Bell's palsy
| Bell's palsy | |
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| 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- Inactivated intranasal influenza vaccine that was introduced and since withdrawn from the market in Switzerland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.
- Related to the severity of the lesion.
- 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 associated with more severe paresis and worse prognosis compared with "idiopathic" Bell's palsy.
- Favorable prognosis if some recovery 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."
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
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.
References
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
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