bell's palsy

Introduction

Background

Facial paralysis is a disfiguring disorder that has a great impact on the patient. Facial nerve paralysis may be congenital, neoplastic, or result from infection, trauma, toxic exposures, or iatrogenic causes. The most common cause of unilateral facial paralysis is Bell palsy, also known as idiopathic facial paralysis. Bell palsy is thought to account for approximately 60-75% of cases of acute unilateral facial paralysis.

In 1550, Fallopius noted the narrow lumen in the temporal bone through which a part of the seventh cranial nerve passes. In 1828, Charles Bell made the distinction between the fifth and seventh cranial nerves; he noted that the seventh nerve was involved mainly in the motor function of the face and the fifth nerve was concerned mainly with the sensory perception of the face.

Even today, controversy still surrounds the etiology and treatment of Bell palsy. Clinical features of Bell palsy that may help distinguish it from other causes of facial paralysis include sudden onset of unilateral facial paralysis (less than 48 hours), absence of signs and symptoms of CNS disease, and absence of signs and symptoms of ear or posterior fossa disease.

Pathophysiology

The course of the facial nerve is tortuous, both centrally and peripherally (see Media file 1).

The facial nerve nucleus lies within the reticular formation of the pons, adjacent to the fourth ventricle. The facial nerve roots include fibers from the motor, solitary, and salivatory nuclei. The nervus intermedius comprises fibers from salivatory and solitary nuclei (it contains sensory fibers from the tongue, mucosa, and postauricular skin as well as parasympathetic fibers to the salivary and lacrimal glands). The fibers of the facial nerve then course around the sixth cranial nerve nucleus and exit the pons at the cerebellopontine angle. The fibers go through the internal auditory canal along with the vestibular portion of the eighth cranial nerve. The narrowest portion of the internal auditory canal is the labyrinthine segment. This is the location that is thought to be the most common site of compression of the facial nerve in Bell palsy.

The seventh cranial nerve contains parasympathetic fibers to the nose, palate, and lacrimal glands. The preganglionic parasympathetic fibers that originate in the salivatory nucleus join the fibers from nucleus solitarius to form the nervus intermedius. These fibers then synapse with the submandibular ganglion, which has fibers that supply the sublingual and submandibular glands. The fibers from the nervus intermedius also supply the pterygopalatine ganglion, which has parasympathetic fibers that supply the nose, palate, and lacrimal glands.

The facial nerve passes through the stylomastoid foramen in the skull and terminates into the zygomatic, buccal, mandibular, and cervical branches. These nerves serve the muscles of facial expression, which include frontalis, orbicularis oculi, orbicularis oris, buccinator, and platysma. Other muscles innervated by the facial nerve include stapedius, stylohyoid, posterior belly of the digastric, occipitalis, and anterior and posterior auricular muscles. All muscles of the facial nerve are derived from the second brachial arch.

The location of injury of the facial nerve in Bell palsy is peripheral to the seventh nerve nucleus. The injury is thought to occur near or at the geniculate ganglion. If the lesion is proximal to the geniculate ganglion, the motor paralysis is accompanied by gustatory and autonomic abnormalities. Lesions between the geniculate ganglion and the origin of the chorda tympani produce the same effect except that they spare lacrimation. If the lesion is at the stylomastoid foramen, it may result in facial paralysis only.

Bell palsy is thought to be caused by edema and ischemia resulting in compression of the facial nerve in its course through the bony canal. The cause of the edema and ischemia is still being debated. In the past, cold exposure (eg, chilly wind, cold air conditioning, or driving with the car window down) were considered the only triggers to Bell palsy. Several authors believe that the herpes simplex virus (HSV) is a common cause of Bell palsy. However, studying the causal relationship between HSV and Bell palsy is difficult because of the ubiquitous nature of HSV.

In 1972, McCormick first suggested that HSV is responsible for idiopathic facial paralysis.¹ This was based on the analogy that HSV was found in cold sores, and he hypothesized that HSV may remain latent in the geniculate ganglion. Since then, autopsy studies have shown HSV in the geniculate ganglion of patients with Bell palsy. Murakami et al performed polymerase chain reaction (PCR) testing for HSV in the endoneural fluid of the seventh nerve of patients who underwent surgery for Bell palsy. Of the 14 patients, 11 were found to have HSV in the endoneural fluid.² Assuming that HSV is the etiologic agent in Bell palsy is reasonable. If this is true, then the virus is most likely to travel up the axons of the sensory nerves and reside in the ganglion cells. At times of stress, the virus will reactivate, causing local damage to the myelin.

Thus, Bell palsy may be secondary to viral, and/or autoimmune reactions causing the facial nerve to demyelinate, resulting in unilateral facial paralysis.

Frequency

United States

The annual incidence of Bell palsy is approximately 23 cases per 100,000 persons. The right side is affected 63% of the time. Persons with diabetes have a 29% higher risk of being affected by Bell palsy than persons without diabetes. Thus, measuring blood glucose levels at the time of diagnosis of Bell palsy may detect undiagnosed diabetes.

International

The highest incidence was found in a study in Seckori, Japan, in 1986 and the lowest incidence was found in Sweden in 1971. Most population studies generally show an annual incidence of 15-30 cases per 100,000 population.

Mortality/Morbidity

• Most patients who suffer from Bell palsy have neurapraxia or local nerve conduction block. These patients are likely to have a prompt and complete recovery of the nerve. Patients with axonotmesis, with disruption of the axons, have a fairly good recovery but it is usually not complete. The risk factors thought to be associated with a poor outcome in patients with Bell palsy include (1) age greater than 60 years, (2) complete paralysis, and (3) decreased taste or salivary flow on the side of paralysis (usually 10-25% compared to the patient's normal side). Other factors thought to be associated with poor outcome include pain in the posterior auricular area and decreased lacrimation.
• Patients generally have a good prognosis; approximately 80-90% of patients recover without noticeable disfigurement within 6 weeks to 3 months. Patients aged 60 years or older have an approximately 40% chance of complete recovery and have a higher rate of sequelae. Patients younger than 30 years have only a 10-15% chance of less than complete recovery and sequelae. If no recovery occurs by 4 months, then the patient is more likely to have sequelae from the disease, which include synkinesis, crocodile tears, and rarely hemifacial spasm.
• Synkinesis is an abnormal contracture of the facial muscles while smiling or closing the eyes. It may be mild and result in slight movement of the chin when the patient blinks, eye closure with smiling, or contracture around the mouth while blinking. Crocodile tears are observed; patients shed tears while they eat.
• Facial spasm is a very rare complication of Bell palsy. It occurs as tonic contraction of one side of the face. Spasms are more likely to occur during times of stress or fatigue and may occur during sleep. This condition may occur secondary to compression of the root of the seventh nerve by an aberrant blood vessel, tumor, or demyelination of the nerve root. It occurs most commonly in the fifth and sixth decades of life, and sometimes the etiology is not found. The presence of progressive facial hemispasm with other cranial nerve findings indicates a possibility of a brainstem lesion.
• Diabetic patients are 30% more likely than nondiabetic patients to have only partial recovery; recurrence of Bell palsy is also more common among diabetic patients.
• Bell palsy accounts for only 23% of bilateral facial paralysis. The majority of patients with bilateral facial palsy have Guillain-Barré syndrome (GBS), sarcoidosis, Lyme disease, meningitis (neoplastic or infectious), or bilateral neurofibromas (in patients with neurofibromatosis type 2).
• Bell palsy recurs in 10-15% of patients. It may recur on the ipsilateral or contralateral side of the initial palsy. Recurrence usually is associated with a family history of recurrent Bell palsy. Approximately 30% of patients with recurrent ipsilateral facial palsy were found to have tumors of the seventh nerve or parotid gland. Patients with recurrent ipsilateral facial palsy should undergo MRI or high-resolution CT scan to rule out neoplastic or inflammatory (eg, multiple sclerosis, sarcoidosis) cause of recurrence.

Sex

• Bell palsy appears to affect the sexes equally. However, young women aged 10-19 years are more likely to be affected than men in the same age group.
• Pregnant women have a 3.3 times higher risk of being affected by Bell palsy than nonpregnant women; Bell palsy occurs most frequently in the third trimester.

Age

The lowest incidence is found in persons younger than 10 years and the highest incidence in persons aged 60 years or older.

Clinical

History

Bell palsy is a diagnosis of exclusion. The diagnosis must be made on the basis of a thorough history and physical examination and use of diagnostic testing when necessary.

• Symptoms of Bell palsy
• Acute onset of unilateral upper and lower facial paralysis (over a 48-h period)
• Posterior auricular pain
• Decreased tearing
• Hyperacusis
• Taste disturbances
• The paralysis must include the forehead and lower aspect of the face. The patient may report inability to close the eye or to smile on the affected side. He or she also may report increased saliva on the side of the paralysis. If the paralysis involves only the lower portion of the face, a central cause should be suspected (ie, supranuclear). If the patient complains of contralateral weakness or diplopia in conjunction with the supranuclear facial palsy, a stroke or intracerebral lesion should be strongly suspected.
• Half of the patients affected with Bell palsy may complain of posterior auricular pain. Ask the patient if he or she has experienced trauma, which may account for the pain and facial paralysis.
• One third of patients may experience hyperacusis in the ear ipsilateral to the paralysis, which is secondary to weakness of the stapedius muscle.
• One sixth of patients experience decreased lacrimation.
• Many patients report numbness on the side of the paralysis. Some authors believe that this is secondary to involvement of the trigeminal nerve, whereas other authors argue that this symptom is probably due to lack of mobility of the facial muscles and not lack of sensation.
• If a patient has gradual onset of facial paralysis, weakness of the contralateral side, or history of trauma or infection, other causes of facial paralysis must be strongly considered. Patients who have bilateral facial palsy must be evaluated for GBS, Lyme disease, and meningitis.
• If a patient is from the Northeast, Lyme disease should be considered as a cause of facial paralysis, and serologic testing should be performed. Approximately 5-10% of untreated Lyme patients may have a peripheral seventh nerve palsy. For related information, see Medscape's Lyme Disease Resource Center.
• Recurrent ipsilateral facial paralysis must raise the suspicion of a tumor of the seventh nerve or parotid gland. If the patient reports sudden onset of hearing loss and severe pain with the onset of facial paralysis, Ramsay Hunt syndrome must be considered.
• Symptoms associated with seventh nerve neoplasm include slowly progressive paralysis, facial hyperkinesis, severe pain, recurrent palsy, and other cranial nerve involvement. Cerebellopontine tumors may affect the seventh, eighth, and fifth cranial nerves simultaneously. Patients with a progressive paralysis of the facial nerve lasting longer than 3 weeks should be evaluated for neoplasm.

Physical

• Initial inspection of the patient demonstrates flattening of the forehead and nasolabial fold on the side affected with the palsy.
• When the patient is asked to raise the eyebrows, the side of the forehead with the palsy will remain flat.
• When the patient is asked to smile, the face becomes distorted and lateralizes to the side opposite the palsy.
• The patient is not able to close the eye completely on the affected side. On attempted eye closure, the eye rolls upward and inward on the affected side. This is known as Bell phenomenon and is considered a normal response to eye closure.
• A careful examination of the head, ears, eyes, nose, and throat (HEENT) must be carried out in all patients with facial paralysis.
• The external auditory canal must be inspected for vesicles, injection, infection, or trauma.
• The patient may have decreased sensation to pinprick in the posterior auricular area.
• The patient who has paralysis of the stapedius muscle will report hyperacusis.
• Bell phenomenon is observed on attempted eye closure.
• With weakness/paralysis of the orbicularis oculi muscle (facial nerve innervation) and normal function of the levator muscle (oculomotor nerve innervation) and Mueller muscle (sympathetic innervation), eye closure may be partial or absent. The tear reflex may also be absent in many cases of Bell palsy. For these reasons the patient may have decreased tearing and susceptibility to corneal abrasion and dryness of the eye. The patient may appear to have loss of corneal reflex on the affected side; however, the contralateral eye blinks when testing the corneal reflex on the affected side.
• A careful oral examination must be performed.
• Taste and salivation are affected in many patients with Bell palsy.
• Taste may be assessed by holding the tongue with gauze and testing each side of the tongue independently with salt, sugar, and vinegar. The mouth must be washed after testing with different substances. The affected side has decreased taste as compared to the normal side.
• Careful neurologic examination is necessary in patients with facial paralysis. A neurologic abnormality warrants neurologic referral and further testing such as MRI of the brain, lumbar puncture, and electromyography (EMG) where appropriate.

Differential Diagnoses

Acute Inflammatory Demyelinating Polyradiculoneuropathy	Low-Grade Astrocytoma
Amyloid Angiopathy	Lyme Disease
Anterior Circulation Stroke	Meningioma
Arsenic	Meningococcal Meningitis
Basilar Artery Thrombosis	Möbius Syndrome
Benign Skull Tumors	Multiple Sclerosis
Brainstem Gliomas	Neurofibromatosis, Type 2
Cerebral Aneurysms	Neurosarcoidosis
Guillain-Barre Syndrome in Childhood	Neurosyphilis
Intracranial Hemorrhage	Tuberculous Meningitis

Other Problems to Be Considered

Basal skull fractures
Barotrauma
Botulism
Carcinomatosis
Carotid disease and stroke
Diphtheria
Facial injuries
Forceps delivery
HIV
Iatrogenic (as in otologic, neurotologic, skull base, or parotid surgery)
Idiopathic
Infection
Intratemporal internal carotid artery aneurysm
Lyme disease
Malignant otitis externa
Meningitis
Mycoplasma pneumonia
Mumps
Parotid tumor
Ramsay Hunt syndrome
Sarcoma
Teratoma
Tetanus
Thalidomide exposure
Trauma
Toxic
Vascular
Wegener vasculitis

Workup

Laboratory Studies

• In areas where Lyme disease is endemic, Lyme titers (IgM and IgG) should be obtained.
• Blood glucose or hemoglobin A1c may be obtained to determine if the patient has undiagnosed diabetes.
• Serum titres (IgM and IgA) for Mycoplasma pneumoniae may be obtained. A study in Germany measured titres in patients with Bell palsy and found that several patients had elevated titres to M pneumoniae, and only 2 of those who tested positive had respiratory symptoms.³  
• Serum titers for HSV may be obtained, but this is usually not helpful owing to the ubiquitous nature of this virus.

Imaging Studies

• If the history and physical examination lead to a diagnosis of Bell palsy, then immediate imaging is not necessary.
• Imaging is not required because most patients with Bell palsy improve within 8-10 weeks. If the paralysis does not improve or worsens, imaging may be useful.
• The MRI of patients with Bell palsy may show enhancement of the seventh nerve at, or near, the geniculate ganglion. However, if the paralysis progresses over weeks, the possibility is high of a neoplasm compressing the seventh cranial nerve. Tumors that compress or involve the seventh cranial nerve include schwannoma (most common), hemangioma, meningioma, and sclerosing hemangioma.
• MRI is preferred for imaging the cerebellopontine angle.
• If the patient has a history of trauma, CT scan of the temporal bone may be required.
• If the patient has a palpable parotid mass, imaging may be necessary.

Other Tests

• The following tests may be performed in the office setting. However, they require both the patient's and physician's time. They may be helpful in assessing the extent of the damage to the seventh nerve.
• The stethoscope loudness test may be used to assess the functioning of the stapedius muscle. The patient wears the stethoscope, and the activated tuning fork is placed at the bell of the stethoscope. The loud sound will lateralize to the side of the paralyzed stapedius muscle
• The Schirmer blotting test may be used to assess tearing function. The use of benzene will stimulate the nasolacrimal reflex, and the degree of tearing can be compared between the paralyzed and normal sides.
• Salivary flow also may be tested. The physician places a small catheter into both the paralyzed and normal submandibular glands. The patient is then asked to suck on a lemon, and the salivary flow is compared between the 2 sides. The normal side is the control.
• Useful tests for evaluation of the function of the facial nerve include nerve conduction testing and EMG.
• These tests may aid in assessing the outcome of a patient who has persistent and severe Bell palsy. This test is most useful when performed 3-10 days after the onset of paralysis.
• Nerve conduction responses are abnormal if a difference of 50% in amplitude between the paralyzed and normal side is detected; a difference of 90% between the 2 sides suggests a poorer prognosis.
• May et al demonstrated that prognosis may be favorable if the motor amplitude of the affected side was greater than 25% of that of the normal side. An incomplete recovery was observed in patients whose results demonstrated less than 25% amplitude on the paralyzed side.⁴
• Blink reflexes can be used to measure conduction across the involved segment but they are commonly absent in Bell palsy.
• Brainstem auditory-evoked response (BAER) may be obtained in patients with peripheral seventh nerve lesions and other neurologic involvement.
• BAER measures the transmission of response through the brain stem and is effective in detecting, notably, retrocochlear lesions.
• Hendrix and Melnick evaluated BAER of 17 patients with Bell palsy. They found no evidence of retrocochlear lesions of the auditory system in any of their patients with Bell palsy.⁵
• In another study by Shannon et al, BAER was recorded in 27 patients with Bell palsy; only 6 patients had prolonged brainstem transmission but normal auditory function.⁶
• These studies were small and do not support routine use of BAER in patients with Bell palsy. However, when a patient presents with multiple cranial neuropathies, ie, of CN VII and VIII, BAER may be useful.

Histologic Findings

A review of 12 autopsy cases of patients with Bell palsy was summarized in Peter Dyck's Peripheral Neuropathy.⁷ This stated that most cases showed inflammatory changes around the mastoid cells and walls of the arteries. The most common site of involvement was the geniculate ganglion.

Surgical findings described constriction of the nerve at the stylomastoid foramen with swelling of the nerve itself. Microscopic findings showed an inflammatory reaction with infiltration of macrophages on the nerve.

Treatment

Medical Care

In general, persons with true Bell palsy have an excellent prognosis. Thus, treatment of Bell palsy is still controversial, because spontaneous recovery is fairly common. The goals of treatment are to improve function of the facial nerve and reduce neuronal damage. Many issues must be addressed in treating patients with Bell palsy. The most important consideration is the onset of symptoms. Treatment may be considered for patients who have the onset of paralysis within 1-4 days of the initial office visit.

The American Academy of Neurology published a practice parameter in 2001 stating that steroids are probably effective and acyclovir (with prednisone) is possibly effective for treatment of Bell palsy. In October 2007, a large double-blinded, placebo-controlled, randomized Scottish study was published.⁸  The results showed that early treatment with prednisolone alone, and not combined with acyclovir, is effective for Bell palsy. Any recommendation on facial decompression surgery had insufficient evidence.

• The most widely accepted treatment for Bell palsy is corticosteroids. However, the use of steroids is still controversial because most patients recover without treatment.
• The recommended dose of prednisone is 1 mg/kg or 60 mg/d for 6 days, followed by a taper, for a total of 10 days.
• Many trials have been carried out to study the efficacy of prednisone in Bell palsy. Early studies had small numbers of patients and variable outcomes. In 1972, Adour et al conducted a large, controlled clinical trial that found that 89% of patients treated with prednisone had full recovery compared with 64% of patients treated with placebo.⁹
• A large Scottish study published in 2007 included 551 patients that were randomized to prednisolone and acyclovir, prednisolone alone, acyclovir alone, and placebo. At 3 months, 83% in the prednisolone group and 63.6% in the placebo group had recovered facial function. At 9 months, 94.4% in the prednisolone group and 81.6% in the placebo group had recovered facial function. The group that was treated with acyclovir did not have a significant improvement in facial function compared with the placebo group. In the double placebo group, 85% had full recovery at 9 months.⁸
• When using corticosteroids for the treatment of Bell palsy, caution should be used in patients with tuberculosis, peptic ulcer disease, diabetes mellitus, renal or hepatic dysfunction, or malignant hypertension.
• Quant et al conducted a meta-analysis of published studies from 1984 to January 2009 to compare use of corticosteroids plus antiviral agents with corticosteroids alone on degree of facial muscle recovery in patients with Bell palsy. Six trials (representing pooled data of 1145 patients) were examined and included 574 patients who received corticosteroids alone and 571 patients who received corticosteroids and antiviral agents. The analysis showed no improved benefit for Bell palsy with use of corticosteroids plus antivirals compared with corticosteroids alone (odds ratio 1.50; 95% confidence interval, 0.83-2.69; P=0.18). The authors suggest the routine use of antivirals is not warranted; however, future studies should improve diagnostic efforts to identify herpes virus as a potential etiology. Additionally, newer antiviral agents may prove more beneficial than older antiviral agents used in the studies analyzed.¹⁰
• Recent guidelines suggest that the use of acyclovir for the treatment of Bell palsy is only possibly effective. They suggest that this agent alone is not effective in facial recovery. The Scottish study suggested that prednisolone, and not acyclovir, is useful for facial recovery in Bell palsy. The dose of acyclovir is 400 mg PO 5 times per day. The dose of valacyclovir, when used with prednisolone, is 1 g/d for 5 days. This combination was recently proven to be effective in a Japanese study.
• A prospective randomized trial with 101 patients comparing prednisone and acyclovir demonstrated that the prednisone group had a better clinical recovery.¹¹ In another prospective randomized trial with 99 patients, prednisone monotherapy was compared with the combination of prednisone and acyclovir. This study demonstrated that combination therapy was more effective in preventing nerve degeneration as measured by electrodiagnostic tests.¹²
• In April 2007, a Japanese randomized prospective study on 221 patients with Bell palsy was published. It showed significant improvement in facial function using both prednisone and valacyclovir therapy as compared with those who used prednisone alone. This improvement was noted in those who had severe to complete facial palsy.¹³
• Whether to use prednisone alone or combination therapy is left to the discretion of the treating physician.
• That eye care is imperative in Bell palsy is accepted universally. The patient's eye is at risk for drying, corneal abrasion, and corneal ulcers. Eye care includes artificial tears for use during the day as well as eyeglasses or shields. At night, eye lubricants may be used. If artificial tears are not effective during the daytime, then lubricants may be used; however, they may cause blurring of vision.

For other views on treatment of Bell palsy, see Medscape's CME activity, Evidence-Based Management of Bell's Palsy: A Best Evidence Review.

Surgical Care

Surgery for Bell palsy is controversial. In the past, surgical decompression of the facial nerve was considered for patients whose facial muscles demonstrated less than 90% of normal activity on electrophysiologic studies. Surgical decompression of the facial nerve involves a middle fossa craniotomy with an extradural approach. However, recent trials suggest this is not beneficial in patients with Bell palsy.

Consultations

If the initial impression based on the history and physical examination is not Bell palsy, then consultation with a neurologist or otolaryngologist is needed. For example, the patient who has facial palsy and pain and in whom the ear, nose, and throat examination does not show auricular vesicles (as in Ramsay Hunt syndrome), then consultation with an otolaryngologist should be made. These patients should be evaluated for malignancy of the seventh nerve.

• If the paralysis persists for several months, consultation with a neurologist or otolaryngologist should be sought.
• Patients who report persistent dry eye or painful eye should be referred to an ophthalmologist.

·         Medication

·         The goals of pharmacotherapy are to reduce morbidity and prevent complications.

·         Corticosteroids

·         Prednisone can be used but has many adverse effects including fluid retention, hypokalemia, myopathy, peptic ulcer, headache (pseudotumor), menstrual irregularities, cataracts, glaucoma, and manifestation of latent diabetes mellitus. Signs of infection may also be masked in patients taking prednisone. Physicians should use caution when using prednisone in patients with the aforementioned conditions.

·          

·         Prednisone (Deltasone, Orasone, Sterapred)

·         Glucocorticoid absorbed readily from GI tract. It has anti-inflammatory and immune-modulating effects, and profound and varied metabolic effects.

• Dosing

Adult

1 mg/kg or 60 mg PO qd for 7 d followed by taper for total of 10 d

Pediatric

1 mg/kg PO qd for 6 d followed by taper for total of 10 d

·         Interactions

Coadministration with estrogens may decrease clearance; concurrent use with digoxin may cause digitalis toxicity secondary to hypokalemia; phenobarbital, phenytoin, and rifampin may increase metabolism of glucocorticoids (consider increasing maintenance dose); monitor for hypokalemia with coadministration of diuretics

·         Contraindications

Documented hypersensitivity; viral infection, peptic ulcer disease, hepatic dysfunction, connective tissue infections, and fungal or tubercular skin infections; GI bleeding or ulceration

·         Precautions

Pregnancy

B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals

Precautions

Abrupt discontinuation of glucocorticoids may cause adrenal crisis; hyperglycemia, edema, osteonecrosis, myopathy, peptic ulcer disease, hypokalemia, osteoporosis, euphoria, psychosis, myasthenia gravis, growth suppression, and infections may occur with glucocorticoid use

Antiviral medication

Acyclovir has been used in the treatment of Bell palsy in combination with prednisone or used alone in patients who cannot take prednisone.

Acyclovir (Zovirax)

Prodrug activated by phosphorylation by virus-specific thymidine kinase that inhibits viral replication. Herpes virus thymidine kinase (TK), but not host cells TK, uses acyclovir as a purine nucleoside, converting it into acyclovir monophosphate, a nucleotide analogue. Guanylate kinase converts the monophosphate form into diphosphate and triphosphate analogues that inhibit viral DNA replication.

Has affinity for viral thymidine kinase and once phosphorylated causes DNA chain termination when acted on by DNA polymerase. Inhibits activity of both HSV-1 and HSV-2. Patients experience less pain and faster resolution of cutaneous lesions when used within 48 h from rash onset. May prevent recurrent outbreaks. Early initiation of therapy is imperative.

Has been used in the treatment of Bell palsy in combination with prednisone or used alone in patients who cannot take prednisone.

·         Dosing

Adult

800 mg PO 5 times/d for 10 d

Pediatric

<2 years: Not established
>2 years: 20 mg/kg for 10 d

·         Interactions

Concomitant use of probenecid or zidovudine prolongs half-life and increases CNS toxicity of acyclovir

·         Contraindications

Documented hypersensitivity

·         Precautions

Pregnancy

B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals

Precautions

Caution in renal failure or when using nephrotoxic drugs

Valacyclovir (Valtrex)

Prodrug rapidly converted to the active drug acyclovir. More expensive but has a more convenient dosing regimen than acyclovir

·         Dosing

Adult

2 g PO q12h for 1 day

Pediatric

Not established

·         Interactions

Probenecid, zidovudine, or cimetidine coadministration prolongs half-life and increases CNS toxicity of valacyclovir

.

·         Dosing

·         Interactions

·         Contraindications

·         Precautions

Adult

2 g PO q12h for 1 day

Pediatric

Not established

·         Interactions

Probenecid, zidovudine, or cimetidine coadministration prolongs half-life and increases CNS toxicity of valacyclovir

·         Contraindications

Documented hypersensitivity

·         Precautions

Pregnancy

B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals

Precautions

Caution in renal failure (decrease dose) and coadministration of nephrotoxic drugs; associated with onset of hemolytic uremic syndrome

Follow-up

Further Outpatient Care

• If the paralysis is not resolved or is progressing to complete paralysis, a thorough neurologic and HEENT examination should be performed to rule out neoplastic causes of seventh nerve palsy.
• The patient should be monitored if the initial EMG shows the involved facial muscles to have less than 25% of the function of the normal side.
• If the residual paralysis is severe, the patient should be referred for counseling.

Complications

• Approximately 30% of patients with Bell palsy experience sequelae of the paralysis, which include incomplete motor recovery, incomplete sensory regeneration, and parasympathetic impairment.
• Incomplete motor recovery may manifest as oral incompetence or epiphora.
• Incomplete sensory recovery may result in dysgeusia (impairment of taste) or ageusia (loss of taste).
• Parasympathetic impairment causes aberrant function of lacrimal glands, which manifests as crocodile tears; patients report shedding tears while eating.

Prognosis

• The natural course of Bell palsy varies from early complete recovery to substantial nerve injury resulting in persistent paralysis and synkinesis.
• One third of patients regain complete recovery of facial motor function without sequelae.
• One third of patients have incomplete recovery of facial motor function. These patients do not have any noticeable abnormalities.
• The remainder of patients have permanent neurological and cosmetic abnormalities.

Patient Education

• To prevent corneal abrasions, the patient should be educated concerning eye care.
• They also should be encouraged to do facial muscle exercises using passive range of motion as well as actively closing their eyes and smiling.
• For excellent patient education resources, visit eMedicine's Brain and Nervous System Center. Also, see eMedicine's patient education article Bell Palsy.

Miscellaneous

Medicolegal Pitfalls

In most cases, the diagnosis of Bell palsy is straightforward as long as the patient underwent a thorough history and physical examination. Failure to recognize structural, infectious, or vascular lesions leading to seventh nerve damage may result in further deterioration of the patient's condition. For example, if other cranial nerve, motor, or sensory symptoms were present at the time, then treatable or preventable nervous system diseases should be sought. These may include stroke, GBS, basilar meningitis, or cerebellar pontine angle tumor.