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Inactivated intranasal influenza vaccine that was introduced and since withdrawn from the market in Switzerland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

Onset over hours (maximal symptoms by 48 hours)

• Eyebrow sag with inability to close eye
• Nasolabial fold flattening with mouth drawn to affected side
• Inability to wrinkle forehead (peripheral lesion)
• May be associated with or preceded by ear pain (~20%)
• May be associated with:

1. Impaired taste 23%
2. Increased lacrimation 24%
3. Hyperacusis 7%

Diagnosis

Bell's palsy is a diagnosis of exclusion; in many cases, no specific cause can be ascertained.

Testing for Lyme not indicated unless other suggestive symptoms or risk factors.

Other Imaging Findings

Imaging only if atypical symptoms or slow progression (risk of tumor). Electromyography (EMG) may help with prognosis in patients with complete cranial nerve (CN) VII paralysis

Investigation

Clinicians should determine whether all branches of the facial nerve are involved, or whether the forehead muscles are spared. Since these receive innervation from both sides of the brain, the forehead can still be wrinkled by a patient whose facial palsy is caused by a problem in the brain rather than in the facial nerve itself.

Facial palsy results from inability to control movement in the facial muscles. The facial muscles become weak or paralyzed. There is no specific treatment for Bell's palsy, and it typically subsides on its own within 2-3 weeks.

Risk Stratification and Prognosis

Excellent or complete recovery in 80% within weeks-months. Recovery depends on initial severity

• Incomplete lesions: 94% recover to normal function
• Complete lesions: 60% recover to normal function

Treatment

Eye care: nocturnal patch, lacrilube, artificial tears if poor lid closure

Pharmacotherapy

Glucocorticoids: +/- higher rate of recovery if reaction at onset
Antivirals: ACV 400 mg 5xd + prednisone better than prednisone alone
Valacyclovir: 1 g tid x 7d = easier alternative to ACV

Treatment is a matter of controversy. In patients presenting with incomplete facial palsy, treatment may be unnecessary. However, patients presenting with complete paralysis, marked by an inability to close the eyes and mouth on the involved side, are usually treated with anti-inflammatory corticosteroids. Prednisolone, a corticosteroid, if used early in treatment of Bell's palsy, significantly improves the chances of complete recovery at 3 and 9 months when compared to treatment with acyclovir, an anti-viral drug, or no treatment at all. The likely association of Bell's palsy with the herpes virus has led most American neurologists to prescribe a course of anti-viral medication (such as acyclovir) to all patients with unexplained facial palsy.

People who think they may have Bell's Palsy should consult their doctor as soon as possible. Many times, the medications will not be effective if administered too late after the onset.

Although most patients (60–80%) recover completely from Bell's palsy within several weeks, some require several months, and others may be left with deficits of varying degrees.

Complications

Major complications of the condition are chronic loss of taste (ageusia), chronic facial spasm and corneal infections. To prevent the latter, the eyes may be protected by covers, or taped shut during sleep and for rest periods, and tear-like eye drops or eye ointments may be recommended, especially for cases with complete paralysis. Where the eye does not close completely, the reflex is also affected; great care should be taken to protect the eye from injury.

Another complication can occur in case of incomplete or erroneous regeneration of the damaged facial nerve. The nerve can be thought of as a bundle of smaller individual nerve connections which branch out to their proper destinations. During regrowth, nerves are generally able to track the original path to the right destination - but some nerves may sidetrack leading to a condition known as synkinesis. For instance, regrowth of nerves controlling muscles attached to the eye may sidetrack and also regrow connections reaching the muscles of the mouth. In this way, movement of one also affects the other. For example, when the person closes the eye, the corner of the mouth will lift, or when smiling, the eye will close (synkinesis).

In addition, around 6% of patients exhibit crocodile tear syndrome on recovery, where they will shed tears while eating. This is thought to be due to faulty regeneration of the facial nerve, a branch of which controls the lacrimal and salivary glands.

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