Hemifacial spasm (HFS) is a neurological disorder manifested by twitching 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 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, 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. HFS can sometimes be triggered by voluntary 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 fifth or sixth decade. It may be somewhat more common in women than in men, and it is more frequently seen in the Asian population.
Diagnosis
An experienced neurologist can usually diagnose HFS by simply observing it, and an electrical nerve study known as an EMG is rarely needed. 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.
Cause
Most cases of HFS do not have an obvious cause and are referred to as “idiopathic”. However, HFS is often attributable to an irritation or a compression of the facial nerve by a blood vessel as it exits from the brainstem and is the most common peripherally induced movement disorder 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. When the facial nerve fires, the signal is directed to the ipsilateral facial muscles causing muscle contractions in different areas of the face on the same side. A competing hypothesis states that HFS is due to abnormality of the facial motor nucleus in the brainstem.
Injuries to the facial nerve can also result in secondary HFS. For example, patients who have had Bell's palsy can develop HFS after they recover from the weakness. The post-Bell’s palsy HFS may look similar to the idiopathic variety, but voluntary contraction of the facial muscles often results in an involuntary contraction of adjacent muscles due to misdirection of the recovering facial nerve and its branches (“synkinesis”). The patients can develop HFS weeks or months after Bell’s palsy. Other uncommon causes of HFS include aneurysms, brain tumors, trauma and demyelinating diseases such as multiple sclerosis.
Treatment
Currently, most physicians consider botulinum toxin (BTX) injections to be the optimal treatment with nearly complete, but transient, improvement in most patients. This protein is injected directly into the affected muscles. When injected by experienced clinician, BTX relaxes the affected facial muscles enough to prevent the spasms without causing paralysis or facial asymmetry. The improvement occurs within three to four days and lasts an average of four to six months. Repeat injections are then required at varying intervals depending on each individual's response. Potential side effects include an eyelid droop (ptosis), facial weakness or increased tearing, all of which resolves over time.
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.
In refractory cases in which there is evidence of compression of the nerve by an abnormal brain vessel, a neurosurgical procedure known as microvascular decompression could be considered. 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. The most common complication is weakness of the facial muscles, which can be noted immediately after the procedure or several days after. Other potential complications include hearing loss, infection, hemorrhage and stroke. Even when successful, many patients experience recurrence, necessitating repeat BTX injections.
References
- Anandan C, Jankovic J. Botulinum Toxin in Movement Disorders: An Update. Toxins (Basel). 2021 Jan 8;13(1):42.
- Chiu SY, Burns MR, Malaty IA. An update on botulinum toxin in neurology. Neurol Clin. 2021;39(1):209-229.
Lenka A, Jankovic J. Peripherally induced movement disorders - an update. Tremor Other Hyperkinet Mov (N Y). 2023 Mar 28;13:8. - Sringean J, Dressler D, Bhidayasiri R. More than hemifacial spasm? A case of unilateral facial spasms with systematic review of red flags. J Neurol Sci. 2019;407:116532.
- Tombasco et al. Botulinum Toxin for the Treatment of Hemifacial Spasm: An Update on Clinical Studies. Toxins (Basel). 2021 Dec 9;13(12):881.
- Tugend M, Ulane CM, Patel K, Sekula RF Jr. Decompression Surgery in Elderly Patients with Hemifacial Spasm Refractory to Botulinum Toxin. Mov Disord Clin Pract. 2024 Aug;11(8):966-972.
