CN VII innervates the facial muscles via the five branches of the motor root, the submandibular, sublingual, and lacrimal glands, and the taste organs on the anterior two-thirds of the tongue; and it provides sensation to the pinna of the ear. Facial palsies are either central or peripheral. Central lesions occur proximal to the CN VII nucleus in the pons. Lesions distal to the nucleus are classified as peripheral lesions. The ipsilateral frontalis muscle is functional or “spared” in central lesions since it receives innervation in the nucleus from both ipsilateral and contralateral motor cortices. Peripheral injuries involve the entire side of the face, including the forehead; thus, the forehead is not “spared.”
Most commonly, 7th-nerve dysfunction is idiopathic (Bell palsy). One percent of patients have bilateral involvement; 60% have a viral prodrome. There is no age, sex, or racial predilection. Patients note an acute onset over a few hours to days of facial weakness and may have numbness or pain on the ipsilateral face, ear, tongue, and neck, as well as a decrease or loss of ipsilateral tearing and saliva flow. Hearing is most commonly preserved.
Prognosis is variable. Facial weakness has a better prognosis for full recovery than complete paralysis. Palsies due to herpes zoster have a protracted course, and many do not fully resolve. In comparison, 80% of patients with Bell palsy completely recover within 3 months.
Management and Disposition
Initial examination should include a thorough examination of the ear (including sensorineural or conductive hearing loss), the eye (including lacrimation), and the CNs—especially extraocular muscles. Motor function of the 7th CN is evaluated by having the patient raise their eyebrows, smile, pucker, and frown. No single laboratory test is diagnostic but may be required for excluding other disorders. Screening CT or MRI of the head is of little value in the absence of additional findings on physical examination.
Antivirals combined with corticosteroids are associated with higher rates of motor recovery. Eye lubricants and taping the eye shut at night help prevent keratitis and ulceration. Referral to a neurologist should be made for follow-up care.
Facial nerve paralysis is a symptom, not a diagnosis.
If a provisional diagnosis of Bell palsy is made and no resolution of symptoms occurs, the diagnosis must be reconsidered. In patients misdiagnosed with Bell palsy, tumors are the most common missed etiology. MRI of the brainstem and internal auditory canal is indicated in these circumstances. Also consider Lyme disease in areas of high risk.
The finding of CN VI (lateral rectus) palsy along with CN VII palsy is suggestive of a brainstem stroke, which involves the ipsilateral CN VII as it partially surrounds the CN VI nucleus. Hence, always evaluate for CN VI palsy when evaluating CN VII palsy.
Further ED evaluation is required for facial palsy ...