First described by Gowers in 1884, hemifacial spasm represents a segmental myoclonus of muscles innervated by the facial nerve. Hemifacial spasm presents in the fifth or sixth decade of life, almost always unilaterally, although bilateral involvement may occur rarely in severe cases. Hemifacial spasm generally begins with brief clonic movements of the orbicularis oculi and spreads over years to other facial muscles (corrugator, frontalis, orbicularis oris, platysma, zygomaticus).[1, 2]
Clonic movements progress to sustained tonic contractions of involved musculature. Chronic irritation of the facial nerve or nucleus, the near-universal cause of hemifacial spasm, may arise from numerous underlying conditions.
Facial musculature is subject to the same movement disorders as muscles of the limbs or trunk. Myoclonus, dystonia, and other movement disorders present with specific syndromes in the facial musculature. An understanding of the underlying mechanism leads to appropriate diagnostic evaluation and potential treatment.
The causes of hemifacial spasm include vascular compression, facial nerve compression by a mass, brainstem lesions such as stroke or multiple sclerosis plaques, and secondary causes such as trauma or Bell's palsy.[3]
Although specific treatments are available for many craniofacial movement disorders, botulinum toxin (BTX) chemodenervation has proven useful in many of these disorders, supplanting surgery and medical therapy.
For patient education information, see the Procedures Center, as well as BOTOX® Injections.
Irritation of the facial nerve nucleus is believed to lead to hyperexcitability of the facial nerve nucleus, while irritation of the proximal nerve segment may cause ephaptic transmission within the facial nerve. Either mechanism explains the rhythmic involuntary myoclonic contractions observed in hemifacial spasm.[4]
Compressive lesions (eg, tumor, arteriovenous malformation, Paget disease) and noncompressive lesions (eg, stroke, multiple sclerosis plaque, basilar meningitis) may present as hemifacial spasm. Most instances of hemifacial spasm previously thought to be idiopathic were probably caused by aberrant blood vessels (eg, distal branches of the anterior inferior cerebellar artery or vertebral artery) compressing the facial nerve within the cerebellopontine angle.
Hemifacial spasm affects all races equally. There is a slight female preponderance. Idiopathic hemifacial spasm typically begins in the fifth or sixth decade of life. Onset of hemifacial spasm in patients younger than 40 years is unusual and often heralds an underlying neurologic illness (eg, multiple sclerosis).
Hemifacial spasm rarely remits spontaneously. Current treatments, fortunately, prove highly effective. Patients should be counseled, however, that treatments are likely to continue indefinitely.
Involuntary facial movement is the only symptom of hemifacial spasm. Fatigue, anxiety, or reading may precipitate the movements. Spontaneous hemifacial spasm manifests with facial spasms that represent myoclonic jerks and are analogous to segmental myoclonus, which may affect other body regions. Postparalytic hemifacial spasm, following facial nerve trauma such as Bell's palsy, manifests as facial synkinesis and contracture.
Physical findings are restricted to the involved facial muscles. The examiner will observe these contracting synkinetically (all at the same time), usually with an irregular frequency. Other neurological findings signal another process elsewhere, or an underlying process such as cerebrovascular disease or multiple sclerosis.
Prolonged contraction of the orbicularis oculus will result in temporary loss of vision in the involved eye, with impairment of activity.
Early cases of hemifacial spasm may be difficult to distinguish from facial myokymia, tics, or myoclonus originating in the cortex or brainstem. Neurophysiologic testing can be invaluable.
Spread and variable synkinesis on blink reflex testing and high-frequency discharges on electromyography (EMG) with appropriate clinical findings are diagnostic. Stimulation of one branch of the facial nerve may spread and elicit a response in a muscle supplied by a different branch. Synkinesis is not present in essential blepharospasm, dystonia, or seizures. Needle EMG shows irregular, brief, high-frequency bursts (150–400 Hz) of motor unit potentials, which correlate with clinically observed facial movements.
Magnetic resonance imaging is the imaging study of choice, especially if an underlying compressive lesion is suspected. Cerebral angiography offers little diagnostic value in hemifacial spasm. Ectatic blood vessels rarely are identified, and it is difficult to correlate vessels with the facial nerve. Perform angiography and/or magnetic resonance angiography prior to a vascular decompression surgical procedure. Angiography is often performed before decompressive surgery to clarify the vascular anatomy, because it may identify an aneurysm or vascular anomaly.[7]
In most patients with hemifacial spasm, the treatment of choice is injection of botulinum toxin under electromyographic (EMG) guidance. Chemodenervation safely and effectively treats most patients, especially those with sustained contractions. Relief of spasms occurs 3-5 days after injection and lasts approximately 6 months.
Medications used in the treatment of hemifacial spasm include carbamazepine and benzodiazepines for noncompressive lesions. Carbamazepine, benzodiazepines, and baclofen also may be used in patients who refuse botulinum toxin injections. Compressive lesions need to be treated surgically. Microvascular decompression surgery may be effective for those patients who do not respond to botulinum toxin. A study of 246 patients who underwent microvascular decompression surgery found no significant difference in outcomes and complications between patients who had botulinum toxin injections prior to their first surgery and those who did not.[8]
The treatment of choice for hemifacial spasm is botulinum toxin injection of botulinum toxin under EMG guidance. Side effects of botulinum toxin injection (eg, facial asymmetry, ptosis, facial weakness) usually are transient. Most patients report a highly satisfactory response. Caution patients that although botulinum toxin ablates the muscular spasm, the sensation of spasm often persists.[9, 10]
Medications may be used in early hemifacial spasm (when spasms are mild and infrequent) or in patients who decline botulinum toxin injection. Use medications in patients with noncompressive lesions and early idiopathic hemifacial spasm. Response to medication varies but can be satisfactory in early or mild cases. The most helpful agents are carbamazepine and benzodiazepines (eg, clonazepam). Often, medication effects attenuate over time, necessitating more aggressive treatment.
Treat compressive lesions surgically. Ectatic blood vessels cause hemifacial spasm by compressing the facial nerve as it exits the brainstem. Surgical decompression of these blood vessels can yield excellent results.[11, 12, 13, 14] A study evaluating the effect of microvascular decompression surgery on idiopathic hemifacial spasm with compression on different zones of facial nerve found that proper detection of offending vessels and complete decompression may increase cure rate.[15]
Patients with apparently idiopathic hemifacial spasm may benefit from posterior fossa exploration and microvascular decompression. Myectomy rarely is required.
The goal of pharmacotherapy is reduction of abnormal muscle contractions. Botulinum toxin type A is the treatment of choice.[16, 17] Carbamazepine, benzodiazepines, and baclofen may also be used in patients who refuse BTX injections or who are not surgical candidates.
Clinical Context: OnabotulinumtoxinA (BOTOX) is useful in reducing excessive, abnormal contractions associated with blepharospasm. It binds to receptor sites on the motor nerve terminals and, after uptake, inhibits the release of acetylcholine, blocking transmission of impulses in neuromuscular tissue. At 7-14 days after administration of the initial dose, assess patients for a satisfactory response. Increase the dose 2-fold over the previously administered dose in patients who experience incomplete paralysis of the target muscle.
Clinical Context: When botulinum toxin injection is indicated and type A toxin is ineffective, injection with type B toxin (rimabotulinumtoxinB [Myobloc]) should be considered.
Clinical Context: AbobotulinumtoxinA (Dysport) binds to receptor sites on the motor nerve terminals and, after uptake, inhibits release of acetylcholine, blocking transmission of impulses in neuromuscular tissue. At 7-14 days after administration of the initial dose, assess the patient for a satisfactory response. Increase the dose 2-fold over the previously administered dose in patients who experience incomplete paralysis of the target muscle.
Clinical Context: Xeomin, a botulinum toxin type A product, may be used if Botox proves unsuccessful, or is unavailable. It should produce satisfactory results, though systematic trials of Xeomin for HFS have not yet been reported. Excess administration will produce undesirable weakness and facial asymmetry.
Botulinum toxin type A is the drug of choice.[16, 17] It causes presynaptic paralysis of the myoneural junction and reduces abnormal contractions. Therapeutic effects may last 3-6 months.
Botulinum toxin type B is useful in reducing excessive, abnormal contractions associated with blepharospasm[18] ; binds to receptor sites on the motor nerve terminals and after uptake inhibits release of acetylcholine, blocking transmission of impulses in neuromuscular tissue; 7-14 d after administering initial dose, assess patients for a satisfactory response; increase doses 2-fold over previously administered dose for patients who experience incomplete paralysis of the target muscle.
Clinical Context: Clonazepam (Klonopin) is useful in suppressing muscle contractions by facilitating inhibitory GABA neurotransmission and other inhibitory transmitters.
Benzodiazepines may potentiate the effects of gamma-aminobutyric acid (GABA) and facilitate inhibitory GABA neurotransmission. It may act in the spinal cord to induce muscle relaxation. Treatment needs to be individualized for each patient.
Clinical Context: Baclofen (Lioresal) may induce hyperpolarization of afferent terminals and inhibit both monosynaptic and polysynaptic reflexes at the spinal level.
Muscle relaxants may inhibit the transmission of monosynaptic and polysynaptic reflexes at the spinal cord level.
Clinical Context: Carbamazepine (Tegretol) is effective in the treatment of hemifacial spasm and complex partial seizures. It appears to act by reducing polysynaptic responses and blocking posttetanic potentiation. Once a response is attained, attempt to reduce the dose to the minimum effective level or discontinue the drug at least once every 3 months. In patients who cannot tolerate carbamazepine, consider oxcarbazepine (dosage not yet established).
Clinical Context: Oxcarbazepine (Trileptal) is effective in partial complex epilepsy. It shows promise in hemifacial spasm. Oxcarbazepine may be considered when first-line agents (eg, botulinum toxin, carbamazepine) have failed or are contraindicated.
Anticonvulsants are used to manage severe muscle spasms and provide analgesia and mild sedation. Anticonvulsants are probably the best medications in terms of efficacy and long-term safety when botulinum toxin and surgery are not options.