(See also Overview of Neuro-ophthalmologic and Cranial Nerve Disorders Overview of Neuro-ophthalmologic and Cranial Nerve Disorders Dysfunction of certain cranial nerves may affect the eye, pupil, optic nerve, or extraocular muscles and their nerves; thus, they can be considered cranial nerve disorders, neuro-ophthalmologic... read more .)
Historically, Bell palsy was thought to be idiopathic facial nerve (peripheral 7th cranial nerve) palsy. However, facial nerve palsy is now considered a clinical syndrome with its own differential diagnosis, and the term "Bell palsy" is not always considered synonymous with idiopathic facial nerve palsy. About half the cases of facial nerve palsy are idiopathic.
The mechanism for what was previously thought to be idiopathic facial nerve palsy is presumably swelling of the facial nerve due to an immune or viral disorder. Current evidence suggests that common viral causes are
Other viral causes include coxsackievirus, cytomegalovirus Cytomegalovirus (CMV) Infection Cytomegalovirus (CMV, human herpesvirus type 5) can cause infections that have a wide range of severity. A syndrome of infectious mononucleosis that lacks severe pharyngitis is common. Severe... read more , adenovirus Adenovirus Infections Infection with one of the many adenoviruses may be asymptomatic or result in specific syndromes, including mild respiratory infections, keratoconjunctivitis, gastroenteritis, cystitis, and primary... read more , and the Epstein-Barr Infectious Mononucleosis Infectious mononucleosis is caused by Epstein-Barr virus (EBV, human herpesvirus type 4) and is characterized by fatigue, fever, pharyngitis, and lymphadenopathy. Fatigue may persist weeks or... read more , mumps Mumps Mumps is an acute, contagious, systemic viral disease, usually causing painful enlargement of the salivary glands, most commonly the parotids. Complications may include orchitis, meningoencephalitis... read more , rubella Rubella (See also Congenital Rubella.) Rubella is a contagious viral infection that may cause adenopathy, rash, and sometimes constitutional symptoms, which are usually mild and brief. Infection during... read more , and influenza Influenza Influenza is a viral respiratory infection causing fever, coryza, cough, headache, and malaise. Mortality is possible during seasonal epidemics, particularly among high-risk patients (eg, those... read more B viruses. The swollen nerve is maximally compressed as it passes through the labyrinthine portion of the facial canal, resulting in ischemia and paresis.
Various other disorders (eg, diabetes Diabetes Mellitus (DM) Diabetes mellitus is impaired insulin secretion and variable degrees of peripheral insulin resistance leading to hyperglycemia. Early symptoms are related to hyperglycemia and include polydipsia... read more , Lyme disease Lyme Disease Lyme disease is a tick-transmitted infection caused by the spirochete Borrelia species. Early symptoms include an erythema migrans rash, which may be followed weeks to months later by neurologic... read more , sarcoidosis Sarcoidosis Sarcoidosis is an inflammatory disorder resulting in noncaseating granulomas in one or more organs and tissues; etiology is unknown. The lungs and lymphatic system are most often affected, but... read more ) can cause facial nerve palsy.
The facial muscles are innervated peripherally (infranuclear innervation) by the ipsilateral 7th cranial nerve and centrally (supranuclear innervation) by the contralateral cerebral cortex. Central innervation tends to be bilateral for the upper face (eg, forehead muscles) and unilateral for the lower face. As a result, both central and peripheral lesions tend to paralyze the lower face. However, peripheral lesions (facial nerve palsy) tend to affect the upper face more than central lesions (eg, stroke) do.
Pain behind the ear often precedes facial paresis in idiopathic facial nerve palsy. Paresis, often with complete paralysis, develops within hours and is usually maximal within 48 to 72 hours.
Patients may report a numb or heavy feeling in the face. The affected side becomes flat and expressionless; the ability to wrinkle the forehead, blink, and grimace is limited or absent. In severe cases, the palpebral fissure widens and the eye does not close, often irritating the conjunctiva and drying the cornea.
Sensory examination is normal, but the external auditory canal and a small patch behind the ear (over the mastoid) may be painful to the touch. If the nerve lesion is proximal to the geniculate ganglion, salivation, taste, and lacrimation may be impaired, and hyperacusis may be present.
Facial nerve palsy is diagnosed based on clinical evaluation. There are no specific diagnostic tests.
Facial nerve palsy can be distinguished from a central facial nerve lesion (eg, due to hemispheric stroke or tumor), which causes weakness primarily of the lower face, sparing the forehead muscle and allowing patients to wrinkle their forehead; also, patients with central lesions can usually furrow their brow and close their eyes tightly.
Usually, clinicians can also distinguish idiopathic facial nerve palsy from other disorders that cause peripheral facial nerve palsies based on their characteristic symptoms and signs; these disorders include the following:
Middle ear infections Otitis Media (Acute) Acute otitis media is a bacterial or viral infection of the middle ear, usually accompanying an upper respiratory infection. Symptoms include otalgia, often with systemic symptoms (eg, fever... read more or mastoid infections Mastoiditis Mastoiditis is a bacterial infection of the mastoid air cells, which typically occurs after acute otitis media. Symptoms include redness, tenderness, swelling, and fluctuation over the mastoid... read more
Petrous bone fractures
Carcinomatous or leukemic nerve invasion
Cerebellopontine angle or glomus jugulare tumors
Also, the other disorders that cause peripheral facial nerve palsy typically develop more slowly than idiopathic facial nerve palsy. Thus, if patients have any other neurologic symptoms or signs or if symptoms developed gradually, MRI should be done.
In idiopathic facial nerve palsy, MRI may show contrast enhancement of the facial nerve at or near the geniculate ganglion or along the entire course of the nerve. However, its enhancement may reflect other causes, such as meningeal tumor. If the paralysis progresses over weeks to months, the likelihood of a tumor (eg, most commonly schwannoma) compressing the facial nerve increases. MRI can also help exclude other structural disorders causing facial nerve palsy. CT, usually negative in Bell palsy, is done if a fracture is suspected or if MRI is not immediately available and stroke is possible.
In addition, acute and convalescent serologic tests for Lyme disease are done if patients have been in a geographic area where ticks and Lyme disease are endemic.
For all patients, a chest x-ray is taken or CT is done and serum ACE is measured to check for sarcoidosis. Serum glucose is measured to check for diabetes. Viral titers are not helpful.
In idiopathic facial nerve palsy, the extent of nerve damage determines outcome. If some function remains, full recovery typically occurs within several months. Nerve conduction studies and electromyography are done to help predict outcome. The likelihood of complete recovery after total paralysis is 90% if nerve branches in the face retain normal excitability to supramaximal electrical stimulation and is only about 20% if electrical excitability is absent.
Regrowth of nerve fibers may be misdirected, innervating lower facial muscles with periocular fibers and vice versa. The result is contraction of unexpected muscles during voluntary facial movements (synkinesia) or crocodile tears during salivation. Chronic disuse of the facial muscles may lead to contractures.
Corneal drying must be prevented by frequent use of natural tears, isotonic saline, or methylcellulose drops and by intermittent use of tape or a patch to help close the eye, particularly during sleep. Tarsorrhaphy is occasionally required.
In idiopathic facial nerve palsy, corticosteroids, if begun within 48 hours after onset, result in faster and more complete recovery (1 Treatment reference Facial nerve (7th cranial nerve) palsy is often idiopathic (formerly called Bell palsy). Idiopathic facial nerve palsy is sudden, unilateral peripheral facial nerve palsy. Symptoms of facial... read more ). Prednisone 60 to 80 mg orally once a day is given for 1 week, then decreased gradually over the 2nd week.
Antiviral drugs effective against herpes simplex virus (eg, valacyclovir 1 g orally 3 times a day for 7 to 10 days, famciclovir 500 mg orally 3 times a day for 5 to 10 days, acyclovir 400 mg orally 5 times a day for 10 days) have been prescribed, but recent data suggest that antiviral drugs provide no benefit (1 Treatment reference Facial nerve (7th cranial nerve) palsy is often idiopathic (formerly called Bell palsy). Idiopathic facial nerve palsy is sudden, unilateral peripheral facial nerve palsy. Symptoms of facial... read more ).
In facial nerve palsy, patients cannot move the upper and lower part of their face on one side; in contrast, central facial nerve lesions (eg, due to stroke) affect primarily the lower face.
Evidence that the mechanism for what was previously thought to be idiopathic facial nerve palsy is increasingly implicating herpes viruses.
Diagnosis is clinical, but if onset is not clearly acute, MRI should be done.
If given early, corticosteroids are helpful for idiopathic facial nerve palsy; antivirals probably provide no benefit.