Cranial movement disorders: clinical features ... - Nature

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Cranial movement disorders: clinical features, pathophysiology, differential diagnosis and treatment Giovanni Fabbrini, Giovanni Defazio, Carlo Colosimo, Philip D Thompson and Alfredo Berardelli* INTRODUCTION

S U M M ARY Cranial movement disorders are a common neurological problem. These disorders can be limited to the cranial muscles alone or manifest as part of a more generalized movement disorder. Cranial movement disorders can originate from the highest (motor cortex) to the lowest (cranial nerve and muscle) levels of the motor system. Owing to the lack of diagnostic tests and biomarkers for these disorders, their differential diagnosis can be difficult even for the experienced neurologist. Advances have, however, been made in the identification and treatment of these conditions, and most can be managed effectively with appropriate knowledge of the diagnostic signs and effective treatments. Here, we review the clinical features, pathophysiologies and therapies of the main movement disorders that affect the face, jaw, tongue and palate. Keywords cranial dystonia, dyskinesias, hemifacial spasm, myoclonus, tics

Review criteria The papers for this review were retrieved through a PubMed search, with a predefined time interval of 1976–2008, using the following keywords: “blepharospasm”, “oromandibular dystonia”, “cranial dystonia”, “Meige’s syndrome”, “facial dyskinesias”, “L-dopa induced dyskinesias”, “tardive dyskinesias”, “tardive dystonia”, “tics”, “Tourette syndrome”, “facial myoclonus”, “facial myokymia”, “hemifacial spasm”, “facial synkinesias”, “facial myotonia”, “facial tremor”, “jaw tremor”, “lingual tremor”, “hemimasticatory spasm”, “stuttering”, “lingual dystonia”, “lingual myoclonus”, and “palatal tremor”. Only studies published in English were included.

G Fabbrini and C Colosimo run the Movement Disorders Clinic at the Department of Neurosciences and Neuromed Institute, “Sapienza” University of Rome, Rome, and G Defazio is Associate Professor of Neurology at the University of Bari, Bari, Italy. PD Thompson is full Professor of Neurology in the University Department of Medicine, Royal Adelaide Hospital, Adelaide, Australia and President-Elect of the Movement Disorders Society. A Berardelli is full Professor of Neurology in the Department of Neurological Sciences and Neuromed Institute, “Sapienza” University of Rome, Rome, Italy and Chairman of the European Section of the Movement Disorders Society. Correspondence *Department of Neurological Sciences and Neuromed Institute, “Sapienza” University of Rome, Viale dell’Università 30, 00185 Rome, Italy [email protected] Received 17 October 2008 Accepted 2 December 2008 www.nature.com/clinicalpractice doi:10.1038/ncpneuro1006

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Movement disorders that affect the face, jaw, tongue or palate are a frequent neurological problem. These disorders can be limited to the cranial muscles or manifest as part of a more generalized movement disorder. Cranial movement disorders can interfere with bulbar functions such as talking, chewing and swallowing. Some cranial hyperkinesias also cause intense social embarrassment. Epidemiological studies of facial movement disorders have concentrated mainly on cranial dystonia and hemifacial spasm, whereas most other cranial movement disorders are described mainly in clinical series or case reports. These differing types of data make precise evaluation of the prevalence of the different disorders within this group difficult. Furthermore, the variable clinical presentation of cranial movement disorders and the lack of diagnostic tests and biomarkers for these disorders make reaching a correct diagnosis a difficult clinical task even for movement disorder specialists. Cohesive information on these conditions is, therefore, required. To achieve a successful diagnosis, the diagnostic work-up should include the taking of a full family history, identification of possible exposure to drug treatment, and recognition of motor and nonmotor associated signs and symptoms, as well as a full physical examination. In this paper, we review the clinical features, pathophysiology, differential diagnosis and treatment of the main movement disorders that affect the face, jaw, tongue and palate. Movement disorders that affect the eyelids Blepharospasm

Blepharospasm is one of the most common forms of focal dystonia. The condition is characterized by intermittent, repetitive, involuntary contractions of the orbital and preseptal orbicularis oculi muscle fibers, which can result in narrowing of the palpebral fissure or complete closure of the eyelid. These spasms of eye closure always lead nature clinical practice neuroLOGY 93


Table 1 Cranial movement disorders that affect the eyelids. Disorder

Pattern

Activation profile

Associated features

Blepharospasm

Bilateral; stereotypic

Spontaneous, or induced by voluntary eyelid movements

Charcot sign; eye symptoms, geste antagoniste; dystonia (sometimes in other body parts also)

Apraxia of eyelid opening


Induced by voluntary eyelid opening

Frontalis contraction during eyelid closure; geste antagoniste

Apraxia of eyelid closure


Induced by voluntary eyelid closure

NA

Abbreviation: NA, not applicable.

to lowering of the eyebrow beneath the superior orbital rim, a condition called Charcot sign (Table 1, Figure 1).1–3 In addition, alternating dystonic discharges in the pretarsal orbicularis oculi muscles and levator palpebrae superioris muscles produce brief clonic flickering of the upper eyelids of both eyes.4 Characteristic features of blepharospasm include a high frequency of ocular symptoms before onset, and the patient’s performance of sensory tricks (‘geste antagoniste’) to ameliorate the dystonic movements associated with the condition—touching the eyebrow, in particular.5 Blepharospasm can occur in isolation, or with movements of the lower face and/or jaw (oromandibular dystonia). The combination of blepharospasm and oromandibular dystonia is called Meige syndrome. Blepharospasm usually starts between the fifth and seventh decades of life, and it affects more women than men. The prevalence of blepharo spasm is estimated to be between 12 and 133 cases per million individuals worldwide.6 In the majority of patients blepharospasm is primary in origin, resulting from genetic and/or environmental factors.7 Secondary causes of the disorder include Parkinson disease8 and progressive supra nuclear palsy.9 In patients with Parkinson disease, blepharospasm can be induced by deep brain stimulation of the subthalamic nucleus.10 Blepharospasm has been studied by several tech niques. In response to an electrical stimulus of the trigeminal nerve or to a sudden noise, patients exhibit increased excitability of the interneurons that mediate brainstem reflexes (blink reflex, masseter inhibitory reflex and auditory startle reaction).11,12 Transcranial magnetic stimulation studies reveal additional changes in cortical motor excitability and plasticity.13,14 Together, these findings suggest that reduced inhibition (or increased facilitation) occurs in patients with blepharospasm at the level of the brainstem 94 nature clinical practice neurOLOGY

and cortical motor areas.11 Sensory processing abnormalities are also evident in blepharo spasm, with alterations in spatial and temporal discrimination thresholds when somatosensory stimuli are applied to the face.15 Findings from neuroimaging studies support the general view that blepharospasm is associated with abnormalities in cortical and subcortical areas. Voxel-based morphometry of MRI scans has indicated that gray-matter volume is altered in the putamen,16 caudate nucleus and cerebellum in patients with blepharospasm.17 Conversely, however, another study found no cortical or subcortical changes on diffusion tensor imaging in patients with the condition.18 As in other forms of focal dystonia, striatal dopaminergic D2 receptor binding is reduced in blepharospasm.19 An increase in glucose metabolism on 2-[18F] fluoro-2-deoxyd-glucose (FDG)-PET has been found in the pons, cerebellum, thalamus and striatum in patients with the disorder.20 Finally, abnormal cortical sensorimotor processing has been demonstrated in patients with blepharospasm with use of H215O-PET and functional MRI.21,22 The differential diagnosis of blepharospasm includes apraxia of eyelid opening, hemifacial spasm and tics (Tables 1 and 2). Charcot sign occurs in blepharospasm but not in eyelidopening apraxia, so this symptom can help to differentiate these two disorders. Several clinical findings help to differentiate blepharospasm from hemifacial spasm. For instance, in blepharo spasm the muscle spasms are usually bilateral, whereas in hemifacial spasm the spasms almost invariably involve only one side of the face. In the rare cases of bilateral hemifacial spasm, contractions of the orbicularis oculi muscles are almost always independent and asynchronous, whereas in patients with blepharospasm contrac tions of these muscles manifest concomitantly. Additionally, eyebrow raising is seen in hemifacial FABBRINI ET AL. february 2009 vol 5 no 2


spasm, caused by contraction of the frontalis muscle ipsilateral to the facial spasm (the ‘other Babinski sign’); this symptom is the opposite to the eyebrow lowering seen during eyelid closure in blepharospasm.23 Furthermore, the synkinesis during voluntary facial movement that occurs in hemifacial spasm is not evident in blepharo spasm. The aforementioned sensory tricks that patients with blepharospasm use to ameli orate dystonic movements can distinguish this disorder from eyelid tics, which are nonrhythmic and can be partially suppressed by voluntary effort. Neurophysiological studies demonstrate that increased excitability of the R2 component of the blink reflex is a common finding in blepharospasm but not in eyelid apraxia.4,11 The treatment of choice for blepharospasm is injection of botulinum neurotoxin (BoNT) into the orbicularis oculi muscle (Table 3).24,25 Injection of BoNT into this muscle—usually in the orbital and preseptal region—can produce a 90–95% improvement in symptoms and the benefit is maintained after many years of treatment.25 Pharmacological therapy with anti cholinergics, benzodiazepines or tetrabenazine only rarely improves blepharospasm. Selective peri pheral denervation or orbicularis oculi myectomy can be considered in the occasional patients who do not respond to BoNT injection.26 Eyelid apraxia

Eyelid apraxia occurs in two forms—apraxia of eyelid opening and apraxia of eyelid closure. Apraxia of eyelid opening is characterized by transient inability to initiate, and/or failure to sustain, eyelid elevation, in the absence of overt orbicularis oculi muscle contraction (Table 1).27 With apraxia of eyelid opening, no oculomotor or ocular sympathetic nerve dysfunction or ocular myopathy is present. During episodes of eyelid closure, patients typically elevate their eyebrows in an attempt to open the eyelids. Patients sometimes use a finger to help open the eyelids (either by prising open the lid or as a sensory trick). The episodes of eyelid closure and the delay in eyelid reopening that characterize apraxia of eyelid opening can stem from involun tary muscle contractions that are restricted to the pretarsal portion of the orbicularis oculi (pretarsal or atypical blepharospasm) or from transient involuntary inhibition of the levator palpebrae superioris muscles. Apraxia of eyelid opening can occur in isolation or in association with blepharospasm or atypical parkinsonism. In

A

B

Figure 1 Images of a patient affected by blepharospasm. (A) and (B) show different phases of an involuntary bilateral orbicularis oculi muscle contraction.

patients with Parkinson disease, apraxia of eyelid opening can be induced by deep brain stimulation of the subthalamic nucleus.10 The isolated form of apraxia of eyelid opening usually starts between the fifth and seventh decades of life and the disorder affects more women than men.28 A delay in eyelid reopening typically associated with bilateral eyebrow elevation distinguishes isolated apraxia of eyelid opening from blepharo spasm and can help to identify this condition.27 Injection of BoNT into the pretarsal part of the orbicularis oculi muscles (the mid-upper eyelid close to the eyelash line) improves clinical symptoms in patients with apraxia of eyelid opening (Table 3).29 Apraxia of eyelid closure is characterized by transient inability to close the eyelids voluntarily. This condition can result from right-sided frontal cortex lesions of various origin or from progressive supranuclear palsy30 and is considered to be a supranuclear lid dysfunction. In the differential diagnosis, apraxia of eyelid closure should be distinguished from other supranuclear disorders of lid movements, such as ‘motor impersistance’, which is characterized by inability to keep the eyes closed for more than a few seconds. No specific treatment is available for apraxia of eyelid closure, but patients try to overcome the lid disturbance by use of a variety of synkinetic movements. Movement disorders that affect the face Dystonia

Dystonia is characterized by sustained muscle contractions, which lead to twisting and repetitive movements,11 and this disorder can affect the face in several conditions. In the majority of

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Table 2 Cranial movement disorders that affect the face. Disorder

Pattern

Activation profile

Associated features

Dystonia

Stereotypic

Spontaneous; worsened by voluntary movements

In primary forms, dystonia also in other body parts In secondary forms, other CNS pathological conditions

Drug-induced dyskinesia

Stereotypic

Spontaneous; worsened (levodopainduced dyskinesia) or improved (tardive dyskinesia) by voluntary movements of affected muscles

In levodopa-induced dyskinesias, dyskinesia present also in other body parts

Tics

Repetitive

Spontaneous, or induced by emotional stimuli

Voluntary suppression

Chorea

Nonrepetitive

Spontaneous, or induced by voluntary movements

Choreic movements in other body parts

Myoclonus

Stereotypic

Spontaneous, or induced by voluntary movements or reflex stimuli

Other CNS pathological conditions

Myokymia

Stereotypic

Spontaneous

Brainstem lesions (sometimes)

Hemifacial spasm

Unilateral (in rare cases bilateral); Stereotypic

Spontaneous, or induced by voluntary movements

Other Babinski sign, facial paresis (postparalytic hemifacial spasm)

Myotonia

Stereotypic

Induced by voluntary movements

Other usual features of muscle disease

Neuromyotonia

Stereotypic

Spontaneous; worsened by voluntary movements

NA


patients with Wilson disease, dystonia causes a prominent facial grimace (the ‘sardonic smile’, or ‘risus sardonicus’) that is usually accompanied by dystonia in other body parts.31 An action dystonia of facial muscles that is characterized by frontalis and platysma contraction and gives a startled appearance is common in patients with neuroferritinopathy.32 Acute dystonic reactions to drugs can involve the facial muscles, producing grimacing and additional contractions of the jaw, tongue and neck muscles, and presence of oculogyric crises.33 Neurophysiological studies in these conditions are lacking. Therapy for acute dystonic reactions involves withdrawal of the offending drug (usually a neuroleptic agent) and use of anticholinergics or benzodiazepines. Drug-induced dyskinesia

Facial dyskinesias are involuntary, repetitive and random movements of the muscles of facial expression that manifest as an ever-changing combination of frowning, eyelid elevation, blinking, grimacing, lip pouting, puckering, smacking, blowing, puffing, whistling and sucking movements. Tardive orofacial dyskinesias (TDs), which are induced by chronic use of dopamine 96 nature clinical practice neurOLOGY

receptor blocking agents,34 are typically focused on the oral–buccal–lingual area, with chewing, lip smacking, lip puckering, and twisting or protrusion of the tongue, usually without involvement of other body parts. These dyskinesias are often accompanied by breathing noises, sighing and grunts (Table 2). TDs are common in outpatients with psychiatric disorders, among whom they have an incidence of up to 20%;35 however, the use of atypical antipsychotics has reduced the risk to about one-third of that seen with traditional neuroleptics, as demonstrated by a metaanalysis.36 The most important risk factors for TD are increased age and duration of exposure to dopamine receptor blocking agents.35 Treatment of TDs involves withdrawal of the offending drugs and their replacement with atypical neuroleptics or with dopamine-depleting agents such as tetra benazine. Other therapies that can be used include benzodiazepines and vitamin E (Table 3). Levodopa-induced dyskinesias (LIDs) are seen in patients with Parkinson disease. These dyskinesias commonly affect the face, sometimes have dystonic features, and are nearly always associ ated with involuntary movements in other parts of the body (Table 2). After 5 years of levodopa FABBRINI ET AL. february 2009 vol 5 no 2


treatment, about 40% of patients with Parkinson disease develop LIDs; LIDs are most common in patients with young-onset disease.37 Levodopainduced dyskinesias of the lower face, lips and platysma that resemble risus sardonicus can develop in patients with multiple system atrophy, often in the absence of limb dyskinesias or marked clinical improvement of motor signs.38 In patients with Parkinson disease, LIDs are managed through readjustment of the dopa minergic agent and/or its dose and adminis tration of amantadine or clozapine (Table 3). Deep brain stimulation of the globus pallidum and subthalamic nucleus is also an effective strategy. No specific treatments exist for LIDs in patients with multiple system atrophy. The clinical features of facial involvement in TDs and LIDs can resemble those seen in Huntington disease, and Huntington disease should, therefore, be considered in the differential diagnosis. Huntington chorea involves the forehead and eyebrows more than the perioral musculature, whereas the converse pattern is more frequently observed in TDs and LIDs.39 Motor impersistence of the tongue is common in chorea but is not usually seen in TDs. Grimacing movements with lip biting, tongue protrusion during eating and vocalizations should raise the suspicion of neuroacanthocytosis40 or Lesch–Nyhan syndrome. Tics

Tics are brief, rapid, nonrhythmic movements that patients can willfully suppress at certain times. Tics commonly affect the face, causing eye blinking, eyebrow raising, darting of the eyes, grimacing, mouth opening, tongue protrusion, platysma contractions, and twitching of the nose (Table 2). Tics can have a dystonic component, with ocular deviation, bruxism, mouth opening, and eye closure that mimics blepharospasm.41 Facial tics can occur in isolation but are usually accompanied by tics in other parts of the body. Tics are most prevalent between the ages of 9 and 11 years. The condition occurs predominantly in males and children with psychiatric comorbidities or educational problems, and its overall prevalence is estimated to be 6–12%.42 Facial tics can occur as an isolated phenomenon or as part of Tourette syndrome. Tics, including Tourette syndrome, have a genetic basis,43 but secondary forms of tics are recognized. Post-infectious autoimmune mechanisms have recently emerged as contributing factors in some cases.44 february 2009 vol 5 no 2 FABBRINI ET AL.

Table 3 Treatments for cranial movement disorders. Disorder

First choice

Other therapies

Blepharospasm

Botulinum neurotoxin injection into the orbicularis oculi muscle (orbital and preseptal part)

Neurectomy or myectomy Anticholinergics Benzodiazepines Tetrabenazine

Apraxia of eyelid opening

Botulinum neurotoxin injection into the orbicularis oculi muscle (pretarsal part)

NA

Tardive dyskinesias

Withdrawal of neuroleptic drugs

Atypical neuroleptics Tetrabenazine Benzodiazepines Vitamin E

Levodopainduced dyskinesias

Modification of dopaminergic treatment

Amantadine Clozapine Deep brain stimulation

Tics

Botulinum neurotoxin injection Neuroleptics

Tetrabenazine α2-Adrenergic agonists Clonazepam Nicotine gum

Chorea

Neuroleptics Tetrabenazine

NA

Myoclonus

Valproate Benzodiazepines Barbiturates Piracetam, levetiracetam

NA

Myokymia

Botulinum neurotoxin injection

NA

Hemifacial spasm

Botulinum neurotoxin injection into the orbicularis oculi muscles and into the lower facial muscles

Gabapentin Carbamazepine Benzodiazepines Microvascular decompression of the facial nerve at the cerebellopontine angle

Myotonia and neuromyotonia

Anticonvulsants Membrane stabilizers

NA

Oromandibular dystonia

Botulinum neurotoxin injection into the jaw-closing and jaw-opening muscles

Anticholinergics Benzodiazepines Tetrabenazine Deep brain stimulation

Jaw tremor in Parkinson disease

Levodopa, dopamine agonists

Anticholinergics

Jaw tremor in essential tremor

β-Blockers, primidone

Clonazepam Gabapentin Topiramate

Hemimasticatory spasm

Botulinum neurotoxin injection into the masticatory muscles

NA

Edentulous dyskinesias

Insertion of dentures Occlusal treatment

NA

Tongue-protrusion dystonia

NA

Botulinum neurotoxin injection into the genioglossus muscles Deep brain stimulation

Palatal tremor

Botulinum neurotoxin injection into the levator veli palatini muscle

Clonazepam

Dystonia in Wilson disease

Standard medical treatment

NA


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In patients with facial tics, the blink and startle reflexes indicate increased excitability of brain stem interneurons.45 Functional neuroimaging studies (functional MRI, single-photon-emission CT [SPECT] and PET) indicate that a nonspecific pattern of increased motor cortical activity— such as is also seen in other hyperkinetic disorders—might occur that involves cortical– striatal–thalamic–cortical loops.46 Within this cortical network, the cingulate cortex innervates the upper face bilaterally and receives projections from the limbic lobe and amygdala, conveying emotional expressions to the facial muscles.47 In the differential diagnosis, tics must be distinguished from habitual facial gestures or mannerisms that are evident in the general population, as well as from facial stereotypies in patients with neuropsychiatric conditions. The major distinguishing clinical feature of tics is their stereotyped pattern, which contrasts with the random distribution of facial chorea. The fact that tics can be suppressed by an effort of will also distinguishes these movements from chorea and myoclonus. The differential diagnosis of tics also includes clonic eyelid movements in blepharospasm. Tics can be treated with neuroleptic drugs or with dopamine-depleting agents such as tetrabenazine.48 Other therapies include α2-adrenergic agonists, clonazepam and nicotine gum. Deep brain stimulation of the subthalamic nucleus can be a useful treatment for tics in very severe cases of Tourette syndrome.49 When tics selectively affect facial muscles, BoNT injection into the most affected muscles can be useful (Table 3).50 Chorea

Chorea is defined as spontaneous, flowing movement that is irregular in timing and randomly distributed, spreading from one part of the body to another, including the face (Table 2). The upper and lower facial chorea that is seen in Huntington disease is particularly striking and is always associated with chorea of the trunk and limbs. The orofacial chorea that occurs in patients with neuroacanthocytosis can be associ ated with vocalizations, tongue and lip biting and a characteristic lingual eating dystonia.40 Chorea in facial muscles can also be seen in other rare causes of secondary choreas.39 A study has shown reduced excitability of the R2 component of the blink reflex in patients with Huntington disease.51 The reduced R2 98 nature clinical practice neurOLOGY

excitability correlated with the severity of facial choreas and was possibly related to a defective control of reflex motor responses induced by sensory inputs.52 In patients with facial choreic movements owing to Huntington disease, MRI findings show the typical picture of caudate atrophy present in this disease.39 Diagnosis of other causes of facial chorea is made mainly on the basis of medical history and laboratory investigations.39 Facial chorea can be treated with neuroleptic drugs or with dopamine-depleting agents such as tetrabenazine (Table 3).48 Myoclonus

Facial myoclonus is characterized by sudden, shock-like involuntary movements caused by brief muscle contractions (Table 2). The clinical pattern varies widely from unilateral jerks to bilateral and more-generalized myoclonus that involves other body parts. Action myoclonus of the face (during speech) and blepharoclonus (during blinking) are promi nent in postanoxic myoclonus. In addition, myoclonus that affects muscles innervated by the cranial nerves can be present in patients with essential myoclonus or myoclonic dystonia.53 Brainstem myoclonus, which can occur as part of either a pathological startle response or the neck retraction reflex,54,55 is characterized by sequential activation of the cranial muscula ture, consistent with the presence of a central pattern generator in the caudal brainstem. Facial myoclonus can also be prominent in serotonin syndrome (an extreme adverse drug reaction to serotonergic agents). Facial myoclonus commonly heralds the secondary generalization of a motor seizure but is occasionally the main manifestation of focal epilepsy or epilepsia partialis continua. Myoclonus can originate from several levels of the motor system (the cortex, brainstem, spinal cord, or peripheral nerves), and the clinical and electrophysiological features depend on the level affected. Neurophysiological studies, including simultaneous electroencephalography–electro myography recordings and investigation of brainstem reflexes, can clarify the level involved. Facial myoclonus of brainstem origin is usually associated with generalized jerks and is sensitive to cutaneous and auditory stimulation.54 The typical shock-like contraction of myoclonus differentiates myoclonic jerks from tics, myokymia and hemifacial spasm. Valproate, piracetam, levetiracetam, benzodiazepines and FABBRINI ET AL. february 2009 vol 5 no 2


barbiturates can all be helpful in the treatment of myoclonus (Table 3).53 Myokymia

Facial myokymia is characterized by continuous, undulating rippling of the face (Table 2). The rippling is often associated with a subcutaneous sensation. Myokymia of the orbicularis oculi muscle is common in fatigued healthy indivi duals, but facial myokymia should alert the clinician to the possibility of a pontine lesion (present in multiple sclerosis or pontine glioma), peripheral neuropathy,56 or, in rare cases, an inherited disorder.57 Facial myokymia is generated by hyper excitability of facial motor neurons at any level and is identified by characteristic doublet or triplet motor unit discharges on EMG. The continuous undulating motion of myokymia distinguishes this movement disorder from tics and myoclonus. Injection with BoNT can alleviate the symptoms of myokymia (Table 3).24 Hemifacial spasm

Hemifacial spasm is characterized by involuntary contractions of the upper and lower facial muscles, including the platysma (Table 2). The predominantly clonic form of hemifacial spasm is characterized by brief and repetitive contractions of facial muscles, whereas the predominantly tonic form of hemifacial spasm is characterized by sustained contractions of these muscles. Tonic hemifacial spasm leads to facial-muscle contractures, which create the impression in a face at rest that the normal side of the face is weak, until voluntary facial movement reveals synkinesias on the affected side. Patients with hemifacial spasm sometimes manifest the other Babinski sign—that is, eyebrow raising caused by contraction of the frontalis muscle ipsilateral to the spasm.23 Hemifacial spasm is typically unilateral (