Herpes zoster oticus

Idiopathic facial (Bell's) palsy is an affliction commonly seen and managed by the family physician. Although the prognosis is generally good, steroids and cromolyn sodium have each been advocated to enhance full recovery. Surgical exploration of the nerve is indicated when the diagnosis is unclear. Various measures maybe necessary to protect the eye. Idiopathic facial (Bell's) palsy has traditionally been considered a benign weakness isolated to the infratemporal portion of the facial nerve. This description of the disease has remained relatively unchanged since the original observations were made almost 200 years ago. Interestingly, the observations of Sir Charles Bell, whose name is associated with the condition because of findings that he published in 1821, were actually preceded by those of Nicholaus A. Friedreich and Richard Powell, whose reports were published in 1798 and 1813, respectively.

More recent research suggests that Bell's palsy is actually a multiple cranial neuropathy (Figure 1). The facial palsy may be partial or complete, equally affecting all of the facial muscles on one side of the face (Figure 2). In addition to the typical facial weakness, patients commonly exhibit other manifestations of facial nerve involvement, including facial or retroauricular pain (60 percent of cases), dysgeusia (57 percent), hyperacusis (30 percent) and decreased tearing (17 percent ) Altered conduction velocities in clinically unaffected nerves of the arm have also been demonstrated in patients with Bell's palsy.5 Thus, seventh-nerve palsy may be merely the most apparent symptom of a more generalized polyneuritis.

Illustrative Case

A 42-year-old woman sought treatment at an emergency department because of inability to blink her right eye or move the right side of her mouth. Her symptoms had begun the evening before with "an airy feeling" in the right eye. Later, while looking in the mirror, the patient realized this symptom was associated with difficulty in blinking. The next morning, she discovered that the weakness had progressed to include the entire right side of her face and that she was able to close her right eye only with extreme effort. She also had pain behind her right ear. At this point, the patient decided to seek medical attention because of the concern that she had suffered a stroke.

The patient reported that she had had a "stomach virus" approximately one week before the onset of the palsy. She had not experienced similar episodes in the past and did not have a history of oral herpes infection. Other aspects of the history, including past medical history, family history and social history, were unremarkable.

On physical examination, the patient appeared well except for an obvious rightsided facial paralysis. Blood pressure was 126/84 mm Hg and temperature was 36.9 deg. C (98.40 F). Physical findings were normal, with the exception of weakness equally affecting all the facial muscles on the right side of her face. All other cranial nerve function remained intact. No other motor weaknesses or sensory deficits were noted, deep tendon reflexes were normal, primitive reflexes were absent, and cerebellar function appeared to be intact. The patient had no skin lesions, no evidence of trauma in the affected area, and no nodes or masses indicative of regional malignancy or metastatic disease. Ear examination was normal.

The diagnosis of idiopathic facial (Bell's) palsy was made, and no further investigation was undertaken. After reassuring the patient, discussing the etiology and prognosis of Bell's palsy, and instructing her in eye care, the emergency department physician discharged the patient without medication, advising her to see her family physician in five days.

In a follow-up telephone conversation 12 days after the onset of the weakness, the patient reported that she was beginning to notice some improvement in her mouth movement, although the other muscles of her face remained weak. With the exception of a decreased sensation of taste on the right side of her tongue, she reported that no other symptoms had developed. Her family physician had prescribed electric physiotherapy, which relieved a sensation of tightness in her face. By six months after the onset of facial paralysis, the patient had made a complete recovery. Incidence

The reported incidence of Bell's palsy varies from eight to 240 per 100,000, with the majority of studies indicating a range of 13 to 34 per 100,000. There is no statistical difference in the age-specific rates between men and women.', Many authors', report that the incidence is highest among the age group from 20 to 35 years, while at least one studys found no significant age-related prevalence. The right and left sides of the face are affected with equal frequency. One study 8showed that 6.3 percent of patients had had previous episodes of facial palsy and that 1.4 percent had a positive family history; similar findings have been reported by other investigators .

Prognosis

The prognosis for Bell's palsy is generally regarded as very good, with complete recovery occurring in approximately 86 percent of patients . Incomplete recovery has been associated with several risk factors, including hypertension, age over 55 years, complete facial weakness, pain other than ear pain, and changes in tearing .

Evoked electromyography has been suggested as the most accurate, objective and reliable prognostic test. Dividing patients' responses to evoked electromyography into greater than 25 percent, ll to 24 percent, and 10 percent or less, May and associates'2 found satisfactory recovery to be 98 percent, 84 percent and 21 percent in each group, respectively.

Adour and Hetzler suggested that testing the stapedial reflex alone can predict the outcome in 80 percent of patients. If the stapedial reflex remains present throughout the course of the disease and facial paralysis is incomplete, full recovery generally occurs within three to six weeks. If the reflex is absent during the first week but retums by the second or third week, facial function usually retums within four to eight weeks, with only minimal residual impairment.

Differential Diagnosis

Accurate assessment of facial paralysis is important for the selection of the most effective medical therapy and estimation of the prognosis. To aid in diagnosis, Adour and Hetzler have proposed a practical classification system for the differentiation of facial paralysis (Table 1).

In the majority of cases, the correct diagnosis can be made from a thorough history and physical examination. Special attention should be given to the onset and duration of symptoms and to signs of subtle involvement of other cranial nerves. The cranial neuritis of herpes zoster with facial nerve paralysis (herpes zoster oticus or Ramsay Hunt syndrome) can have a clinical course and cranial nerve involvement similar to those of Bell's palsy. The two conditions may be differentiated by the greater severity of symptoms, the presence of vesicles and a rising titer to herpes zoster virus in Ramsay Hunt syndrome.

Etiology

The exact etiologic agent in Bell's palsy remains unknown. The histologic characteristics, however, have been described. The Schwann cells undergo chromatolysis and ballooning of the nuclei, with associated edema and disruption of nerve transmission. Subsequent lymphocytic infiltration may then cause fragmentation of the myelin sheath with resultant demyelination. The peripheral axons mayalso be affected, leaving damaged but potentially repairable nerves. Provided that the distal edema and inflammation resolve, remyelination and functional muscle innervation occur. Vascular insufficiency, viral infections (including mumps, rubella, herpes simplex, herpes zoster and Epstein-Barr) and the spirochete Borrelia burgdorferi have all been implicated as possible causes of the ailment.'

An increased incidence of Bell's palsy has also been noted in patients with leukemia and lymphoma not associated with malignant invasion of the facial nerve. These findings, along with the implication of Epstein-Barr virus and HTLV-1 in the pathogenesis of lymphoid malignancies, again raise the possibility of a virus-related etiology.

Adour and associates' 4from the Facial Paralysis Research Center, Oakland, Calif., strongly support the hypothesis that Bell's palsy is caused by the reactivation of latent herpes simplex virus. In a study of the sera of 41 patients with Bell's palsy and 41 matched controls, both acute-phase specimens (those taken within seven days of symptom onset) and convalescent-phase specimens (those taken two weeks later) were examined for complement-fixing antibody to herpes simplex virus, herpes zoster virus, adenovirus, influenza A and B, cytomegalovirus and Mycoplasma pneumoniae. The only difference observed between the patient group and the control group was in herpes simplex antibody titers. Every patient with Bell's palsy had antibodies to herpes simplex virus, as compared with 85 percent of the controls. In addition, none of the Bell's palsy patients demonstrated the fourfold or greater increase in herpes simplex titer that would have occurred between the acute-phase and convalescent-phase specimens if the antibodies were due to primary infections.

Isolation of herpes simplex virus from the trigeminal ganglia of unselected cadavers is cited by Adour 14 as evidence that cranial nerve ganglia can harbor latent virus. In addition, factors commonly associated with the reactivation of herpes simplex virus have also been implicated in Bell's palsy. These factors include upper respiratory tract infections, exposure to cold drafts, ultraviolet light or sunburn, emotional upset, pregnancy, menstruation and dental extraction. Recurrent mucocutaneous herpes simplex and Bell's palsy also have similar dinical courses, with peak expression within four to seven days and resolution by 14 days.

While controversy surrounds the exact agent or factor precipitating Bell's palsy, there is greater agreement on the mechanism of the nerve injury. An inciting event, such as a viral infection, initiates nerve damage by inducing an autoimmune reaction. The resultant edema within the rigid confines of the facial canal causes vascular insufficiency and hypoxia. The hypoxia, in turn, leads to more edema, perpetuating the injury.

Treatment

A primary concem in the management of Bell's palsy is eye care. Regardless of what other therapy is undertaken, dark glasses should be wom during the day, drops used to prevent drying and a bland ointment applied during sleep. Taping the eye shut is not recommended.'

Other treatments for Bell's palsy remain controversial. Some authors report that prednisone, started as soon after the onset of weakness as possible, reduces the number of patients suffering complete denervation. One treatment protocol consists of oral prednisone at 1 mg per kg per day in a divided dose. The patient is reevaluated after five or six days, and if the paralysis is incomplete, the medication is tapered over five days. If the paralysis is complete, ten more days of prednisone at 1 mg per kg per day is recommended, followed by a five-day tapering. Steroids should not be stopped abruptly, since rebound inflammation can cause further denervation.

McGovern and Estevez's have advocated the use of cromolyn sodium (Intal, Nasalcrom) as a means of preventing mast cell degranulation. This agent also interrupts the cycle of edema leading to increased pressure leading to vascular insufficiency leading to more edema. The suggested approach is intensive, calling for the inhalation of 20 mg of cromolyn sodium every two to three hours around the clock, with serial nerve excitability measurements to monitor progress. As with steroid therapy, abrupt withdrawal of treatment may lead to rebound edema. Although these authors do not provide any statistical analysis, they state that of 60 patients managed in this manner, all experienced complete recovery. These results are cited as supporting evidence for an immunologic component in the pathogenesis of Bell's palsy.

Intramuscular injections of corticotropin (ACTH, Acthar), which were advocated in the past, have been shown to be less effective than prednisone.

Other authorities 12,20,21 state that the prognosis in Bell's palsy is universally excellent regardless of whether any medical treatment is provided and that treatment should not be undertaken in light of the possible complications. They claim that no definitive clinical trials have shown a statistical advantage to the use of steroids in patients with Bell's palsy. In fact, Katusic and associates, 8while supporting the use of steroids, admit that assessing the effectiveness of any treatment is difficult in a disease with a spontaneous remission rate as high as that of Bell's palsy.

Another possible therapeutic agent is acyclovir (Zovirax), an inhibitor of viral thymidine kinase. This drug has been used in the treatment of herpes zoster facial paralysis. The Facial Nerve Disorder Committee of the American Academy of Otolaryngology-Head and Neck Surgery is preparing to implement a multicenter research trial of acyclovir.

The need for surgical decompression of the facial nerve in the treatment of Bell's palsy is another issue that remains undecided.' In certain instances, however, surgery should be considered in the management of idiopathic facial paralysis. One obvious indication would be for diagnostic evaluation when there is doubt that the palsy is truly idiopathic and when malignancy is a possibility. Such doubts should be entertained (1) when paralysis is sudden and complete, with an evoked electromyography of zero; (2) when paralysis is slowly progressive over more than three weeks; (3) when no recovery is seen after six months; (4) when persistent twitching occurs; (5) when a mass in the salivary glands or neck is present; (6) when a mass is noted between the mandible and mastoid; (7) when progression of other cranial nerve deficits occurs; (8) when branches of the facial nerve are spared, or (9) when the past history includes malignancy.

Surgery also may be indicated for protection of the eye in the acute phase of the disease. Candidates for surgical eyelid reanimation are patients who

have keratitis or who fail to respond to medical therapy with drops, ointment or a moisture chamber. Other patients who may require eyelid surgery are those with a syndrome featuring anesthesia of the cornea, dry eye and lack of Bell's phenomenon (an upward and outward deviation of the eye when the patient attempts to close the affected eyelid [Figure3l). Patients with any of these problems are at high risk for severe keratitis, corneal ulceration or comeal perforation.

The surgical procedures that may be used include suture tarsorrhaphy, lower lid tightening and reanimation of the upper eyelid by weighting with gold or spring implantation. Tarsorrhaphy should be used only as a last resort, since the technique limits vision, creates a cosmetic defect, may lead to ingrowth of the eyelashes, causing further irritation, and may even fail to protect the comea.

Other surgical reanimation techniques can be used for patients with Bell's palsy who suffer permanent complete facial paralysis. In such patients, end-to-end anastomosis of the facial nerve and ipsilateral or contralateral facial nerve grafting using sural, hypoglossal or greater auricular nerves allows good physiologic recovery if the procedures are performed within one year of the onset of symptoms. For example, in one study of eight patients undergoing end-to-end anastomosis, one patient had a superb result (volitional expression with minimal mass movement), six had excellent results (volitional expression with mass movement), and one had a poor result (no change), due to a technical error. In patients with facial paralysis persisting longer than two years, hypoglossal-to-facial nerve anastomosis, cervical nerve-muscle pedicle transposition, masseter muscle transposition, temporalis muscle transposition and free muscle implants are available. These procedures provide voluntary movement but not spontaneous facial expression. Selective neurolysis, myolysis and other static techniques can then be used to fine-tune the cosmetic result.

Physiotherapy using electric stimulation of paralyzed muscles has been widely used in the treatment of muscles denervated by many different causes. This method of treatment continues to be used despite controversy over its efficacy. In the late 1940s, it was shown to be of no benefit, and more recent data suggest that electric stimulation of denervated muscles actually slows the ingrowth of neurofibrils at the motor end plate .

Final Comment

Decisions about the type of treatment necessary for a patient with idiopathic facial weakness remain primarily in the hands of the family physician and are based on the physician's experience and each patient's presentation. The need for consultation should be considered whenever the diagnosis of Bell's palsy is in doubt, the patient's vision is at risk or the patient requests rehabititation of a permanent complete facial palsy. In addition, certain patients, such as public figures, may desire referral for testing to predict time course and level of recovery to be expected.

COPYRIGHT 1989 American Academy of Family Physicians
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