficial petrosal nerve to innervate the lacrimal, nasal, and palatine glands. The secretory fibers of the lesser superficial petrosal nerve traverse the tympanic plexus, synapse in the otic ganglion, and travel via the auriculotemporal nerve to innervate the parotid gland. Taste fibers from the anterior 2/3 of the tongue reach the geniculate ganglion via the chorda tympani nerve and from there travel to the nucleus of the tractus solitarius.

The facial nerve and nervus intermedius exit the brain stem at the pontomedullary junction and travel laterally 12 - 14 mm with the eight cranial nerve to enter the internal acoustic meatus. The meatal segment of the nerve then travels 8 - 10 mm within the internal auditory canal (anterosuperior quadrant) to the meatal foramen where the canal narrows from 1.2 mm in diameter to 0.68 mm in diameter (the narrowest part of the canal). The labyrinthine segment then runs 2 - 4 mm to the geniculate ganglion. Here the greater superficial petrosal nerve exits to carry parasympathetic secretomotor fibers to the lacrimal gland. Just distal to this branch, the lesser superficial petrosal nerve exits to supply parasympathetic secretomotor fibers to the parotid. The tympanic segment begins just distal to the geniculate ganglion where the nerve turns 40 to 80 degrees (first genu) and runs posteroinferiorly 11 mm across the tympanic cavity to the second genu. A branch leaves the segment near the pyramidal eminence to supply the stapedius muscle. The nerve then turns about 90 degrees at the second genu inferiorly where the mastoid segment travels for 12 - 14 mm inferiorly in the anterior mastoid to exit the stylomastoid foramen. The terminal branch of the nervus intermedius, the chorda tympani, leaves the mastoid segment 5 mm proximal to the foramen and travels lateral to the incus, medial to the malleus to exit at the petrotympanic fissure. The extratympanic segment is composed entirely of motor fibers and enters the parotid gland after giving off the posterior auricular branch and a branch to the posterior belly of the digastric muscle. The pes anserus forms 20 mm from the stylomastoid foramen and further divides the nerve into the upper (temporal, and zygomatic) and lower (buccal, mandibular, and cervical) branches.

Physiology of Nerve Injury

When an axon is injured, biochemical and histological changes occur in the cell body proximal and distal to the site of the injury. The severity of the changes depend upon the distance from the injury to the cell body (proximal injuries usually more severe than distal injuries), the type of injury (crush injuries more severe than clean transections), the age of the patient (older individuals sustain more severe injury than younger patients), and the nutritional and metabolic status of the patient.

Sunderland's classification of nerve injury describes five degrees of injury. The first degree (neuropraxia) involves a localized conduction block in the nerve with the nerve fibers responding to electrical stimuli proximal and distal to the lesion, but not across the injured segment. Axonal continuity is preserved, wallerian degeneration does not occur, and recovery is usually complete.

The second degree of nerve injury is called axonotmesis. This refers to disruption of the axon into proximal and distal portions with interrupted axoplasmic flow. Wallerian degeneration occurs within 24 hours in the distal portion of the axon and to a slight degree in the proximal portion. The connective tissue elements remain intact, however, and the axon may regenerate at a rate of 1 mm/day to the original end organ with the potential for complete recovery.

The third degree of nerve injury refers to endoneurotmesis. In this type of nerve injury, the endoneurium and axon are destroyed, but the perineurium remains intact. Wallerian degeneration occurs. Axons may regenerate, but can be blocked by scar tissue. This will result in partial reinnervation. In addition, misdirection of fibers can occur with resultant synkinesis (abnormal mass movement of muscles which do not normally contract together) and incomplete recovery.

Fourth degree nerve injury is called perineurotmesis. In this type, only the epineurium remains intact, while the axon, endoneurium, and perineurium are disrupted. With this type of injury, wallerian degeneration occurs, and there is much greater chance for aberrant regeneration, synkinesis, and incomplete recovery.

Fifth degree injury or neurotmesis refers to complete disruption of neural continuity. Without careful repair, there is little to no chance of regeneration and recovery. In addition, axonal sprouts may escape the confines of the nerve sheath and produce painful neuromas adjacent to the injured nerve. Except in cases of complete transection, nerve injury is usually a combination of degrees of injury.

Clinical Evaluation

The first step in evaluating any patient who presents with facial nerve paralysis involves taking a careful and thorough history. It is important to determine the onset of the paralysis (sudden vs delayed), the duration, and the rate of progression. It is especially important to determine whether the paralysis is complete verses incomplete. Patients should be questioned regarding previous episodes, family history, associated symptoms (hearing loss, otorrhea, otalgia, vertigo, headaches, blurred vision, parasthesias), associated medical illnesses (diabetes, pregnancy, autoimmune disorders, cancer), history of trauma (recent or remote), and previous surgery (otologic, rhytidectomy, parotidectomy).

A complete head and neck examination must be performed, including microscopic examination of the ears, careful palpation of the parotid glands and neck, ophthalmologic examination (r/o papilledema), auscultation of the neck ( r/o carotid bruits), and a thorough neurological examination. It is important to assess the degree of voluntary movement present in order to document the grade of facial paralysis as described in the House classification system:
Grade Degree Description
I Normal Normal facial movements; No synkinesis
II Slight Mild deformity, mild synkinesis, good forehead function, slight asymmetry
III Moderate Obvious facial weakness, forehead motion present, good eye closure, asymmetry, Bell's phenomenon present
IV ModeratelyObvious weakness, increasing synkinesis; no forehead motion
V Severe Very obvious facial paralysis, some tone present, cannot close eye
VI Total Complete facial paralysis, absent tone

It is also important to determine if the paralysis is central versus peripheral. Supranuclear (central) lesions produce contralateral voluntary lower facial paralysis. The frontalis muscle is spared because of the bilateral innervation as described previously. Emotional response (facial motion on laughing or crying) may also be preserved with central lesions. Presence of Bell's phenomenon (upward outward turning of the eyeball as the patient attempts to close the eyelids) indicates a peripheral lesion.

Any patient presenting with facial paralysis should undergo formal audiological testing, including pure tone, air and bone conduction, speech discrimination, reflexes, and tympanometry. If asymmetry is found on the audiogram, an ABR and/or MRI should be obtained. Electronystagmography (ENG) is usually not indicated unless vertigo or other balance disturbance is part of the clinical picture.

Radiologic evaluation may be undertaken in patients with a history of recurrent paralysis, associated neurological symptoms, suspected CPA lesions, concurrent otologic findings (AOM, COM, suspected cholesteatoma), history of trauma, gradually developing facial nerve paralysis, atypical presentation, or if patients show no evidence of recovery after one month from onset. Gadolinium enhanced MRI is superior for soft tissue evaluation and will usually reveal the inflammation and edema associated with Bell's palsy and with Herpes Zoster oticus. It is also considered to be the procedure of choice to rule out a cerebellopontine angle tumor or other brain tumors. High- resolution computed tomography provides excellent bony assessment and is the study of choice to rule out a temporal bone fracture, or to evaluate the middle ear and mastoid.

Topognostic Testing

The principle behind topognostic testing is that lesions distal to the site of a particular branch of the facial nerve will spare the function of that branch. Moving distally from the brainstem, these tests include: the schirmer test for lacrimation (GSPN), the stapedial reflex test (stapedial branch), taste testing (chorda tympani nerve), salivary flow rates and pH (chorda tympani).

The Schirmer test evaluates the function of the greater superficial petrosal nerve by determining the rate of lacrimation. Filter paper is placed in the lower conjunctival fornix bilaterally. After 3 - 5 minutes, the length of the strip that is moist is compared to the normal side. A value of 25% or less on the involved side or total lacrimation less than 25 mm is considered abnormal. An abnormal result can indicate injury to the GSPN or to the facial nerve proximal to the geniculate ganglion and may predict patients at risk for exposure keratitis.

Stapedial reflex testing is routinely done during the audiological evaluation. This test evaluates the stapedius branch of the facial nerve which leaves the main trunk just past the second genu in the mastoid. Of all the topographic tests, this one is the most objective and reproducible. A loud tone is presented to either the ipsilateral or contralateral ear which should evoke a reflex movement of the stapedius muscle. This changes the tension on the TM (which must be intact for a valid test) resulting in a change in the impedance of the ossicular chain. If the tone is presented to the opposite ear (normal hearing) and the reflex is elicited, the seventh nerve is considered to be intact up to that point. In the case of Bell's palsy with an intact stapedial reflex, complete recovery can be expected to begin within six weeks. Absence of the reflex when either ear is stimulated with normal VIII nerve function suggests an abnormality of the facial afferent. In Bell's palsy, however, absence of the stapedial reflex during the first two weeks is common and is usually of no prognostic significance.

Measurement of taste by the anterior 2/3 of the tongue can be done by placing a small amount of salt, sugar, or lemon juice on the tongue. Loss of taste may indicate interruption of the ipsilateral chorda tympani nerve. This test is extremely subjective. A more reliable indicator of interruption of the chorda tympani nerve involves microscopic detection of the absence of taste papillae on the involved side of the tongue. Papillae generally disappear within 10 days post injury. Examination of the middle 1/3 of the tongue is most indicative, because the anterior 1/3 may receive bilateral input.

Salivary flow rates can also be assessed to evaluate functional integrity of the chorda tympani nerve. This test involves cannulation of Wharton's ducts bilaterally with measurement of output after five minutes. A 25% reduction in flow of the involved side as compared to the normal side is considered significant. This test has largely been abandoned secondary to technical difficulty of cannulating the ducts and patient discomfort. Salivary ph may be examined as an indirect measure of flow. As the rate of flow increases, the ph increases. Therefore, a ph of less than 6.1 may predict loss of function of the chorda tympani.

Although these tests are of historical interest, they have not been found to be of much use clinically for determining the site of the lesion in facial paralysis or for predicting the outcome. Marked discrepancies are often seen. For example, patients may exhibit a marked decrease in lacrimation with a normal stapedial reflex and intact taste, or they may have absent lacrimation and an absent stapedial reflex with normal salivation. These discrepancies are easily explained in Bell's palsy, where there can be multiple sites of inflammation and demyelinization from the brainstem to the peripheral branches of the nerve. In addition, in temporal bone fractures, the GSPN and chorda tympani nerves are very vulnerable to injury and may be disrupted with an intact facial nerve. Also, with tumors, transmission of nerve impulses can occur through the tumor mass itself until late in the disease with different areas of the nerve being affected at different times. These tests may be helpful, however, for predicting the likelihood of development of exposure keratitis.

Electrophysiologic Tests

These tests are useful for patients with complete paralysis for determining prognosis for return of facial function and the endpoint of degeneration by serial testing. They are most useful when considering decompression surgery and are of no value in patients with incomplete paralysis.

The nerve excitability test (NET), maximal stimulation test (MST), and electroneuronography (ENoG) are most useful in the degenerative phase. These tests will give normal results during the first 72 hours after injury due to the stimulating and recording electrodes both being distal to the site of the injury. After 3 - 4 days, the nerve degeneration reaches the site of stimulation and useful results will be obtained. These tests can only be used for unilateral paralysis because all three involve comparison to the contralateral side which must be normal for valid results.

The nerve excitability test (NET) is the most commonly used secondary to the low cost, readily available equipment, and ease of performance. This test involves placement of a stimulating electrode over the stylomastoid foramen. The lowest current necessary to produce a twitch on the paralyzed side of the face (threshold) is compared with the contralateral side. A difference of greater than 3.5 milliamps indicates a poor prognosis for return of facial function. The major draw back to the use of this test is its subjectivity, with reliance entirely on a visual end point. In addition, since such a small amount of current is used with this test, a few intact axons may give a visible response leading the clinician to predict a good prognosis, when in reality most of the fibers are degenerating.

The maximum stimulation test (MST) is a modified version of the NET. A maximal stimulus is used to depolarize all facial nerve branches. The paralyzed side is then compared to the contralateral side and the difference is graded as equal, slightly decreased, markedly decreased, or absent. Testing begins on the third day post onset and is repeated periodically until return of facial function or absent response. An equal or slightly decreased response on the involved side is considered favorable for complete recovery. An absent or markedly decreased response denotes advanced degeneration with a poor prognosis. The response to this test becomes abnormal sooner than the response to the NET and is therefore considered superior. However, like the NET, this test is also subjective.

Electroneuronography (ENoG) is considered to be the most accurate prognostic test because it provides an objective, qualitative measurement of neural degeneration. The facial nerve is stimulated with an impulse transcutaneously at the stylomastoid foramen using bipolar electrodes. The muscular response is then recorded using bipolar electrodes placed near the nasolabial groove. The peak to peak amplitude of the evoked compound action potential is considered proportional to the number of intact axons. The two sides are then compared with the response on the paralyzed side of the face expressed as a percentage of the response on the normal side of the face. A reduction in amplitude on the involved side to 10% or less of the normal side indicates a poor prognosis for spontaneous recovery. A maximal reduction of less than 90% within 3 weeks of onset gives an expected spontaneous rate of recovery of 80 - 100%. Disadvantages of ENoG include discomfort, cost, and test-retest variability which is due to positioning of the electrodes and excitation of the muscles of mastication (V).

Electromyography (EMG) is of limited value early in the evaluation of facial paralysis because fibrillation potentials indicating axonal degeneration do not appear until 10 to 14 days post onset. However, EMG becomes important for assessing reinnervation potential of the muscle two weeks after onset. By using needle electrodes placed transcutaneously into the muscles of facial expression, muscle action potentials generated by voluntary activity can be recorded. Electrical silence can indicate normal muscle in a resting state, severe muscle wasting and fibrosis or acute facial paralysis in the early stages. During normal voluntary contraction organized diphasic or triphasic potentials are seen. Fibrillation potentials indicate degeneration of the neural supply to the muscle in question. Polyphasic potentials indicate reinnervation. These are important because they usually appear 6 - 12 weeks before clinical return of function.

Bell's Palsy

Bell's palsy is the most common cause of facial paralysis and accounts for more than half of all cases. Traditionally, this was considered to be a diagnosis of exclusion after ruling out all other possible causes. However, it has recently been considered a positive diagnosis if the following are present: unilateral weakness of all facial muscles of sudden onset, possibly associated with a viral prodrome, no evidence of central nervous system pathology, no evidence of a CPA lesion, no history of otologic disease. Patients may exhibit evidence of concomitant sensory cranial polyneuritis with otalgia or postauricular pain, dysacousis or hyperacusis, dysgeusia, decreased tearing or epiphora, and facial hypesthesias/dysesthesias of V or IX . Although the exact etiology of Bell's palsy is still unclear, most clinicians believe that herpes simplex infection is the most likely agent. This belief is supported by an increased incidence of HSV antibodies in patients with Bell's palsy when compared to age-matched controls.

In 1995, Sugita et al were successful in producing an acute and transient facial paralysis in mice by inoculating herpes simplex virus into their auricles (104) or tongues (30). Facial paralysis developed in the mice between six and nine days after inoculation, lasted for three to seven days, and then resolved spontaneously. Histopathological studies of the facial nerve and nuclei from these mice revealed severe nerve swelling, vacuolar degeneration, and infiltration of inflammatory cells. HSV antigens were detected in the facial nerve, geniculate ganglion, and the facial nerve nucleus. They concluded that HSV could produce an acute and transient facial paralysis through a natural infectious route from the auricle or tongue to the geniculate ganglion.

Murakami et al (1996) also investigated the role of herpes simplex virus in the pathogenesis of facial paralysis in mice by inoculating mouse auricles with HSV. On the third day following inoculation, HSV DNA was noted in the ipsilateral facial nerve. On the tenth day, HSV DNA was noted in both facial nerves and brain stem in the mice with facial paralysis, but absent in these tissues in the mice without facial paralysis. Between days 4 and 20, the neutralization antibody titer was elevated in all of the mice. In addition, facial paralysis developed only on the inoculated side. They concluded that HSV infection in the facial nerve and brain stem must be a prerequisite for the development of facial paralysis and suggested that an immunologic reaction after a viral infection plays a role in the pathogenesis.

The incidence of Bell's palsy is estimated to be 20 to 30 per 100,000, but appears to increase with age. There is an equal male to female ration and a 3.3 times greater incidence in pregnant females. The left and right sides of the face are equally involved, and less than 1% of cases are bilateral. The recurrence rate is about 10% and can be ipsilateral or bilateral. Patients with diabetes have 4 - 5 times more risk of developing the disease. A family history is positive in about 10% of patients with Bell's palsy.

The most likely site of lesion in Bell's palsy is the meatal foramen (junction of the internal auditory canal portion of the nerve and the labyrinthine segment of the nerve), which is considered to be the narrowest portion of the fallopian canal. MRI with gadolinium will usually show enhancement of the labyrinthine portion of the nerve. As the edema within the nerve increases, axonal flow and circulation are inhibited resulting in varying degrees of nerve injury (first, second, and third degree). Patients who are most severely affected develop a high level of third degree injury which can result in the loss of endoneural tubules and misdirected axonal regeneration. Histological studies from patients with Bell's palsy who died of nonrelated causes reveal diffuse demyelination of the facial nerve with lymphocytic infiltrates.

The prognosis for Bell's palsy is generally good with 85 to 90% of patients recovering completely within one month. The remaining 15% progress to complete degeneration and will not usually show signs of recovery for three to six months. The longer the time needed for recovery, the greater the probability of sequelae. The single most important prognostic factor is the degree of paralysis. Patients with incomplete paralysis will recover with no sequelae 95% of the time.

The treatment of Bell's palsy is variable, ranging from observation to surgical decompression. Regardless of treatment given, all patients must be counselled regarding proper eye care to prevent exposure keratitis. Patients should use natural tears liberally during the day and should place lacrilube ointment in the eye at night. Taping of the eye lids during sleep may be helpful as well as the use of a moisture chamber. Patients should avoid fans and dust, and should consider wearing eye protection when outside in the wind.

Oral prednisone in a divided dosage of 1 mg/kg/day may be helpful in preventing or lessening degeneration, decreasing synkinesis, and relieving pain, and may result in earlier recovery. Patients should be reevaluated within five days after starting steroids. If some function is present (paresis), taper the steroids over the next five days. If no improvement is noted, the full dose should be given for an additional ten days, then tapered over five days. Oral acyclovir may help improve recovery in Bell's palsy. The usual dosage is 500 mg po four times a day for ten days. For patients in whom steroids or acyclovir is contraindicated, observation and eye care may be all that is possible.

Surgical decompression for Bell's palsy is somewhat controversial. Most surgeons agree, however, that in patients progressing to total paralysis within two weeks, with an ENoG demonstrating 90% or greater degeneration, decompression of the facial nerve may prevent further degeneration and may improve outcome. The rationale behind surgical decompression is based on the assumption that the site of maximal facial nerve injury in Bell's palsy is within the meatal foramen. With increasing edema and decreasing axoplasmic flow and microcirculation a pathological compression injury of the nerve occurs at this point of maximal constriction. This can range from first degree to third degree. Removal of the compression, if performed before irreversible injury to the endoneural tubules occurs (two weeks), will allow for axonal regeneration to occur. This is usually accomplished via a middle fossa approach. Surgical decompression should not be done in an only hearing ear.

In a retrospective study, Fisch (1981) compared fourteen patients with >90% degeneration within 1 to 14 days after the onset of facial paralysis who underwent decompression using the middle fossa approach to thirteen similar patients who refused surgical decompression. A subtle but statistically significant improvement in long-term facial recovery was noted in the operative group as compared to the patients who refused surgery. Fisch concluded that in order to obtain a satisfactory return of facial function in all cases of Bell's palsy, surgical decompression of the facial nerve should be performed within 24 hours when results of ENoG indicate >90% degeneration has occurred.

Trauma

Trauma is the second most common cause of facial nerve paralysis. Longitudinal fractures of the temporal bone make up 80% of all temporal bone fractures. In this type, the fracture line extends along the longitudinal axis of the temporal bone resulting in an external auditory canal laceration, TM perforation, and possible ossicular disruption or hemotympanum. Facial nerve injury occurs in 10 to 20% of these fractures with the injury most common in the perigeniculate region. Transverse fractures are much less common (20% of all temporal bone fractures). These fractures extend along the transverse axis of the temporal bone across the vestibule, resulting in sensorineural hearing loss, possible loss of vestibular function, and a 50% chance of facial nerve injury which is also usually in the perigeniculate region.

For complete facial nerve paralysis with clinical evidence of a temporal bone fracture, obtain a high resolution CT scan/temporal bone protocol. If an obvious fracture is present, surgical exploration of the facial nerve should be undertaken as soon as possible via either a transmastoid/translabyrinthine (+ SNHL) or transmastoid/middle fossa approach (- SNHL). During exploration the nerve must be fully exposed in order to identify all injured segments, and remove any compression from fracture fragments. The nerve sheath should be incised and any hematomas within the sheath must be carefully evacuated. If complete transection of the nerve is found during exploration, a direct end-to-end anastomosis should be performed if possible. It is important to handle all neural tissue as atraumatically as possible, using microvascular instruments and techniques. The nerve endings should be prepared by sharply cutting at a ninety degree angle and reapproximating under no tension with two to three 9.0 nylon sutures through the epineurium. When a direct end-to-end anastomosis creates tension, or when segments of the nerve are missing or severely damaged, interpositional grafts from the greater auricular, medial antebrachial cutaneous, or sural nerve should be used.

For incomplete facial nerve paralysis or for delayed onset paralysis associated with a temporal bone fracture, facial nerve testing should be obtained on day 4 after onset. If advanced degeneration has occurred, the nerve should be surgically explored and decompressed.

Gun shot wounds of the temporal bone cause facial paralysis in over 50% of cases. The nerve may be transected, or may be secondarily injured by the kinetic injury from the bullet or from bony fragmentation of the temporal bone. The most common sites of injury are the tympanic and mastoid segments of the nerve and the stylomastoid foramen area. For a complete paralysis after a gun shot wound, surgical exploration and repair should be undertaken as soon as the patient is medically stable. Generally, outcome of facial function is much worse with gun shot wounds to the temporal bone than with temporal bone fractures.

The facial nerve can also be injured during middle ear and mastoid surgery. If iatrogenic transection occurs during surgery, the nerve must be repaired. If paralysis occurs postoperatively and the surgeon is confident that the nerve was intact at the conclusion of the case, a high resolution CT scan should be obtained and facial nerve testing should be done on POD #4 - 6. If advanced degeneration is evident, surgical exploration and decompression should be done. If there is any question as to the integrity of the nerve, exploration should be done as soon as possible by a surgeon familiar with the intratemporal anatomy of the facial nerve and reconstructive techniques.

Penetrating facial injuries with immediate facial nerve paralysis should be explored and repaired as soon as possible while electrical stimulation can still be used to help locate the distal branches. When the injury is medial to the lateral canthus of the eye, aggressive exploration is not usually mandatory because the nerve endings are small and a rich anastomotic network exists in this area.

Herpes Zoster Oticus

Herpes zoster oticus (Ramsay-Hunt Syndrome) is the third most common cause of facial nerve paralysis. This is a manifestation of a dormant varicella zoster virus reactivating in extramedullary cranial nerve ganglia during a period of decreased cell mediated immunity. The prodromal symptoms are very similar to those seen in Bell's palsy, but are usually more severe. Symptoms include severe otalgia, facial paralysis, facial numbness, and a vesicular eruption on the concha, external auditory canal, and palate. Patients may also have varying degrees of SNHL, vestibular symptoms, and associated cranial nerve symptoms. Laboratory evaluation will often show the rise and fall of antibody titers specific for the virus. The palsy is usually more severe and the prognosis much poorer compared to Bell's palsy. Only about 50% of these patients regain normal facial function as opposed to 90% with Bell's palsy. The degeneration occurs more slowly, usually over three weeks instead of two. Treatment includes steroids, valacyclovir 1 gm po tid, and proper eye care. Surgical decompression has not been proven beneficial but may be considered for ENoG showing greater than 90% degeneration.

Otitis Media In patients with evidence of acute otitis media, dehiscences in the fallopian canal may serve as portals for direct bacterial invasion and inflammation along the nerve. Facial paralysis may begin within a few days of onset of an acute otitis media and is usually incomplete. Treatment includes a wide myringotomy, drainage, and culture with antibiotic coverage for gram positive cocci and H. flu. The facial palsy associated with acute otitis media generally resolves with aggressive management of the infection. However, if a total paralysis is present, serial ENoG should be obtained. If axonal degeneration reaches > 90%, surgical exploration and decompression should be performed.

Patients with chronic otitis media may also develop facial paralysis which is usually secondary to cholesteatoma or from inflammation/osteitis compressing the facial nerve. In these cases a high resolution CT should be obtained, and surgery should be performed as soon as possible (tympanomastoidectomy, facial nerve exploration and decompression).

Tumors

About 5% of cases of facial nerve paralysis are caused by tumors. Factors which should increase the clinicians suspicion of a possible tumor include: a slowly developing paresis over more than three weeks, facial twitching, additional cranial nerve deficits, recurrent ipsilateral involvement, associated adenopathy, or a palpable neck or parotid mass. In these cases, MRI and CT should be obtained. The most common benign tumor causing facial nerve paralysis is a facial nerve schwanomma. The most common malignant tumors causing facial paralysis are mucoepidermoid carcinoma and adenoid cystic carcinoma of the parotid gland. The management of facial nerve paralysis caused by tumors depends upon the lesions location, size, and malignant potential and may include transposition of the nerve, division and reanastomosis, interposition grafting, and cranial nerve crossover. After nerve grafts, the best possible result that can be expected is a House grade III paresis.

Melkerson-Rosenthal Syndrome

Melkerson-Rosenthal syndrome is a rare disease that consists of a triad of symptoms: recurrent orofacial edema, recurrent facial palsy, and lingua plicata (fissured tongue). The defining feature of this disease is the persistent or recurrent nonpitting facial edema that cannot be explained by infection, malignancy, or connective tissue disorder. It usually involves the lips and buccal area and may involve the gingiva, palate, and tongue. The lips become chapped, fissured, and red-brown in appearance and may develop permanent deformity after numerous recurrences. Facial paralysis and lingua plicata occur in half of the patients. The complete triad is only present in 25% of these patients. This condition usually starts in the second decade of life, and the manifestations usually occur sequentially (rarely simultaneously). The etiology of this syndrome is unknown. Some consider it a variant of sarcoidosis secondary to biopsies of the lips which may reveal noncaseating granulomas. Facial paralysis occurs in 50 to 90% of these patients and tends to be abrupt. A history of bilateral sequential paralysis and relapse after initial recovery is common. The site of the paralysis usually corresponds to the facial swelling. Facial nerve decompression may be indicated if episodes of facial paralysis are frequent and progressive.

Congenital Facial Paralysis

Newborn facial paralysis is estimated to have an incidence of about 0.23% of live births. The most common cause is birth trauma (80%), which is usually evident by other signs of injury. These include a history of a difficult delivery with or without forceps, facial swelling, bruising over the mastoid or extratemporal course of the nerve, and hemotympanum. The mechanism of injury is thought to be from direct pressure during forceps use or from pressure on the infants face by the sacral prominence during delivery.

Congenital causes of newborn facial paralysis are much less common. Mobius' syndrome consists of a broad spectrum of clinical findings which can range from an isolated unilateral facial paralysis to bilateral absence of facial and abducens nerve function. In this syndrome, the facial nerve forms but consists of only a fibrotic tract. The muscles of facial expression may form in some cases, but degeneration to fibrosis generally occurs rapidly. These children will have no response on EMG at birth and have no chance of spontaneous recovery of facial function. Many other cranial nerves may be involved (III, IV, IX, X, XII) and skeletal abnormalities may be present. Treatment for these causes of newborn facial paralysis is generally delayed until late childhood and usually requires static slings and muscle transfers.

A rare cause of isolated newborn facial paralysis is dysgenesis of the intratemporal facial nerve. CT and surgical findings show that the most common site of the lesion is the distal part of the mastoid segment in the fallopian canal. The nerve is usually very thin and fibrotic at this area. EMG findings in these cases usually show a few functional motor units but useful facial function is not usually present.

Newborns who present with a complete facial nerve paralysis should undergo electrical testing within the first three days of life to differentiate between congenital and traumatic causes. After birth trauma, the nerve can be stimulated for up to five days post injury and fibrillation potentials will be seen on EMG at ten to fourteen days. In congenital cases, the nerve will usually not stimulate and no fibrillation potentials will be seen on EMG. The prognosis for trauma related facial nerve paralysis at birth is usually excellent. Surgical decompression should not be considered until the nerve has had a chance to recover or until >90% degeneration has occurred.

Other Causes

Sarcoidosis consists of a chronic noncaseating granulomatous disease usually characterized by hilar or peripheral adenopathy, polyarthralgias, anergy, elevated serum calcium, and hepatic dysfunction. One variant of sarcoidosis, Heerfordt's disease (a.k.a. uveoparotid fever) consists of uveitis, mild fever, nonsuppurative parotitis, and cranial nerve paralysis. The facial nerve is the most commonly involved cranial nerve and the paralysis usually starts abruptly days to months after the parotitis. In these cases, the paralysis is considered to be from direct invasion of the nerve by the granulomatous process. An elevated serum angiotensin-converting enzyme (ACE) generally confirms the diagnosis, and treatment consists of steroids.

Lyme disease is an infection caused by the tick-borne spirochete Borrelia burgdorferi. Several species of Ixodes ticks carry the spirochete, and the primary reservoir is the white-tailed deer and white-footed mouse. The disease generally occurs in several stages. The first stage consists of a flu-like illness with regional lymphadenopathy, general malaise, and erythema migrans (erythematous enlarging annular skin lesions found anywhere on the body). The second stage usually starts several weeks to months later with neurologic abnormalities. These include meningitis and cranial and peripheral nerve neuropathies. The final stage occurs months to years later in the form of recurrent meningitis, subtle mental disorders or neurologic deficits, and chronic arthritis. Ten percent of these patients develop facial paralysis (unilateral or bilateral) and hearing loss. The facial paralysis typically resolves completely, but may rarely result in mild permanent facial weakness. Treatment for Lyme disease consists of IV ceftriaxone (2 g/day) for fourteen days.

Conclusion

Although Bell's palsy remains the most common cause of acute facial nerve paralysis, it is important for clinicians to consider all causes to avoid overlooking potentially life-threatening diseases. A good history and physical is mandatory in the work-up of these patients and will usually help to significantly narrow the possible causes. Although topognostic testing is of historical interest, it has not proven to be of much use clinically. ENoG is the most useful electrophysiologic test and should be performed within 4 - 6 days post-onset in patients with a complete paralysis with surgical decompression considered for > 90% degeneration. Treatment plans should be individualized in each patient, but must include education on eye protection.

Editor's Comment:

With one exception, the article by Murakami stands as the most recent and perhaps most significant contribution to the understanding of "idiopathic" facial nerve paralysis. The exception is the section in Conn's Current Therapy - 1996 on Acute Facial Paralysis, by Kedar Adour. Dr. Adour discusses the etiology and natural history of the disorder with a clarity rarely matched in our literature. He proposes a diagnostic protocol which discusses manifestations which do NOT permit the diagnosis of Bell's palsy and Herpes zoster paralysis ("exclusion criteria.") He proposes a compellingly rational plan of treatment, in which he suggests that "electrotherpy is of no benefit and may be harmful."

The faculty have invited Dr. Adour to present a Discussion of this Grand Rounds topic, and we are honored that he has agreed to do so.

Discussion by Kedar K. Adour, M.D. President, Sir Charles Bell Society:

Recent published articles have changed the thinking regarding diagnosis and treatment of acute facial paralysis:

Bell Palsy and Herpes Simplex Virus: Identification of Viral DNA in Endoneurial Fluid and Muscle

Shingo Murakami, MD; Mutsuhiko Mizobucbi, MD; Yuki Nakashiro, MD; Takashi Doi, MD; Naohito Hato, MD; and Naoaki Yanagihara, MD

Objective: To determine whether herpes simplex virus type 1 (HSV-1) causes Bell palsy.

Design: Prospective study.

Setting: University inpatient service.

Patients: 14 patients with Bell palsy, 9 patients with the Ramsay-Hunt syndrome, and 12 other controls.

Measurements: Viral genomes of HSV-1, varicella-zoster virus, and Epstein-Barr virus were analyzed in clinical samples of facial nerve endoneurial fluid and posterior auricular muscle using polymerase chain reaction (PCR) followed by hybridization with Southern blot analysis.

Results: Herpes simplex virus type 1 genomes were detected in 11 of 14 patients (79%) with Bell palsy but not in patients with the Ramsay-Hunt syndrome or in other controls. The nucleotide sequences of the PCR fragments were identical to those of the HSV-1 genome.

Conclusions: Herpes simplex virus type 1 is the major etiologic agent in Bell palsy.

The editorial comment:

"One might now question whether we should continue using the term "Bell's palsy" to mean "idiopathic facial paralysis" or whether we should now recognize Bell's palsy as "herpetic facial paralysis," confirming the hypothesis advanced initially in 1972 by McCormick. It is also documented that Adour in 1970 suggested to the American Academy of Otolaryngology that herpes simplex was the cause of Bell's palsy."

Just as the pyramids of Egypt have guarded the riddle of the sphinx, the petrous pyramid of the temporal bone has guarded the secrets of the facial nerve. Even today there is question about the anatomic compartments of the facial nerve. The authors of the above text suggest that the facial nerve carries some parasympathetic secretomotor fibers to the parotid gland and a few general somatic afferent fibers to the external ear. These two suggestions are questionable and are omitted in many neuro-anatomical textbooks. Cutting the facial nerve at the brainstem does not lead to any deficit of parotid secretion nor somatosensory loss in the ear canal. Sunderland's classification of nerve injury is not applicable to herpetic facial paralysis (herpes simplex or herpes zoster). Further, Sir Sydney Sunderland has not written a single word about the facial nerve in his classic textbook. The five degrees of injury are of increasing severity according to the effect of the injury not the cause. The statement "The first degree (neuropraxia) involves a localized conduction block in the nerve with the nerve fibers responding to electrical stimuli proximal and distal to the lesion, but not across the injured segment." is incorrect. Segmental demyelination also causes a neuropraxic state. The terms neuropraxia, axonotmesis, and neurotmesis should not be equated with the 5 degrees of nerve injury.

Under clinical evaluation: The House Grading System cannot be used to document the grade of facial paralysis at the onset of a paralysis. The House system is an "end-stage" interpretation. Grade II includes "mild synkinesis", Grade III and IV "increasing synkinesis". Synkinesis occurs when the nerve has been damaged and then abnormally regenerated. It is not present in the acute stages. The Brackmann modification somewhat addresses this problem and is a modification of the original Adour-Swanson Recovery Profile. "Bell's phenomenon (upward outward tuning of the eyeball as the patient attempts to close the eyelids) indicates a peripheral lesion." is not correct. The eyeball motion described is a normal function of eye muscle activity which only became apparent to Sir Charles Bell because the eyelids did not close. A central lesion with incomplete closure of the eyelids will also display a "Bell's phenomenon."

We agree that topognostic testing is of historical interest only and is invalid in herpetic facial paralysis, or in temporal bone fractures. The presenting symptom of dysgeusia is diagnostic for herpetic facial paralysis. No further diagnostic tests need be done. One hundred per cent of patients with herpetic facial paralysis demonstrate papillitis of the fungiform tongue papillae and has led to the truism that " Bell's palsy is a tongue blade diagnosis." Taste tests using electrogustometry are research tools only. With regards to the stapedial reflex, it should be considered as the "otologists' electromyography". (See below) When should you question the diagnosis of herpetic facial paralysis formerly called Bell's palsy and Ramsay Hunt syndrome??

  1. Partial facial paralysis that does not resolve in 3 to 6 WEEKS.
  2. Partial facial paralysis with electrical evidence of nerve degeneration.
    1. MST in one or more branches with moderate (score of 2) to severe (scoreof 1) decrease in muscle motion.
    2. Global MST less than 3.
    3. Electromyography with fibrillation (denervation) potentials.
  3. Partial facial paralysis with ipsilateral hearing loss.
  4. Any facial paralysis with evidence of chronic otitis media, or history of previous ear surgery.
  5. Progressive facial paralysis over period of weeks or months is not Bell's palsy. Note: Damage to the nerve is complete by day 14 in Bell's palsy but not until day 21 in Ramsay Hunt syndrome.
  6. Total facial paralysis with no regeneration in 4 months. Note: Even with total loss of nerve excitability by ENOG or Global MST 99.9% of all Bell's palsy or Ramsay Hunt Syndrome will regenerate with midface contracture with synkinesis. The earliest sign of regeneration is the return of the stapedial reflex. The next earliest sign is evidence of mouth motion with voluntary forced closure of the eyes (synkinesis).
  7. Total facial paralysis with electrical evidence of nerve degeneration that resolves WITHOUT midface contracture with synkinesis. Note: Facial nerve degeneration with regeneration in Bell's Palsy or Ramsay Hunt syndrome is followed by the sequelae of midface contracture with synkinesis.
  8. Recurrent facial paralysis on the same side with electrical evidence of nerve degeneration and recovery WITHOUT contracture with synkinesis in 4 months.
  9. Stapedial Reflex: The Otologists' Electromyography. Total facial paralysis with intact stapedial reflex is a Partial paralysis! An absent stapedial reflex one week post onset with return of the stapedial reflex by 3 weeks post onset indicates a good prognosis. The Global MST score will allow you to predict rate and degree of recovery.
  10. When reviewing Bell's palsy treatment results be suspicious of any article when the number of patients showing electrical evidence of nerve degeneration does not equal the number of patients with sequelae of contracture with synkinesis.

Electrical stimulation continues to be widely used in the treatment of facial paralysis (20, 23) although there is mounting evidence that it may be contraindicated. It has been suggested that electrical stimulation may interfere with neural regeneration post peripheral nerve injury (24,25) and studies proving its efficacy with facial muscles are lacking in the literature. A 1984 report by the National Center for Health Services Research concluded that "Electrotherapy treatment for Bell's palsy. . . has no demonstrable beneficial effect in enhancing the functional or cosmetic outcomes in patients with Bell's palsy." (26)

Additionally, patients who undergo electrical stimulation acutely may demonstrate more synkinesis and mass action than those who do not (27). It is difficult to produce an isolated contraction of the facial muscles using electrical stimulation due to their small size and close proximity to each other. The contraction produced causes mass action which reinforces abnormal motor patterns and can be painful. (20)

20. Cole J, Zimmerman S, Spector G: Nonsurgical neuromuscular rehabilitation of facial muscle paresis, in Rubin LR (ed): The Paralyzed Face. St Louis, Mosby-Year Book Inc., 1991, pp 107-112.

23. Farragher DJ: Electrical stimulation: A method of treatment for facial paralysis, in Rose FC, Jones R, Vrbova G (eds): Neuromuscular Stimulation: Basic Concepts and Clinical Implication. New York, Demos, 1989 vol 3, pp 303-306.

24. Cohan CS, Kater SB: Suppression of neurite elongation and growth cone motility by electrical activity. Science 1986; 22:1638-1640. 25. Brown MC, Holland RL: A central role for denervated tissues in causing nerve sprouting. Nature 1979; 282:724.

26. Waxman B: Electrotherapy for treatment of Facial Nerve Paralysis (Bell's Palsy). Health Technology Assessment Reports, National Center for Health Services Research 1984; 3:27.

Added Reference:

Jansen JKS, Lomo T, Nicolaysen K, et al: Hyperinnervation of skeletal muscle fibers: Dependence on muscle activity. Science 181:559-561, 1973.

Lack of muscle spindles....

Brodal A: Neurological Anatomy: In Relation to Clinical Medicine, ed 3. New York, Oxford University Press, 1981, pp 495-508.

Dubner R, Seddie BJ, Storey AT: The Neural Basis of Oral and Facial Function. New York, Plenum Press, 1978, pp 222-229. 

March 27, 1996
Kedar K. Adour, MD
President, Sir Charles Bell Society
1000 Green Street #1203
San Francisco, CA 94133
(415) 474-4046   Fax: (415) 474-3541
 E-mail: kadour@aol.com

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Boies, Lawrence R., ed. Fundamentals of Otolaryngology. Philadelphia, PA: J.B. Lippincott Co., 1989.

Cummings, Charles, ed. Otolaryngology - Head and Neck Surgery. St. Louis, MO.: Mosby - Year Book, Inc., 1993.

Fisch U. Maximal Nerve Excitability Testing vs Electroneuronography. Arch Otolaryngol 106: 352 - 357, 1980.

Fisch U. Surgery for Bell's Palsy. Arch Otolaryngol 107: 1 - 11, 1981.

Gates, George A. Current Therapy in Otolaryngology - Head and Neck Surgery. St. Louis, MO.: Mosby - Year Book, Inc., 1994.

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Mattox, Douglas E., ed. The Otolaryngology Clinics of North America: Management of Facial Nerve Disorders. Philadelphia, PA: W. B. Saunders, Co., 1991.

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May M., et al. Natural History of Bell's Palsy: The Salivary Flow Test and Other Prognostic Indicators. Laryngoscope 86: 704 - 712, 1976.

Murakami S, et al. Role Of Herpes Simplex Virus Infection in the Pathogenesis of Facial Paralysis in Mice. Ann Otol Rhinol Laryngol 105: 49 - 53, 1996.

Peitersen E. The Natural History of Bell's Palsy. Am J. Otol 4: 107, 1982.

Rubin, Leonard R., The Paralyzed Face. St. Louis, MO.: Mosby - Year Book, Inc., 1991.

Selesnick SH, Patwardhan A. Acute Facial Paralysis: Evaluation and Early Management. Am J Otolaryngol 15 (6): 387 - 408, 1994.

Sugita T, et al. Facial Nerve Paralysis Induced by Herpes Simplex Virus in Mice: An Animal Model of Acute and Transient Facial Paralysis. Ann Otol Rhinol Laryngol 104:574 - 581, 1995.

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