Disorders of Overactivity of the Seventh Cranial Nerve
Disorders of CN VII, its nucleus, or the pyramidal or extrapyramidal pathways may produce hyperexcitable states. Benign essential blepharospasm (BEB), hemifacial spasm, and facial myokymia are the 3 most common disorders of overactivity (Table 11-4).
Benign essential blepharospasm
BEB is a bilateral condition that consists of episodic contraction of the orbicularis oculi. Onset usually occurs between the ages of 40 and 60 years. Initially, the spasms are mild and infrequent, but they may progress to the point that the patient’s daily activities are severely disrupted. In advanced cases, the patient’s eyelids cannot be pried open during an episode of spasm. Facial grimacing and other movements may be associated with the blepharospasm (Meige syndrome, Fig 11-10), and cogwheeling in the neck and extremities or other extrapyramidal signs may be noted. Tardive dyskinesia secondary to neuroleptic and antipsychotic drugs can produce spasms that involve the mouth. Extrapyramidal disorders such as parkinsonism, Huntington disease, and basal ganglia infarction may be accompanied by some degree of blepharospasm.
Although the exact cause of BEB is unknown, increasing evidence acquired through functional neuroimaging suggests that it is caused by basal ganglia dysfunction. The clinician evaluating a patient with blepharospasm should exclude causes of reflex blepharospasm, in particular severe dry eye, intraocular inflammation, and meningeal irritation (usually associated with photophobia). Stress may exacerbate the condition. Neuroradiologic studies are generally unrevealing and rarely indicated.
The efficacy of medical therapy for BEB is generally limited. Tinted lenses, such as those with an FL-41 tint, may improve blink frequency and light sensitivity. The treatment of choice is injection of botulinum toxin (onabotulinumtoxinA, incobotulinumtoxinA, abobotulinumtoxinA, or rimabotulinumtoxinB) into the orbicularis oculi muscle. Because the effect of the toxin is temporary, lasting only a few months, repeat injections are necessary. The efficacy of the drug relates to its ability to cause muscle weakness. Complications such as ptosis, local ecchymosis, ectropion, diplopia, lagophthalmos, and exposure keratopathy are usually mild and transient. Treatment typically consists of 4–8 injection sites per periorbita. The central portion of the pretarsal orbicularis oculi muscle should be avoided to minimize the chance of inducing ptosis.
Table 11-4 Comparison of the Common Causes of CN VII Overactivity
Figure 11-10 Benign essential blepharospasm with Meige syndrome. This patient has contraction of the orbicularis oculi muscles in association with facial grimacing.
(Courtesy of Eric Eggenberger, DO.)
Treatment with surgical myectomy is reserved for patients who are refractory to botulinum toxin injection. Treatment failure can be seen in patients with pure blepharospasm but is more commonly seen in patients with blepharospasm associated with apraxia of eyelid opening. See BCSC Section 7, Oculofacial Plastic and Orbital Surgery, for a more extensive discussion on surgical myectomy.
BEB may cause psychological distress, with some patients withdrawing socially as the symptoms worsen. Thus, counseling may be as valuable as the medical and surgical management of this condition. The Benign Essential Blepharospasm Research Foundation (www.blepharospasm.org) aids research efforts and provides education and support to blepharospasm patients.
Ross AH, Elston JS, Marion MH, Malhotra R. Review and update of involuntary facial movement disorders presenting in the ophthalmological setting. Surv Ophthalmol. 2011; 56(1):54–67.
Hemifacial spasm is characterized by unilateral episodic spasms that involve the facial musculature and typically last from a few seconds to minutes. The disorder frequently begins as intermittent twitching of the orbicularis oculi muscle but, over the course of several years, spreads to involve all the facial muscles on 1 side (Fig 11-11). Episodes may increase in frequency for weeks to months and then abate for months at a time. CN VII function is usually intact, although, over time, subtle ipsilateral facial weakness may develop. Unlike BEB, the spasms can occur during sleep.
The pathogenesis of hemifacial spasm is most commonly compression of the CN VII root exit zone by a dolichoectatic vessel. Abnormal firing in the motor nucleus or ephaptic transmission of nerve impulses causes innervation directed toward a particular muscle group to excite adjacent nerve fibers that are directed to another muscle group. Less commonly, tumors within the cerebellopontine angle, Bell palsy, previous injury to CN VII, or demyelination may lead to the spasms; therefore, MRI and magnetic resonance angiography (MRA) of the brain is typically performed to exclude a compressive lesion or other secondary causes.
Figure 11-11 Hemifacial spasm. This 73-year-old woman has intermittent twitching involving the entire right side of the face.
(Courtesy of Rod Foroozan, MD.)
Botulinum toxin injection into the periocular and facial muscles has proved very effective and is the treatment of choice for hemifacial spasm in most patients. Reinjection is required, at typical intervals of 3–4 months. Hemifacial spasm responds to lower doses of botulinum toxin than does blepharospasm.
Carbamazepine, clonazepam, or baclofen may provide improvement in some patients. Suboccipital craniectomy with placement of a sponge between CN VII and the offending blood vessel (microvascular decompression) may be considered for advanced cases or younger patients. Surgical decompression may offer a cure but carries higher risks than alternative treatments.
Yaltho TC, Jankovic J. The many faces of hemifacial spasm: differential diagnosis of unilateral facial spasms. Mov Disord. 2011;26(9):1582–1592.
Spastic paretic facial contracture
Spastic paretic facial contracture is a rare disorder characterized by unilateral facial contracture with associated facial weakness. Typically, it begins with myokymia of the orbicularis oculi muscle, which gradually spreads to most of the ipsilateral facial muscles. At the same time, tonic contracture of the affected muscles becomes evident. Over weeks to months, ipsilateral facial weakness develops, and voluntary facial movements of the affected side diminish. Spastic paretic facial contracture is a sign of pontine dysfunction in the region of the CN VII nucleus, often caused by a pontine neoplasm. Damage to the nucleus causes facial weakness, and involvement of supranuclear connections leads to facial spasticity.
Facial myokymia is characterized by continuous unilateral fibrillary or undulating contraction of facial muscle bundles. Occasionally, these rippling movements begin within a portion of the orbicularis oculi and may spread to involve most of the facial muscles.
Facial myokymia typically signifies intramedullary disease of the pons involving the CN VII nucleus or fascicle. It is usually the result of a pontine glioma in children and multiple sclerosis in adults. In rare instances, myokymia occurs in patients with Guillain-Barré syndrome. Myokymia may be relieved with carbamazepine, phenytoin, or injection of botulinum toxin.
Intermittent fluttering of the orbicularis oculi (benign eyelid myokymia) is relatively common. The phenomenon usually lasts for days or weeks. In rare cases, eyelid myokymia can last for months; these patients may benefit from an injection of botulinum toxin. Caffeine, stress, and sleep deprivation are common contributing factors.
Banik R, Miller NR. Chronic myokymia limited to the eyelid is a benign condition. J Neuro-ophthalmol. 2004;24(4):290–292.
In rare instances, focal cortical seizures are manifested by gross clonic movements involving only 1 side of the face. The eyes deviate away from the side of the seizure focus during the episode; the patient’s ipsilateral hand may also have clonic movements. Frequently, Todd paralysis, a transient supranuclear facial paresis, follows the seizure, and the eyes may deviate toward the side of the prior seizure focus.
Oral facial dyskinesias (eg, tardive dyskinesia) are usually observed after long-term use of major tranquilizers and may persist even after the drugs are stopped. Habit spasm such as facial tic or nervous twitch is relatively common, particularly in childhood, and is characterized by involuntary, repetitive, reproducible facial movements that can be promptly inhibited on command. These movements tend to disappear in time without treatment. Only in rare cases does Tourette syndrome present with facial twitching alone.
Jung HY, Chung SJ, Hwang JM. Tic disorders in children with frequent blinking. J AAPOS. 2004;8(2):171–174.
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.