Hemifacial Spasm
Key Points
Hemifacial spasm is a movement disorder characterized by spasms of the muscles innervated by the facial nerve
It typically begins in the fifth to sixth decades of life
The most common cause for hemifacial spasm is an ectatic blood vessel that compresses the facial nerve at the root exit zone in the pons
The most common offending vessels are the anterior inferior cerebellar artery, posterior inferior cerebellar artery, and the vertebrobasilar artery and vein
Hemifacial spasms begin clinically as unilateral facial muscle fasciculations, which later become more pronounced contractions of the orbicularis oculi muscle and progressively spread to other facial muscles
Several drugs have been reported to show some efficacy in the management of hemifacial spasm including carbamazepine, clonazepam, gabapentin, baclofen, and haloperidol
Peripheral chemodenervation with botulinum toxin is the treatment of choice for most patients with hemifacial spasm
Without treatment, hemifacial spasm can interfere with talking and eating and in rare cases lead to functional blindness
With botulinum toxin injections, more than 80% of patients can experience significant relief of spasms for 12 to 16 weeks
Hemifacial spasm (HFS) is a movement disorder characterized by spasms of the muscles innervated by the facial nerve (CN 7). The major clinical manifestation is involuntary unilateral clonic and/or tonic contractions of the muscles of facial expression. Symptoms often begin in the periorbital muscles but later progress to involve muscles of the mid-and lower face and platysma. In severe cases, eyelid closure may result in functional blindness.
The condition was first described by Schultze in 1875, in a 56-year-old man with involuntary movements involving the left side of his face.1 On postmortem examination, a giant aneurysm of the left vertebral artery was found compressing the left facial nerve. In 1886, Gowers expanded the definition and described the classical features of this condition.2 Several years later, Édouard Brissaud presented a similar case in a 35-year-old female with clonic contractions of the muscles of the right half of her face that became worse at times of stress.3 The name of this condition was introduced by Babinski in 1905 as hémispasme facial,4 and he also reported that, when the orbicularis oculi muscle contracts, the frontalis muscle also contracts, raising the eyebrow, distinguishing HFS from blepharospasm (see Chapter 32).
The prevalence of HFS in the United States has been reported at 11 per 100,000 population, with a 2:1 female preponderance (14.5 per 100,000 in females and 7.4 per 100,000 in males).5 Another study from Norway gave a similar prevalence of 9.8 per 100,000.6 Few epidemiologic data are available, but HFS has been reported to be more common in some Asian populations than in Caucasians.7
Primary HFS typically begins in the fifth to sixth decades of life. Fewer than 6% of patients present before the age of 30 years,8 and presentation before the age of 40 years should elicit a search for an underlying secondary cause. HFS is usually sporadic, but occasional familial cases have been described, with a maximum incidence of 2% to 3% in several large series.9,10 There is a definite female predominance with reported ratios of 1.8:1,11,12,13 to as much as 3:1.14
Bilateral cases have been reported, but are very rare, occurring in an estimated 0.6% to 5% of HFS patients.11,15,16 In these cases the disease usually starts unilaterally and, only after several months to years, involves the contralateral side. Unlike essential blepharospasm, muscle contractions in bilateral HFS are asymmetrical, with the spasm on each side completely independent. One case of presumed symmetrical bilateral HFS has been described, attributed to supposed anatomic connections between the bilateral facial nuclei.17
Etiology and Pathophysiology
The root exit or entry zone of a nerve is the junction between the central and the peripheral segments of a cranial nerve. In this zone, there is a transition from the central oligodendroglial cells to peripheral Schwann cells that are responsible for myelination of the nerve. The cranial nerves in this zone also lack an epineurium and are covered only by an arachnoid membrane. Because of this anatomic structure, in this zone the nerve fiber is more susceptible to mechanical injury.18
The most common cause for HFS is an ectatic blood vessel that compresses the facial nerve at this root exit zone.19 In their review of 22 published reports, Miller and Miller20 found the most common offending vessels to be the anterior inferior cerebellar artery (37%), the posterior inferior cerebellar artery (30%), and the vertebrobasilar artery and
veins (23%). Chronic compression by these vessels causes mechanical injury to the vulnerable nerve segment at the exit zone, resulting in local demyelination.21 It has been proposed that this allows ephaptic transmission of impulses, or local exchange of electric fields, between neighboring neurons across these demyelinated segments, leading to excessive or abnormal firing.9
veins (23%). Chronic compression by these vessels causes mechanical injury to the vulnerable nerve segment at the exit zone, resulting in local demyelination.21 It has been proposed that this allows ephaptic transmission of impulses, or local exchange of electric fields, between neighboring neurons across these demyelinated segments, leading to excessive or abnormal firing.9
HFS can be either primary or secondary. Primary HFS results from compression of the seventh nerve at the root exit zone in the posterior cranial fossa by an aberrant or ectatic vessel. Secondary HFS can be caused by a wide variety of etiologies including cerebellopontine angle tumors, arteriovenous malformations, arterial aneurysms, cerebellopontine arachnoid cysts, stroke, trauma, demyelinating disorders, infections such as otitis media, tubercular meningitis, structural abnormalities of the posterior cranial fossa, and Bell palsy.13 The incidence of posterior fossa tumors causing HFS is about 0.4%,22 so that patients with new-onset HFS should be imaged before treatment.
 FIGURE 35.1 A-D, Clinical features of hemifacial spasm. |
Clinical Presentation
Primary HFS usually begins with unilateral facial muscle fasciculations, followed later by more pronounced contractions of the orbicularis oculi muscle (Figure 35.1). In 80% to 90% of cases, the spasms are initially limited to the periocular
region but progressively spread thereafter to other facial nerve branches.23,24,25
region but progressively spread thereafter to other facial nerve branches.23,24,25
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