We dont know what exactly causes Bells palsy. We do know that it is an idiopathic paresis or paralysis of the facial nerve (cranial nerve VII), that it comes on quickly, and that it can resolve within months. We know that a delayed recovery is cause for concern. In recent years, weve learned from medical research that the herpes simplex virus may be implicated.
1. Full Bells palsy involvement affecting the left side of the face.
All patients with Bells palsy are at risk for exposure keratitis, corneal scarring or perforation and possible vision loss. So as primary care practitioners, we must possess a thorough knowledge of this common facial nerve palsy and its management. This clinical review updates the latest thinking on Bells palsy.
Bells palsy comes on quickly, and has no other identifiable etiology such as infection, neoplasm or trauma. It involves the entire side of the faceforehead, eyelids, facial muscles of expression and mouthan important sign when differentiating Bells palsy from a true stroke.
If the upper face appears spared, suspect a supranuclear or upper-motor neuron lesion from a stroke or tumor. A unilateral lesion in the cortex or supranuclear pathway spares the frontalis, orbicularis oculi and corrugator muscles, resulting in normal eyelid closure and forehead wrinkling. A lower-motor neuron lesion such as that seen in Bells palsy results in complete unilateral involvement.
Evidence implicating herpes simplex virus (HSV) in Bells palsy continues to accumulate. This is based on the high frequency of elevated viral antibody titers as well as elevated levels of interferon first identified in patients with Bells palsy in the mid-1970s.1 A more recent study found that 79% of patients with idiopathic facial paralysis demonstrated DNA fragments of HSV in the endoneurial fluid and posterior auricular muscle biopsy specimens, providing the strongest link yet between herpes simplex infection and Bells palsy.2 The same study found no herpes simplex DNA fragments in control patients or in those with facial paralysis from other causes, such as Ramsay Hunts syndrome, which is caused by the varicella-zoster virus.
This study may have significant implications for how doctors manage Bells palsy with antiviral and anti-inflammatory agents. Initiation of antiviral agents such as Zovirax (acyclovir, Glaxo SmithKline) at the first signs of disease probably would not cure Bells palsy. Thats because the nerve damage has already occurred by the time facial paralysis surfaces. However, such treatment may lessen the effects of paralysis and shorten the duration of the symptoms.
Triggers associated with Bells palsy are also known to reactivate herpes simplex virus. Upper respiratory tract infection, fever, dental extraction, menstruation or exposure to cold might reactivate latent herpes virus in the facial nerve ganglia.2 After reactivation, the virus destroys ganglion cells and spreads into the endoneurial fluid. The virus also infects Schwann cells, leading to demyelinization and inflammation of the facial nerve.3 The facial nerve then becomes compressed and ischemic in its narrow course through the temporal bone of the skull. Conduction block and nerve degeneration may result.4 Magnetic resonance imaging (MRI) has confirmed this inflammatory response in patients with Bells palsy.5
2. Loss of forehead furrowing in left-sided Bells palsy.
Bells palsy usually occurs rapidly. It can progress, but reaches maximal involvement in two to three weeks.8,9 Men and women are affected equally, and even though age may not be a factor, most cases occur in individuals ages 20-40.9 Bells palsy affects the left and right sides of the face with equal frequency.10 There is a higher incidence of the condition during pregnancy, especially with concurrent preeclampsia.11 To date, the literature does not indicate a strong familial predilection to Bells.
Recovery begins within three weeks of maximal onset in 85% of cases, though severe cases can take up to six months to resolve.8,9,12 The final prognosis is best when function returns quickly. A delayed recovery increases the risk of permanent deficits, which may consist of residual weakness, tonic muscle contracture, synkinesis, spasms or gustatory lacrimation (crocodile tears). Risk factors that seem to raise the risk of incomplete recovery include hypertension, diabetes, decreased tearing, recurrent or complete paralysis, facial pain and age past 60.13,14
The Clinical Work-up
Subjectively, the patient may report drooling after brushing his or her teeth or when drinking, an asymmetrical appearance of the mouth in the mirror, an inability to whistle or blink one eye, with excessive tearing in the involved eye, facial numbness or pain (especially behind the ear), and an altered sense of taste or hearing.4,8
Because Bells palsy is a diagnosis of exclusion, you must first rule out an upper motor neuron lesion from a stroke, tumor or intracranial hemorrhage. Bells palsy will affect the entire side of the face. The paralysis is pronounced both in the forehead and the lower face. It also causes difficulty in closing the eye. A more serious condition would manifest fewer signs of paralysis.
Other signs of a more serious condition are: anisocoria, slurred speech, change in gait, inability to hold objects, weakness of an arm or leg, headache, diplopia, difficulty in swallowing or decreased sense of taste.4 If examination of the ear reveals a painful vesicular rash, then herpes-zoster infection (Ramsay Hunts syndrome) is the cause of the facial palsy; treatment with an oral antiviral agent such as Zovirax is indicated. Bilateral facial palsy with a history of a tick bite indicates Lyme disease, in which case oral antibiotics are indicated.
Further ocular and facial findings of Bells palsy include drooping of the corner of the mouth, loss of distinction of facial creases and skin folds, widened palpebral fissure, inability to close the eyelids and unfurrowed forehead (figure 2). Because the lower eyelid sags and the punctum falls away from the conjunctiva, tears spill over the cheek (epiphora).
Your ocular evaluation should include a test for corneal sensitivity with a cotton wisp. The patient with Bells palsy feels the sensation but does not blink. If the sensation to cotton wisp testing is not the same in both eyes, then suspect involvement of the trigeminal nerve or CN V.
Its also important to evaluate the extraocular muscles and systemic muscle balance in the work-up of a Bells palsy patient. Any evidence of nystagmus, eye muscle imbalance with the subjective complaint of diplopia, or limb paralysis or weakness suggests an abnormality of the brain stem or the subarachnoid space, where the cranial nerves are close together.4 Evaluate the involved eye for an adequate Bells phenomenon: the upward rolling of the globe during forced eyelid closure. A poor Bells phenomenon increases the chance of exposure keratopathy.
Use the slit lamp to examine the integrity of the corneal epithelium, and perform fluorescein or rose bengal staining at each office visit. Because the facial nerve supplies parasympathetic impulses to the lacrimal gland, many Bells palsy patients will have poor tear quality and volume.15 Significant impairment of lacrimal gland function exists if Schirmer testing reveals a 30% reduction in tearing on the involved side compared with the uninvolved side.16
3. Lagophthalmos from incomplete eyelid closure (top). Note good Bells phenomenon. 4. Taping of lower and upper eyelids achieves more complete closure.
In typical Bells palsy cases, more sophisticated testing such as MRI, computed tomography scan, electromyography, electroneuronography, nerve conduction and maximal nerve stimulation are not necessary. Imaging studies are indicated when the history or physical examination turns up suspicious findings or when facial movement does not recover within six months.
Because patients with complete facial paralysis have a poor clinical outcome, electrophysiologic testing would help in identifying those who may be good candidates for surgical facial nerve decompression. Successful release of facial nerve entrapment requires decompression of the meatal foramen, labyrinthine segment and geniculate ganglion via the middle cranial fossa approach. Results of a 15-year, prospective, multicenter trial demonstrated that middle cranial fossa decompression was superior to steroid-only treatment in patients.18
Management and Surgery
Exposure of the cornea due to Bells palsy can cause serious damage, so monitoring corneal integrity and appropriate timely intervention is essential. Also, advise patients about the risks of corneal exposure, and instruct them to instill non-preserved artificial tears hourly while awake and ophthalmic lubricating ointments at bedtime. The patient may manually close the eyelids on the involved side whenever the eye feels irritated or burns.
If lagophthalmos is significant, the patient can use transparent medical grade tape to lower the upper lid and raise the lower lid to narrow the palpebral aperture. Have the patient apply the end of the tape to the lateral aspect of the lower lid, with the upper edge about a quarter inch below the lashes, then pull the tape up laterally to secure it to the orbital rim. Then the patient should place a crescent-shaped piece of tape so that it overrides the tarsal fold in the upper lid (figures 3 and 4).17
Patients who already wear glasses can obtain additional humidification by adding side and top shields to the spectacle frame, thus forming a chamber to hold in moisture.4,9 In more severe cases in which eyelid function is markedly reduced, punctal plugs can increase the lacrimal lake, as can thick, low-water content contact lenses.15
Those patients who proceed to develop corneal damage despite appropriate conservative therapy need surgery to reanimate their paralyzed eyelids. The most vulnerable patient is one who manifests the BAD syndromethat is, lacks the Bells phenomenon, but has corneal Anesthesia and Dry eye.17
One surgical approach to achieve temporary or permanent lid closure involves implantation of a gold weight in the upper eyelid.19 Gold weights range in size from 0.6-1.6g in 0.2g increments. The surgeon implants the weight through a central eyelid crease incision, then sutures it into the upper tarsal plate after reflecting the overlying orbicularis oculi muscle. This approach offers many benefits: It creates a natural blink, is cosmetically acceptable while in place, has a low extrusion rate, leaves minimal scarring, and is removable when the facial palsy resolves.4
Another approach to achieving complete upper eyelid ptosis involves injecting Botox (botulinum to
5. Successful partial tarsorrhaphy.
In cases that involve severe corneal decompensation, a partial tarsorrhaphysurgically suturing the upper and lower eyelids partially togethermay be indicated (figure 5). This procedure is reversible, but it has a few drawbacks. It can limit visual field, cause cosmetic eyelid deformation and still leave the cornea vulnerable to occasional breakdown.4,17
The Corticosteroid Controversy
There exists significant controversy as to whether oral corticosteroid therapy is indicated in the treatment of Bells palsy. The Quality Standards Subcommittee of the American Academy of Neuro-logy has issued an evidence-based review that found that steroids probably do benefit patientsif the patient initiates treatment within two weeks of onset of symptoms.22
The recommended dosing is prednisone 1mg/kg of body weight daily (60mg/day maximum) for seven days, split into twice-daily dosing, then tapered over a subsequent three days.6,8,9
Oral prednisone is most beneficial in patients with pain and complete paralysis. The medicine appears to decrease pain and the incidence of autonomic synkinesis, hasten recovery time, and may prevent partial denervation.6,9,15
Theory holds that steroids decrease the virally mediated inflammatory response that results in nerve entrapment. However, treatment must begin promptly for maximal efficacy.23
Also, the implications of herpes simplex in Bells palsy suggest that an oral antiviral agent would be beneficial in these patients.22,24 Even more favorable outcomes have been achieved in patients who received both an oral antiviral agent and oral prednisone.25 The antiviral agents used are Zovirax 400mg five times daily for 10 days, Valtrex (valacyclovir, Glaxo SmithKline) 500mg tid for seven days, or Famvir (famciclovir, Novartis) 500mg tid for seven days. The patient should start taking the antiviral agent within the first three days of symptom onset.23,25
In approximately 30% of Bells palsy cases, recovery is not complete, and various stigmata of axonal degeneration appear. Facial nerve misdirection from aberrant regeneration may lead to a jaw-wink presentation (eye blink with jaw movement) or excessive lacrimation with chewing, also known as crocodile tears.6,15 The latter may occur in as many as 10% of recovering facial palsy patients.26
Other stigmata include eyelid weakness, involuntary muscle spasms or contractures of the eyelids or facial muscles, and facial myokymia (involuntary muscle twitching).6,15,27 Botulinum type A toxin injections have been extremely useful in managing all these problems.
While we may not be certain of what exactly causes Bells palsy, by staying current on the literature and clinical research we can minimize its effects and manage the patients who suffer from it. And by knowing the differential diagnosis, role of antiviral and corticosteroid therapy, and the need for surgical intervention, we can improve outcomes in these patients.
Dr. Skorin, a contributing editor of Review of Optometry and nationally known lecturer, is staff ophthalmologist at Albert Lea Eye ClinicMayo Health System, Albert Lea, Minn.
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