Disclaimer: The information contained within the Grand Rounds Archive is intended for use by doctors and other health care professionals. These documents were prepared by resident physicians for presentation and discussion at a conference held at Baylor College of Medicine in Houston, Texas. No guarantees are made with respect to accuracy or timeliness of this material. This material should not be used as a basis for treatment decisions, and is not a substitute for professional consultation and/or peer-reviewed medical literature. Bell's Palsy Bell's palsy is synonymous with idiopathic facial paralysis. It is the most common cause of an acute facial paralysis, and accounts for 75 to 80 percent of all cases. The annual incidence is 20 to 30 per 100,000. It's name is derived from Sir Charles Bell, a surgeon and accomplished artist from Edinburgh, Scotland who lived from 1774 to 1842. In 1821, he published his anatomic diagrams of the course of the facial nerve and its innervation of the facial musculature. Early treatment strategies for Bell's palsy were primarily surgical. In the 1930's Balance and Duel described decompression of the distal one centimeter of the facial nerve at the stylomastoid foramen. Tumarkin felt that decompression of the stylomastoid artery was necessary to adequately treat Bell's palsy. By the 1940's the main treatment modality was facial nerve decompression in the mastoid segments. In the 1960's electrical testing allowed refinement of the indications for surgery. Jongkees proposed decompression of the nerve when a difference of greater than 3.5 mAmps was noted by nerve excitability testing when comparing the unaffected to the affected side. Alford further delineated indications and discussed the importance of associated symptoms, the cause of the paralysis, and the experience of the surgeon in deciding to proceed with decompression. Important surgical advances were also developed in the 1960's. These include the middle cranial fossa approach which was initially described by House in 1961, and the total facial nerve decompression described by Pulec in 1966. The 1970's was a transition period for the theoretical treatment approach to a patient with Bell's palsy. With the refinement of electrical testing and the use of steroids, a trend had begun away from surgery. Adour was one of the first neurotologists to state that surgery might not be beneficial. In 1985 May discussed the failure of transmastoid decompression to improve outcome. However, Fisch and Esslen found good results after combined middle cranial fossa and mastoid decompression of the facial nerve in 11 out of 12 patients with Bell's Palsy. The role of surgery remains controversial and indication will be discussed later. By the 1980's and 1990's the treatment had changed to being primarily medical. Coker additionally demonstrated that the electrical evidence of a degenerating facial nerve on electroneuronography was reliable and correlated with histologic evidence of neuronal degeneration. Several theories exist regarding the cause of Bell's palsy. Most favor a viral inciting event that triggers edema and inflammation in the nerve leading to infarction and nerve damage. Many viruses have been implicated but there is mounting evidence supporting the herpes simplex virus serotype 1 as the etiologic culprit. Mechanical entrapment in the fallopian canal is the cause of the ischemic injury to the facial nerve. In 1981 Fisch described the "physiologic bottleneck" at the meatal foramen. In his comparative study of adult temporal bone specimens, the average diameter of the fallopian canal was found to be 1.02 to 1.53 mm, except at the meatal foramen where it was 0.68 mm. Histologic examinations have demonstrated hemorrhage and edema in the nerve at this site. Additionally, intraoperative stimulation blockage has been documented to occur in this narrow segment with intact stimulation distally. Nerve injury is classified according to the schema of Sunderland. This system describes progressively worsening injury to the nerve starting with a neuropraxic injury and ending in neuronotmesis or nerve transection. Five grades of injury are described. The grade of the injury correlates to the final functional recovery of the facial nerve. Clinically facial nerve injury is classified using the House-Brackmann system. Grade I is normal function. Grade II shows slight weakness but no synkinesis. Grade III shows obvious weakness with some mass movement. Grade IV has inability to elevate the brow, significant synkinesis, and obvious weakness. Grade V has barely perceptible motion, and grade VI has no movement. The differential diagnosis for facial paralysis is broad and must include inflammatory causes such as herpes zoster oticus or sarcoidosis, traumatic injuries such as temporal bone fractures, mastoiditis, cholesteatomas, the Melkersson-Rosenthal syndrome, and primary or metastatic neoplasms of the temporal bone. By far though, idiopathic facial paralysis predominates. It accounts for almost 80 % of all cases of facial palsy. The epidemiology of Bell's palsy is best described in Peitersen's monograph from the Copenhagen facial nerve study. In over 1000 patients he found there to be no sex predilection. A broad age range was noted, typically from 15 to 60 years old. Rarely did he note bell's palsy in patients less than 15 years of age. Patients presented with a classic constellation of symptoms. There is usually a prodrome of periauricular pain that heralds the onset of facial palsy within 24 hours. The palsy is unilateral and involves all muscle groups. In order to make the diagnosis of Bell's palsy the evaluating clinician must exclude the following: concurrent CNS disease, otologic infection, auricular blebs suggesting the Ramsey-Hunt syndrome, parotid masses, and an occult neoplasm such as a facial neuroma in a patients who has a recurrent palsy. There is no consensus regarding the work up of a patient with Bell's palsy. Most would include a routine basic audiogram in order to rule out an asymmetric hearing loss, which might suggest another process. Topognostic tests, which include the Schirmer's test of tearing, the salivary flow test popularized by May, and the acoustic reflex test are of historic interest only. While once felt to assist in localizing the nerve injury, we know now that the injury occurs at the meatal foramen. Additionally, they do not offer prognostically valuable information. Radiographic imaging is reserved for those who have no improvement in there palsy within 6 months and for those who a have recurrent palsy. The MRI is the best study to image the facial nerve. In patients with Bell's palsy gadolinium MRI enhancement of the perigeniculate region is prominent. However, as Schwaber pointed out in 1990, this enhancement does not correlate with outcome. Furthermore, Gribarski showed that 76% of normal subjects will show enhancement of the perigeniculate region with gadolinium. Electrodiagnostic test are reserved for patients with complete facial paralysis. Available tests include the nerve excitability test(NET), maximal stimulation test(MST), electroneuronography (ENog), and electromyography. The latter is appropriate when the paralysis has been present for several weeks. In the acute period the first three are most appropriate. NET and the MST are both performed using the Hilger stimulator. The first is a threshold test and the second a supramaximal stimulation test. A criticism of these two tests is that the grading of the response to the stimulus is subjective, and thus may not reliably predict denervation. However, Coker and Fordice demonstrated that a greater than 3.5 mAmp difference side-to-side on NET correlated closely with objective ENog data showing greater than 90% degeneration of the nerve. May showed that in patients who did not have a response to the MST for 10 days, over 85% did not fully recover. Those who did have a response to MST within the first 10 days had excellent recovery. Enog is the most widely used test to evaluate an acute complete facial paralysis. It is an objective reliable test that compares the difference in the amplitude of the compound action potential of the unaffected to affected side of the face. Fisch and Esslen found that when the amplitude of the affected side is less than 10% of the unaffected side the prognosis is poor. Coker correlated the evidence of electrical degeneration with histologic evidence of nerve degeneration. Treatment of an acute facial paralysis is initially medical. The regimen currently used by most otologists is prednisone 1mg/kg/day tapered over a 10 day period. With the mounting evidence implicating the herpes virus, many additionally recommend acyclovir 800 mg three times a day for 10 days. Indications for surgery are controversial, but most neurotologists feel that electrical evidence of greater than 90% degeneration or a difference of 3.5mAmp from side-to-side is sufficient to proceed with a decompression. Surgery must be performed as early as possible. After 21 days there is probably no benefit. The decompressive surgery must focus on the meatal foramen. May found that transmastoid decompression alone did not improve outcome, whereas when combining transmastoid and middle cranial fossa decompression Fisch found good outcome in 11 of 12 patients . Good prognostic variables include presentation with an incomplete palsy, onset o f return of facial function within three weeks, and age below 60 years. Peitersen found that 94% of patients who presented with an incomplete palsy progressed to full recovery. If return of facial function was within one week almost 90% fully recovered Return of function in the second and third weeks yielded full recovery in 83% and 60% respectively. Overall, 85% of patients with Bell's palsy will recover to normal function. In conclusion, Bell's palsy is the most common cause of an acute facial palsy. It is unilateral and sudden in onset, often with a prodrome of auricular pain. After excluding other potential causes of a facial paralysis, treatment is with prednisone and acyclovir. Surgery is reserved for those who meet electrodiagnostic criteria or are worsening on medical treatment. Decompression must include the site of pathologic compression of the facial nerve, the meatal foramen. Finally, fortunately 85% of patients with Bell's palsy have full return of facial function. Case Presentation A white female initially presented at the age of 29, with a 16-day history of a complete right-sided facial paralysis. Complicating this problem was the fact that she was also 34 weeks pregnant. No complaints of associated dizziness or changes in her hearing were reported, but she did note some facial dysesthesias in the distribution of the mandibular branch of the trigeminal nerve. There was no history of recurrent facial edema or a fissured tongue. Physical exam did not show any auricular blebs or parotid masses. An audiogram was normal with the exception of absent right-sided acoustic reflexes. Nerve excitability testing showed a good response at 3.0 milliamps on the unaffected side and no response at 7.0 milliamps on the right. Because of her pregnancy and late presentation she was not offered further treatment. Her recovery was incomplete. In May, she began to notice some unusual movements and spasms in her face. Final recovery left her with good symmetry at rest and excellent eye closure, but she had mild brow ptosis, synkinesis, and gustatory tearing. She was graded according to the House-Brackmann scale as a III out of VI. She subsequently did well with some intermittent dysesthesias of the right face until age 36 when she suffered an attack of Bell's Palsy on the left side of her face. She was treated with prednisone and acyclovir and eventually fully recovered. Approximately two years later she experienced two recurrences of her right-sided facial paralysis. Both episodes were treated with prednisone and acyclovir with recovery to her baseline grade III deficit. She is currently being followed by the neurotology service at The Methodist Hospital to monitor any further recurrence. Bibliography Abraham-Inpijn L, Oosting J, Hart AAM. 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