Bell's palsy

Bell's palsy
ICD-10	G51.0
ICD-9	351.0
DiseasesDB	1303
MedlinePlus	000773
eMedicine	emerg/56
MeSH	D020330

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Overview

Bell's palsy (or facial palsy) is characterised by facial drooping on the affected half, due to malfunction of the facial nerve (VII cranial nerve), which controls the muscles of the face. Named after Scottish anatomist Charles Bell, who first described it, Bell's palsy is the most common acute mononeuropathy (disease involving only one nerve), and is the most common cause of acute facial nerve paralysis. The paralysis is of the infranuclear/lower motor neuron type. Bell’s palsy affects about 40,000 people in the United States every year. It affects approximately 1 person in 65 during a lifetime. Until recently, its cause was unknown in most cases, but it has now been related to both Lyme disease and Herpes Zoster.

Epidemiology

The annual incidence rate is between 13 and 34 cases per 100,000 population. There is no race, geographic, or gender predilection. The risk is three times greater during pregnancy, especially in the third trimester or in the first postpartum week. Diabetes is present in about 5 to 10 percent of patients.

Etiology

Many cases likely due to Herpes Simplex Virus (HSV) reactivation

Infectious causes

Herpes simplex virus activation is the likely cause of Bell's Palsy in most cases.

Herpes Zoster may be the second most common associated viral infection.

Cytomegalovirus

Epstein Barr virus

Adenovirus

Rubella virus

Mumps

Influenza B

Coxsackievirus

Rickettsial infection

Ehrlichiosis

Non-infectious causes

Inactivated intranasal influenza vaccine that was introduced and since withdrawn from the market in Switzerland

Genetic predisposition in some cases

Ischemia of the facial nerve

Tumors and compression of the facial nerve

Temporal bone fracture

Systemic Lupus Erythematosus (SLE)

Sarcoidosis

Histopathology

The facial nerve has a thickened, edematous perineurium with a diffuse infiltrate of inflammatory cells between nerve bundles and around intraneural blood vessels.

The ppearance similar to that found with Herpes Zoster infection, consistent with an inflammatory and possibly an infectious cause

Peripheral versus central lesions

Sparing of the forehead muscles is suggestive of a central (upper motor neuron) lesion because of bilateral innervation to this area.

However, it does not exclude a peripheral site of pathology in all cases.

History and Symptoms

Sudden onset, usually over hours, of unilateral facial paralysis(maximal symptoms by 48 hours)

• Eyebrow sagging with inability to close the affected eye
• Nasolabial fold flattening with mouth drawn to the non affected side
• Inability to wrinkle forehead (peripheral lesion)
• May be associated with ear pain, impaired taste sensation on the anterior two-thirds of the tongue, decreased tearing, and hyperacusis

Diagnostic Tests

Electrodiagnostic studies help determine the prognosis, and imaging studies can define potential surgical causes of facial palsy.

These tests are not necessary in all patients.

Patients with a typical lesion that is incomplete and recovers do not need further study.

Electrodiagnostic studies (EMG, or motor nerve conduction study) and Imaging (CT, or MRI) are warranted if the physical signs are atypical, there is slow progression beyond three weeks, or if there is no improvement at six months.

Screening blood studies for underlying systemic disease or infection should also be considered in these cases.

No test provides prognostic information sufficiently early as to be used for determining who should or should not be treated

Risk Stratification and Prognosis

The House-Brackmann grading system was devised both as a clinical indicator of severity and also an objective record of progress.

Clinically incomplete lesions tend to recover.

The natural history without treatment was described in a study of 1011 patients in 1982:

-67% had incomplete paralysis, with 94% rate of return to normal function -33% had complete paralysis, with 60% rate of return to normal function -By 3 weeks, 71% had complete recovery, 13% had slight sequelae , and 16% had residual weakness

Herpes zoster is associated with more severe paresis and worse prognosis compared with "idiopathic" Bell's palsy.

There is a favorable prognosis if some recovery is seen within the first 21 days of onset.

In severe lesions that recover, the outgrowth of new axons from the injury site may be disorganized and misdirected.

On blinking there is twitching of the angle of the mouth, and on smiling the eye may close or wink.

With misdirected autonomic fibers, a salivary stimulus may result in excess lacrimation, the syndrome of "crocodile tears."

Recurrent attacks of on either the ipsilateral or contralateral side have been observed in 7 to 15% of patients.

Treatment

Eye care

In severe cases, the cornea may be at risk because of poor eyelid closure and reduced tearing, which may result in drying and abrasion.

Risk for blindness due to corneal trauma is significant, especially if there is 5th nerve concomitant damage.

Artificial tears, every hour while awake, and ophthalmic ointments at night.

Protective glasses or goggles

Patches can be used at night, but tape should not be placed directly on the eyelid since the patch could slip and abrade the cornea.

Rarely tarsorrhaphy or temporary implantation of a gold weight into the upper lid.

Glucocorticoid and Antiviral Therapy

The mainstay of pharmacologic therapy is early short-term oral glucocorticoid treatment

It is established as effective by randomized controlled trials: Prednisone 1mg/kg up to 60mg PO daily for 10 days

The suspicion that Bell's palsy is caused by herpes simplex virus in most patients led to trials of antiviral therapy

Compared with placebo, these trials found no benefit for antiviral therapy alone.

Data is conflicting with regard to the possibility of additional benefit when antiviral agents are administered with glucocorticoids.

In a meta-analysis involving 18 trials and 2786 patients, treatment with glucocorticoids alone was associated with a reduced risk of unfavorable recovery (relative risk [RR] 0.69, 95% CI 0.55-0.87), whereas treatment with antiviral agents alone was not (RR 1.14, 95% CI 0.80-1.62).

In pooled data from eight trials, the same meta-analysis found a trend towards a reduced risk of unfavorable recovery for combined antiviral and glucocorticoid treatment compared with glucocorticoid treatment alone, but the outcome just missed statistical significance (RR 0.75, 95% CI 0.56-1.0).

In a second meta-analysis of six trials and 1145 patients, there was no significant benefit of combined antiviral and glucocorticoid treatment for achieving at least partial facial muscle recovery (odds ratio 1.5, 95% CI 0.83-2.69).

Neither excludes the possibility of marginal benefit when antiviral therapy is combined with glucocorticoids.

Acyclovir 2000-4000 mg/24 h PO divided 5 times a day for 7-10 d

Valcyclovir 1000-3000 mg/24 h PO for 5 d

Bell’s Palsy-induced Blepharospasm

Blepharospasm associated with Bell's palsy has been rarely reported so far

Seven patients previously reported: all women.

In five of the seven patients, blepharospasm appeared within a month after the onset of Bell’s palsy.

The majority of patients with blepharospasm have a high incidence of local ocular symptoms prior to or at the onset of blepharospasm, such as blepharitis, conjunctivitis, dry eyes or photophobia.

Chronically disturbed sensory inputs to the central nervous system due to lagophthalmos and corneal irritation may contribute to the generation of blepharospasm.

In patients with Bell’s palsy, there is an enhanced blink reflex secondary to inputs from the paralyzed side compared which those of the non-paralyzed side.

Abnormal afferent input from the paralyzed side contributes to the abnormal sensitization of the blink reflex, thus facilitating the induction of abnormal facial motor outputs such as blepharospasm.

It is unclear why Bell’s palsy-induced blepharospasm is extremely rare.

Additional Resources

• Sullivan FM, Swan IRC, Donnan PT, et al. Early treatment with prednisolone or acyclovir in Bell's palsy. N Engl J Med 2007;357:1598-1607.
• "The Merck Manual"
• New England Journal of Medicine, Sept. 2004
• Lambert, Michael. (2007-03-05) "Bell's Palsy." (Website.) Emedicine. Retrieved on 2007-09-27.

External links

• managment and treatment of facial paralysis
• Bell's Palsy Information Site, has a FAQ
• Bell's Palsy and Pregnancy
• Bell's Palsy Patient Info - Neurology Channel
• Living with Facial Palsy, a site for parents of children with Facial Palsy
• Links to pictures of Bells palsy (Hardin MD/Univ of Iowa)
• Bell's Palsy Association