Hemifacial spasm (HFS) is characterized by intermittent, involuntary twitching of the muscles in one side of the face, which can last from a few seconds to several minutes. Spasms occur spontaneously and without warning. They are often exacerbated by stress or fatigue, but can also be triggered by stimuli like sunlight, touch, chewing, and talking. Spasms do not cause pain, but can cause discomfort, impaired vision due to forced eye closure, as well as social discomfort and embarrassment.
The spasms usually begin with involvement of muscles around the eye. Over time, spasms usually intensify and extend further down the side of the face to include the cheek and mouth areas. In severe cases, spasms can also involve the forehead and neck. As HFS progresses, it not only involves an increasing area on the affected side, but the intensity of the spasms increases as well.
A less common form of HFS, termed atypical HFS, involves the onset of spasms in the lower face and tends to be more difficult to treat.
Another form of HFS, called post-paralytic HFS, may develop following facial paralysis from injury, trauma, or Bell's Palsy. In post-paralytic HFS, voluntary facial contractions are usually accompanied by involuntary spasms elsewhere on the face, called intrafacial associated movements.
Diagnosis of typical HFS is based upon a clinical history of reported symptoms and an otherwise normal neurological and cranio-facial examination. Magnetic resonance Iimaging (MRI) may demonstrate compression of the facial nerve by a blood vessel or tumour, although most imaging studies yield normal results. Electromyogram (EMG), which tests the electrical functioning of the nerve, can demonstrate the abnormal nerve activity characteristic of HFS, although it is rarely necessary in order to diagnose the disease.
The onset of HFS most often occurs in middle age, although less than 1% of HFS cases develop before age 30. The annual rate of HFS increases with advancing age, but on average, the incidence is 0.8 cases per 100,000 people each year. Women are affected almost twice as often as men. HFS is not thought to be hereditary.
What causes HFS?
There are twelve pairs of cranial nerves. The seventh (VII) or facial nerve controls all facial movements. The nerve originates in the facial nerve nucleus of the brain stem, and branches of the nerve extend to all parts of the face, including the forehead, eye, cheek, mouth, and neck. HFS is caused by hyperactivity of the facial nerve system.
HFS is typically caused by a blood vessel that is pulsating against the facial nerve root as it leaves the brain stem. This irritation causes abnormal signals to travel back to the facial nerve nucleus within the brain stem. These abnormal signals cause the nucleus to become hyperactive. The hyperactive facial nerve nucleus then sends signals to the face, which cause the abnormal facial movements of HFS.
In technical terms, HFS is typically caused by neurovascular compression of the facial nerve root entry zone (peripheral pathology) and a resultant hyperactivity of the facial nerve nucleus (central pathophysiology).
In people without HFS, there is no vascular compression upon the facial nerve root exit zone.
In people with HFS, a vessel is usually found to be pulsating against the facial nerve root exit zone.
Overview of Treatments
Hemifacial spasm usually begins with mild spasm involving the small muscles around the eye. These may be controlled by medications such as Tegretol® or Dilantin®, but medical therapy alone is usually not effective in providing long-term spasm control. The two treatment options most widely considered are repeated Botulinum toxin (Botox®) injections or microvascular decompression (MVD) surgery. There are strong proponents of both intervention, although HFS sufferers should make their own decisions based on a thorough understanding of the usual disease course, as well as the potential advantages and disadvantages of each treatment.
Botulinum toxin (Botox®) is a purified form of the neurotoxin, which is produced by the bacteria Clostridium botulinum that causes botulism. Small doses of Botox® may be injected into muscles, causing temporary weakness or paralysis in the injected areas. In HFS, Botox® may be injected into the affected muscles to block spasms. The drug effect wears off after two to three months, and re-injections are then required to regain control of the spasms.
Botox is particularly effective for HFS which involves only the small muscles around the eye. Spasm control is more difficult to obtain when the larger muscles of the lower face become involved. As the severity and extent of HFS progresses over time, the effectiveness of repeated Botox® injections may diminish.
In this diagram, botulinum toxin injections are targeted
at the muscles around the eye.
The neurotoxin Botox® is injected into affected muscles where they attach to nerve endings. This blocks the transmission of nerve signals to the muscles, resulting in muscle weakness or paralysis. However, new nerve endings grow to replace those blocked by the Botox®, and muscle function (including spasms) returns within two to three months. Re-injections are then required repeatedly to regain control of HFS.
Possible side effects of Botox® injections for HFS include drooping of the face, bruising, bags under the eye, and pain at the injection sites. Repeated Botox® injections may induce permanent weakness in the facial muscles. In rare instances, patients may develop a resistance to the botulinum toxin once their bodies have produced antibodies that render the toxin ineffective. This may occur when re-injections are performed over short intervals of time, or when high doses are used. Two types of Botox® are currently manufactured. Type A is the most common form of Botox® used, while the second form, Type B, can be tried in those who have developed a resistance to Type A.
While Botox® has become widely used to treat patients with HFS, the spasms typically worsen over time and become more difficult to control with repeated injections. Therefore, MVD surgery is considered an alternative that offers the potential to cure HFS.
Microvascular Decompression (MVD) Surgery for HFS
Microvascular decompression (MVD) surgery is performed under general anesthesia, through an incision and a small thumbprint sized bony opening behind the ear. An operative microscope is used to visualize the facial nerve root entry zone.
Microsurgical instruments and techniques are used to move the vessels compressing the facial nerve root entry zone and thus alleviate the neurovascular compression. Inert implants of shredded Teflon® are placed so as to move offending vessels and permanently maintain them in their new position away from the facial nerve.
|Prior to MVD.||During MVD, the vessel is mobilized away from the nerve root entry zone.|
|The decompression is maintained with shredded Teflon® felt implants.||MVD has resulted in permanent alleviation of the neurovascular compression.|
When vascular decompression is completed, the dura, the bony opening, and the incision are closed. The patient is then wakened from the anaesthetic and taken to the recovery room. On average, the duration of hospitalization for MVD surgery is three and a half days, and most people return to their full level of activity and employment within two to eight weeks.
Inert shredded Teflon® felt implants
Microvascular decompression of the facial nerve root entry zone eliminates the irritation causing HFS. This allows the hyperactivity of the facial nerve nucleus to settle towards a normal condition. While spasms may disappear immediately after surgery, usually the HFS subsides gradually and is cured over the course of several weeks or months.
In our experience, over 85% of patients with typical HFS are cured with MVD surgery, and another 5-10% have significantly reduced spasms. The risks of surgery have been small, and routine use of intraoperative monitoring (IOM) has been credited with greatly enhancing the safety of MVD. Hearing loss, new weakness of the face, and swallowing difficulties are rare and usually dissipate. Other rare complications include infection, inflammation, and healing difficulty leading to cerebrospinal fluid leak. The risk of serious MVD surgery complications due to stroke, bleeding, or brain swelling are less than 1 in 300.
Intraoperative Monitoring (IOM) during MVD Surgery for HFS
Intraoperative monitoring (IOM) measures small electrical signals produced within the nervous system. These small signals can be ongoing, such as those measured in an EEG, or "evoked" responses produced by stimulating the nervous system, similar to a reflex. In the hands of experienced technologists or physiologists, IOM can reduce the incidence of permanent neurological deficits following neurosurgical procedures such as microvascular decompression (MVD) surgery. IOM can detect subtle changes in nervous system function and provide an early warning to the surgical team so that permanent damage is avoided. This information can guide the surgical team to modify the procedure as necessary in order to improve the outcome and reduce the risk of surgery.
In MVD surgery, IOM personnel place recording electrodes, similar to EKG electrodes, on the patient and connect these to a computerized workstation that records and displays the results of the neurologic tests. Specifically, the Brainstem Auditory Evoked Response is measured for the continuous assessment of the cochlear (hearing) nerve. This nerve is very sensitive to stretch or manipulation, which may result in hearing loss postoperatively. Monitoring of cochlear nerve function alerts the surgical team members to potentially injurious situations and allows them to make adjustments in order to avoid permanent hearing loss.
In addition to the cochlear nearve, other cranial nerves, such as the facial nerve, are also examined. During HFS surgery, the abnormal muscle activity in the facial muscles is continually observed. This not only alerts the surgical team to any threat to the facial nerves' function, but can also indicate when the surgical procedure has relieved the cause of the facial spasm.
For an international online support community for hemifacial spasm sufferers, visit the web site of the Hemifacial Spasm Association.