Hemifacial spasm

Hemifacial spasm (HFS) is defined as unilateral, involuntary, irregular clonic or tonic movement of muscles innervated by the 7th cranial nerve. It is most often caused by vascular loop compression at the root exit zone of the facial nerve.¹

HFS is usually unilateral and sporadic. It may be primary (mainly attributed to vascular compressions of the 7th cranial nerve in the posterior fossa) or secondary to facial nerve or brainstem damage.²

Epidemiology

Prevalence has been estimated at 11 cases per 100,000 individuals. It is more common in middle-aged people and more common in women.³

• Most commonly, vascular compression. Most instances of hemifacial spasm (HFS) previously thought to be idiopathic, were probably caused by aberrant blood vessels compressing the facial nerve within the cerebellopontine angle.⁴

• Idiopathic.

• Facial nerve compression by mass or Paget's disease of bone.

• Meningitis.

• Brainstem lesion such as stroke or multiple sclerosis plaque.

• Secondary to trauma or Bell's palsy.

• Secondary to otitis media with effusion.⁵

The disorder presents in the fifth or sixth decade of life:

• It is usually unilateral, although bilateral involvement may occur rarely in severe cases.

• HFS generally begins with brief clonic movements of the orbicularis oculi and spreads over years to other facial muscles. Closing of the eye and drawing up of the corner of the mouth are typical.

• Involuntary facial movement is the only symptom.

• Fatigue, anxiety or reading may precipitate the movements. Stressful life events are also associated with HFS.⁶

• Mild facial weakness and contraction appear without frank facial palsy.

• There is normal facial sensation.

• There are no other physical signs.

See also the separate article on Abnormal Involuntary Movements.

• Facial myokymia appears as vermicular (worm-like) twitching under the skin:
  

  • There is often a wavelike spread.

  • This is distinguished from other abnormal facial movements by characteristic electromyogram.

  • Facial myokymia may occur with any pathological brainstem process.

  • Idiopathic cases eventually resolve without treatment.

• Myoclonic movements may arise from lesions at the brain or brainstem level.
  

  • They are distinguished from HFS by the distribution of abnormal movements.

  • They tend to be more generalised, possibly bilateral.

• Oromandibular dystonia (OMD) refers to dystonia affecting the muscles of the lower face. When OMD occurs with blepharospasm, it is called Meige syndrome II.

• Craniofacial tremor may occur in association with essential tremor, Parkinson's disease, thyroid dysfunction or electrolyte disturbance. It occurs rarely in isolation.

• Focal motor seizures must occasionally be distinguished from other facial movement disorders, particularly HFS. Postictal weakness and greater involvement of the lower face are its distinguishing features.

• Facial chorea usually occurs within a systemic movement disorder - eg, Huntington's disease.

• Spontaneous orofacial dyskinesia of the elderly is observed primarily in the edentulous. It usually responds to proper fitting of dentures.

• Facial tics are brief, repetitive, co-ordinated, semi-purposeful movements of grouped facial and neck muscles:
  

  • Tics may occur physiologically or in association with diffuse encephalopathy.

  • Tardive dyskinesia - some medications (dopamine agonists) - eg, neuroleptics, anticonvulsants, caffeine, methylphenidate, anti-Parkinsonian agents - are associated with producing tics.

At initial evaluation, consider HFS as a symptom, not a diagnosis:³

• An abnormal neurological examination (except for the facial movements) should prompt the search for an underlying cause - eg, compressive lesion, tumour, stroke.

• Needle electromyogram (EMG) shows irregular, brief, high-frequency bursts (150-400 Hz) of motor unit potentials, which correlate with clinically observed facial movements.

• Magnetic resonance imaging (MRI) is the first-line imaging study.

• Angiography and/or magnetic resonance angiography may be necessary before a vascular surgical procedure.

85-95% of patients obtain moderate or marked relief from local injections of botulinum toxin, which must be repeated every three to four months. Alternatively, microvascular decompression has a success rate of about 85%.³

Pharmacological treatment

Medications may be used in early HFS:

• This is used when spasms are mild and infrequent or in patients who decline botulinum toxin type A injection. Response to medication varies but is generally ineffective.²

• The most helpful agents are carbamazepine and benzodiazepines - eg, baclofen, clonazepam. Topiramate has also been used successfully.⁷

• Often, medication effects attenuate over time, necessitating more aggressive treatment.

In most patients, the treatment of choice is injection of botulinum toxin type A under EMG guidance:⁸

• This is a chemical denervation that safely treats most patients, especially those with sustained contractions.

• It works by binding to receptor sites on the motor nerve terminals and, after uptake, inhibits release of acetylcholine, blocking transmission of impulses in neuromuscular tissue.

• The spasms usually relax three to five days after injection and the effect lasts approximately six months.

• Potential side-effects of botulinum injection are facial asymmetry, ptosis and facial weakness. These are usually transient.

• Most patients are very satisfied with their response to treatment.

• Patients should be warned that although botulinum toxin stops the spasm, the sensation of spasm often persists.

• It is now far more commonly used than surgical intervention.

Surgical treatment

• This usually consists of exploration of the posterior fossa to separate blood vessels from the 7th cranial nerve.

• Microvascular decompression of the facial nerve can provide long-term symptom control in approximately 90% of patients with HFS.⁹

• Operative success is improved with EMG use.¹⁰

• Postoperative complications have been noted in 35% of patients - eg, facial palsy, hearing deficit and low cranial nerve palsies. The more immediate and severe the facial palsy was, the more permanent it remained.¹¹

• Myectomy is rarely ever required.

HFS is a progressive, but non-fatal, illness. It usually responds favourably to treatment. However, it is a chronic disease and spontaneous recovery is very rare.⁸