Hemifacial spasm (HFS) is a neurological disorder manifested by twitching spasms on one side of the face due to involuntary contractions of the eyelid and other facial muscles. It usually begins gradually around one eye and may eventually spread to include the muscles around the mouth and neck on the same side. These muscle spasms are very brief but occur rapidly and repetitively. They are generally not painful, but may impact vision because of involuntary eye closure. In contrast to blepharospasm, a form of focal dystonia, which is associated with eyelid spasms involving both eyes, HFS involves only one side of the face. Very rarely, both sides of the face may become affected in HFS, but the contractions remain asymmetric and independent of each other. The facial spasms are often noticed by others and can be a source of embarrassment to the patient. They may even be wrongly thought of by others as winking. HFS can sometimes be triggered by volitional contraction of certain facial muscles, especially puckering the lips or after forcefully closing eyes. Stressful situations or fatigue may also worsen the spasms. Estimates suggest that one in ten thousand people have HFS and it usually presents in the 5th or 6th decade. It may be somewhat more common in women than men and is more frequently seen in the Asian population.
HFS usually appears without obvious cause but it is most often attributable to a compression of the facial nerve as it exits from the brainstem. This nerve supplies muscle power to the facial and superficial neck muscles. In most cases the compression is from a hardened and/or displaced blood vessel near the base of the brain. Rarely, aneurysms, brain tumors or trauma may also compress the facial nerve. The compression then causes the nerve to "short circuit" and fire independently, a phenomenon referred to as ephaptic transmission. When the nerve fires, the signal is misdirected to other parts of the nerve causing muscle contractions in different areas of the face on the same side. A competing hypothesis states that hemifacial spasm is due to abnormality of the facial motor nucleus in the brainstem. This has been supported by studies of the blink reflex. Further research is needed to elucidate the pathophysiology of this disorder.
In some cases, the condition occurs months or even years after an episode of unilateral facial weakness known as Bell's palsy. In this case, it is called post-paralytic hemifacial spasm. Involuntary contractions involving muscles adjacent to those that contract voluntarily, termed synkinesis and other features usually readily differentiate typical HFS from spasm that occur following recovery from Bell's palsy. Bell's palsy is usually caused by a virus which resides in one part of the facial nerve. The damaged nerve later grows back imperfectly resulting in short circuits and spontaneous firing.
An experienced neurologist can usually diagnose HFS by simply observing it and an electrical nerve study known as an EMG is rarely needed. If performed, however, it will show irregular, brief high-frequency burses (150-400 Hz) of motor unit potentials, which correlate with the clinically observed facial movements. If atypical features such as facial numbness or hearing loss are present, then a neuroimaging study, such as an MRI or MRA, may be useful.
Currently, most physicians consider botulinum toxin injections to be the optimal treatment. This protein is injected directly into the affected muscles. At relatively low doses, it relaxes the affected muscles enough to prevent the spasms without causing paralysis. The improvement occurs within 3-4 days and lasts an average of 4-6 months. Repeat injections are then required at varying intervals depending on each individual's response. In the hands of a well-trained practitioner, the procedure is very safe. Potential side effects include an eyelid droop (ptosis), facial weakness or increased tearing, all of which resolves over time. Microvascular decompression of the facial nerve is also considered a feasible and effective method of treatment, but in the presence of alternative therapy, should be performed with low risk to the patient. Medications used for seizures such as carbamazepine, phenytoin and clonazepam, and muscle relaxing medications such as diazepam, baclofen and trihexyphenidyl, are only rarely helpful. Also, their use is often associated with adverse side effects. A neurosurgical procedure known as microvascular decompression sometimes called the Jannetta procedure, is not needed as much as in the past but is still employed in refractory cases. While it has a favorable long-term outcome, it is an involved procedure requiring general anesthesia in order to remove of a portion of the skull, expose the brainstem and dissect the offending blood vessel away from the facial nerve. It has potential for serious complications, including facial weakness, deafness and stroke.
Benign Essential Blepharospasm Research Foundation
P.O. Box 12468
Beaumont, TX 77726-2468
Phone: (409) 832-0788
Fax: (409) 832-0890
©2011 Joseph Jankovic, M.D.
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