eMedicine Specialties > Neurology > Neuromuscular Diseases

Hemifacial Spasm

Author: Steven Gulevich, MD, Department of Neurology, Swedish Medical Center of Englewood, Colorado
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Updated: Feb 3, 2009

Introduction

Background

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.

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.

Pathophysiology

First described by Gowers in 1884, hemifacial spasm (HFS) represents a segmental myoclonus of muscles innervated by the facial nerve. The disorder 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).

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.

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.

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.

Race

All races are affected equally.

Sex

A slight female preponderance exists in hemifacial spasm.

Age

• 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).

Clinical

History

Involuntary facial movement is the only symptom. Fatigue, anxiety, or reading may precipitate the movements.

• Hemimasticatory spasm
  • Hemimasticatory spasm is analogous to hemifacial spasm and occurs with irritation to the motor trigeminal nerve.
  • This rare condition is a segmental myoclonus and presents with unilateral involuntary contractions of the trigeminally innervated muscles of mastication (usually the masseter).
  • Similar to hemifacial spasm, hemimasticatory spasm responds to treatment with medications and botulinum toxin.
  • However, less evidence exists that exploratory surgery benefits patients with this condition.
• Myoclonic movements
  • Myoclonic movements affecting facial musculature also may arise from lesions at the brain or brainstem level.
  • These are distinguished from hemifacial spasm by the distribution of abnormal movements (more generalized, possibly bilateral) and possibly by electrodiagnostic evaluation.
  • Imaging studies may yield an underlying cause.
  • Central myoclonus responds to anticonvulsant management.
• Oromandibular dystonia
  • Oromandibular dystonia (OMD) refers to dystonia affecting the lower facial musculature, predominantly the jaw, pharynx, and tongue.
  • When oromandibular dystonia occurs in conjunction with blepharospasm, the disorder is termed Meige syndrome.
  • Jaw-opening forms of oromandibular dystonia indicate primary involvement of the digastric and lateral pterygoid. Jaw-closing oromandibular dystonia involves the masseter, temporalis, and medial pterygoid.
  • Jaw deviation, indicating predominant involvement of the lateral pterygoid, is rare.
  • Botulinum toxin is the preferred treatment for oromandibular dystonia and is most effective in the jaw-closure type.
  • Medications seldom yield acceptable results. When medications must be used, employ the same agents as for blepharospasm.
  • Because of the risk of aspiration, never inject botulinum toxin into the tongue.
• Craniofacial tremor
  • Craniofacial tremor may occur in association with essential tremor, Parkinson disease, thyroid dysfunction, or electrolyte disturbance.
  • It occurs rarely in isolation.
  • Focal motor seizures must occasionally be distinguished from other facial movement disorders, particularly hemifacial spasm.
  • Postictal weakness and greater involvement of the lower face are distinguishing features of focal motor seizures.
• Facial chorea
  • Facial chorea occurs in the context of a systemic movement disorder (eg, Huntington disease, Sydenham chorea).
  • Chorea is a random, flowing, nonpatterned set of movements.
  • A related disorder, spontaneous orofacial dyskinesia of the elderly, is observed primarily in the edentulous. It usually responds to proper fitting of dentures.
• Tics
  • Facial tics are brief, repetitive, coordinated, semipurposeful movements of grouped facial and neck muscles.
  • Tics may occur physiologically or in association with diffuse encephalopathy.
  • Some medications (ie, anticonvulsants, caffeine, methylphenidate, antiparkinsonian agents) are associated with producing tics.
  • Single, repetitive, stereotyped movements (eg, repetitive grimacing, throat clearing, vocalizations) define a simple tic disorder.
• Facial myokymia
  • Facial myokymia appears as vermicular twitching under the skin, often with a wavelike spread.
  • This is distinguished from other abnormal facial movements by characteristic electromyogram discharges presenting as brief, repetitive bursts of motor unit potentials firing at 2-60 Hz interrupted by periods of silence of up to a few seconds.
  • Facial myokymia may occur with any brainstem process. Severe cases may benefit from botulinum toxin.
  • Most cases are idiopathic and resolve without treatment over several weeks.

Physical

• The only physical finding in hemifacial spasm is involuntary facial 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 palsy) manifests as facial synkinesis and contracture.

Causes

• Idiopathic
• Vascular compression
• Facial nerve compression by mass
• Brainstem lesion such as stroke or multiple sclerosis plaque
• Secondary to trauma or Bell palsy

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