Facial weakness or paralysis may occur with supranuclear, nuclear, or infranuclear lesions (Table 11-3).
Peripheral or lower motor neuron lesions that result in ipsilateral facial weakness may have numerous causes. Concomitant impairment of CN V, CN VI, or CN VIII or cerebellar signs may indicate cerebellar pontine angle tumors.
Bell palsy, which typically occurs in adults, represents the most common type of facial neuropathy, but it must remain a diagnosis of exclusion. Bell palsy is characterized by the sudden onset of facial paresis. Pain may either precede the palsy or occur concurrently. Patients with Bell Palsy may report facial numbness, although their cutaneous sensation is usually intact. These patients may also note decreased tearing, diminished taste, and dysacusis.
Although the etiology of Bell palsy is unknown, it is believed to be caused by autoimmune or viral-induced inflammatory or ischemic injury with swelling of the peripheral nerve. The incidence of Bell palsy is higher in pregnant women and in patients with diabetes mellitus or a family history of Bell palsy. If the facial weakness progresses over a period of more than 3 weeks, an alternative etiology should be considered (eg, a neoplastic process, inflammatory disorder such as sarcoidosis, or an infectious cause).
Approximately 85% of patients with Bell palsy experience a satisfactory recovery, although subtle signs of aberrant regeneration can be detected on examination. In these patients, recovery typically begins within 3 weeks of onset of the deficit and is complete by 2–3 months. In the remaining patients, recovery is incomplete, and significant synkinesis with co-contraction of a variety of facial muscles is common. Complete facial palsy at the time of presentation, impairment of lacrimation, dysacusis, pregnancy, diabetes mellitus, and advanced age are all poor prognostic factors.
Corticosteroids are commonly used to treat Bell palsy, and evidence from meta-analyses and randomized trials supports their efficacy. A 7–10-day course of oral corticosteroids is recommended for patients without systemic contraindications within the first 72 hours. The addition of an antiviral medication (eg, acyclovir, famciclovir, or valacyclovir) is of unclear benefit.
Neoplasms may involve CN VII in the cerebellopontine angle (eg, acoustic neuroma [Fig 11-9], meningioma), within the fallopian canal, or in the parotid gland. Such lesions may compress CN VII, resulting in facial synkinesis. Most of these lesions are best evaluated through magnetic resonance imaging (MRI) with intravenous contrast.
Various infectious agents can cause CN VII pathology. The nerve may be impaired from meningitis. Lyme disease, caused by the tick-borne spirochete Borrelia burgdorferi, can cause unilateral or bilateral facial palsies. Classic manifestations include a characteristic rash, arthritis, and meningopolyneuritis (see Chapter 14). The prognosis for CN VII palsy recovery following treatment of Lyme disease is excellent.
Figure 11-9 Facial nerve palsy. This 60-year-old patient experienced ocular irritation on the left side after excision of a left acoustic neuroma. A, The left eye will not close due to weakness of the left orbicularis oculi. B, Fortunately, corneal sensation remains intact, and the patient demonstrates an excellent Bell phenomenon.
(Courtesy of Steven A. Newman, MD.)
Herpes zoster that involves CN VII is called Ramsay Hunt syndrome. It is diagnosed through the identification of vesicles along the posterior aspect of the external auditory canal, over the tympanic membrane, or on the pinna. Pain is often severe, and postherpetic neuralgia may result. The prognosis for recovery is less promising than for Bell palsy. An isolated CN VII palsy, as well as other isolated or multiple CN palsies, may be the first sign of human immunodeficiency virus (HIV) seroconversion. Infectious disorders such as otitis media may spread to involve CN VII.
CN VII is the most common CN involved in sarcoidosis (see Chapter 14). The site of involvement is usually the parotid gland, which develops noncaseating granulomatous inflammation. CN VII involvement is frequently bilateral yet asymmetric.
Facial diplegia may occur in Guillain-Barré syndrome, especially in the variant Miller Fisher syndrome, when ophthalmoplegia and ataxia are also present. Cerebrospinal fluid analysis reveals an elevated protein level with a normal cell count, and deep tendon reflexes are usually absent. A high percentage of patients with Miller Fisher syndrome have anti-GQ1b IgG antibodies in their serum. Recovery is generally complete, and the serologic test results improve with clinical improvement.
CN VII palsy may occur from head trauma. The Battle sign (ecchymosis over the mastoid area) may be present and is associated with fractures of the temporal bone. Congenital facial palsy is frequently related to birth trauma from use of forceps and tends to resolve.
In Melkersson-Rosenthal syndrome, recurrent unilateral or bilateral facial paralysis is accompanied by chronic facial swelling and lingua plicata (furrowing of the tongue). The etiology of this disorder, which usually begins in childhood or adolescence, is unknown. The facial swelling is frequently marked and may be bilateral, even when facial paresis is only unilateral.
Given the extensive differential diagnosis for CN VII weakness, etiologic considerations in specific clinical situations deserve emphasis. Bilateral CN VII palsies are most frequently due to sarcoidosis, basilar meningitis (bacterial, viral, spirochetal), or Guillain-Barré syndrome. Recurrent unilateral CN VII involvement is most commonly idiopathic but may be caused by diabetes mellitus, Lyme disease, or Melkersson-Rosenthal syndrome. Progressive CN VII palsy is highly suggestive of a neoplastic etiology, either from tumor invasion (eg, brainstem, cerebellopontine, or parotid gland) or diffuse infiltration (eg, meningeal carcinomatosis). Further, accompanying CN palsies will aid in topographic localization of the lesion.
Schwartz SR, Jones SL, Getchius TS, Gronseth GS. Reconciling the clinical practice guidelines on Bell’s palsy from the AAO-HNSF and the AAN. Neurology. 2014;82(21):1927–1929.
Treatment options for seventh cranial nerve underactivity
In cases of orbicularis oculi involvement, treatment of corneal exposure may be necessary. Artificial tear preparations and lubricants are sufficient in mild cases. Taping the eyelid shut with lubricating ointment in the eye for sleep may be necessary. Moisture chambers have been used at night. Patients should be advised to avoid dusty and windy environments. Breakdown of corneal epithelium indicates the need for punctal plugs, tarsorrhaphy, or the injection of botulinum toxin to induce ptosis.
In patients with CN VII palsy, it is crucial to determine the status of CN V. Loss of corneal sensation combined with CN VII palsy is a particularly difficult clinical problem. The risk of combined neurotrophic and neuroparalytic keratitis warrants an aggressive approach, possibly including early tarsorrhaphy or an eyelid weight implant.
The simplest and most successful surgical treatment for corneal problems associated with chronic CN VII palsies is the implantation of gold or platinum eyelid weights, combined with horizontal eyelid tightening such as a lateral tarsal strip. To avoid the implantation of too small a weight, preoperative evaluation should include trials of various weights taped to the eyelid surface. The heaviest weight that can be lifted clear of the visual axis should be chosen. Later, if facial nerve function recovers, the weight can be removed.
Sohrab M, Abugo U, Grant M, Merbs S. Management of the eye in facial paralysis. Facial Plast Surg. 2015;31(2):140–144.
Excerpted from BCSC 2020-2021 series: Section 5 - Neuro-Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.