2.4 Hemifacial Spasm
By Jordan Dattero; Lilah Keating; and Raymond F. Sekula, Jr., MD (USA)
Hemifacial spasm (HFS) is characterized by irritating repeated spasms of the facial muscles in half of the face and a sense of fatigue when they occur. Individuals with HFS have described the sensation as feeling as if someone is pulling on half of their face. When asked, they have also described HFS as having constant pressure in their heads and feeling complete relief only post-surgery. Although the spasms are intermittent, over time, their duration can lengthen, and the spasms can become seemingly continuous. As for other neurological disorders, patients report that their spasms are sometimes triggered by anxiety, fatigue, or stress. The forceful spasms may cause involuntary, intermittent eye closure that leads to a loss of binocular vision. This becomes hazardous when actions such as driving can suddenly be impaired when unpredictable spasms occur, and half of the patient’s vision is affected. It has been reported that sleeping and reading also become more difficult with the condition. HFS can also cause psychological distress, anxiety, and depression, as those experiencing the condition often isolate themselves from professional and social opportunities because of embarrassment from the uncontrollable spasms or concern that the spasms deem them unfit to perform certain tasks. When the spasms occur, the resulting facial asymmetry often elicits unwanted attention from observers. As the condition worsens over time, patients may experience partial closure of their eye and drawing up of the corner of their mouth. It is also common for patients to say that they hear new noises, a phenomenon likely caused by pulsations of the cochlear or facial nerve.
HFS is a rare condition that occurs in 9.8 per 100,000 people. An estimated 14.5 per 100,000 women and 7.4 per 100,000 males develop the disorder. Thus, women are twice as likely to be affected by HFS as are men. Asian populations are overrepresented among those with HFS. Onset occurs at an average age of 44 years. There have been a few reported cases of HFS as a genetic condition. However, in these cases, HFS exhibits autosomal dominant inheritance and low penetrance.
Diagnosis of HFS is based on clinical history and neurological examination. The spasms usually begin with the orbicularis oculi muscle (i.e., the eyelid muscles), but as HFS progresses, the spasms spread to the cheek and oral muscles. EMG helps distinguish this disorder from other similar disorders such as blepharospasm, tics, partial motor seizures, synkinesis, craniocervical dystonia (formerly known as Meige’s syndrome), and neuromyotonia. For diagnosis and treatment, one must undergo a comprehensive medical evaluation and contact a medical professional who can discuss the treatment options.
HFS is caused by pulsatile vascular contact or compression of the facial nerve near the brain stem. Commonly, the anterior inferior cerebellar artery (AICA) or posteroinferior cerebellar artery is responsible. Compression from the artery, blood vessel, or tumor can also cause hyperactivity of a cluster of facial nerves within the brain stem, which further contributes to the facial spasms. In rare cases, compression of the nerve by a tumor or other problems can result in facial spasms. A high-resolution MRI scan of the brain performed using one of the special techniques known by the acronyms FIESTA and CISS and with gadolinium dye infusion will identify any vascular contact with the facial nerve or show a tumor or any other structural lesions.
Since the early 1980s, injections of botulinum neurotoxin (BoTN, also called Botox) have become the most common treatment for HFS. BoTN offers a nonsurgical treatment to provide some symptomatic relief in 92% of patients. BoTN provides relief from HFS by blocking the release of acetylcholine at the synaptic neuromuscular junction. In turn, without acetylcholine, the muscles cannot receive the nerve’s impulses, and therefore, spasms are reduced. Effectively, BoTN injections reduce muscle activity by creating drug-induced muscle weakness.
BoTN injections have only a short-term relief period and have associated risks. After injection, the severity of spasms declines over a few weeks. However, symptoms tend to return within 4 months. Possible complications can include ptosis, blurred vision, and diplopia, all of which usually resolve within a few days or weeks. Repeated injections can lead to facial weakness and atrophy of the facial muscles. In this case, injection of the opposite side of the face may be used to achieve cosmetic effects. HFS tends to be a progressive disorder in which spasms become more frequent and intense over time. As minor contractions such as eyelid twitches may be effectively treated with BoTN, full-face contraction proves less effective to control with injections.
Once a blood vessel has been confirmed to be contacting or compressing the facial nerve by MRI, MVD surgery can be considered with a goal of removing the vascular contact.
MVD of the nerve can be performed by interposition or transposition of the nerve. At the time of this writing, neither technique has been shown to be superior to the other. Interposition can be used when perforators that supply blood to the brain stem are coming from the compressive blood vessel. To avoid injury to these perforators, polytetrafluoroethylene (PTFE) felt may be interposed between the blood vessel and the nerve, acting as a cushion that separates the blood vessel from the nerve and thus alleviating the pressure. Transposition is when the blood vessel is moved away from the nerve and affixed to a remote area. Neurosurgeons cannot assess whether they need to transpose or simply interpose a blood vessel until reaching the compression site during surgery and observing whether the blood vessel has perforators. In some instances, appendage slings are attached to the petrous dura to ensure that the problematic vessel is separated from the nerve; however, this is not always necessary.
A difficult component of the surgery is when the operative field is narrow for reasons such as a large flocculus (a normal brain structure) or an unideal location of the sigmoid sinus. In most MVD surgeries, the conventional retrosigmoid approach, in which the brain is entered from behind the ear, is used. However, when the operative field is narrow, alternative surgical approaches such as the extended retrosigmoid approach or the Retrolabyrinthine presigmoid approach can be used to gain better access to the site of compression. This just means that certain factors alter the best approach into the brain and provide sufficient access to the site of compression.
As with any surgery, there are some risks to MVD surgery, although they are low. The most common risks are facial weakness and partial hearing loss or deafness (1.5% of cases). Hearing loss may be lessened using brain-stem auditory evoked potential (BAEP) monitoring during the MVD operation to alert surgeons of cochlear nerve damage. An additional risk is leakage of the cerebrospinal fluid (CSF), which can lead to infection. CSF leaks can cause headaches, neck pain, ringing in the ears, loss of smell or taste, and meningitis. To avoid this complication, calcium phosphate cement can be used during the closure of the retromastoid craniectomy in surgery. A retrospective study using clinical data from 672 patients suggested that this decreases the rate of CSF complications, infection, or any other wound complications. Other low-probability complications include stroke, cerebellar hematoma, other cranial nerve injury, and death. Overall, serious complications in MVD surgery for HFS occur in less than 1% of cases, and recurrence can occur in 4% to 10% of patients. (Kaufmann 2023, Sekula 2013)
Despite a higher risk of complications, MVD is the only curative treatment. Additionally, patients who undergo this operation have exhibited a significant positive psychological impact. Many describe the success of surgery as the ability to regain confidence and restore engagement in daily interactions and relationships. This improved quality of life (QOL) was measured using a QOL questionnaire with unique questions related to the experiences of HFS patients. A retrospective study analyzed 242 patients who had undergone MVD surgery. The mean score improved from 22.78 (± 9.83) down to 2.17 (±5.75) following the operation. (Lawrence 2018)
Why is MVD surgery so uncommon? A likely reason is that only 10% of individuals with HFS are referred to neurosurgeons. Most patients who wish to undergo MVD surgery are self-referred people who determined that MVD was a viable treatment option after doing their own research.
MVD surgery has proven to be successful in reducing long-term spasms in about 92% of cases, with low morbidity and mortality rates. Because of the rarity of this condition, the failure rate for the surgery is higher than it should be, perhaps because of the lack of specialized expertise in those who perform the surgery. Success rates of MVD for HFS are commonly derived from high-volume centers. The best course of action is to consult a surgeon who is an expert in this operation and performs many such surgeries each year.
Although it is up to the patient to determine which course of action they wish to pursue based on the severity of the condition and its impact on their QOL, the most sustainable and curative treatment option for most is MVD surgery. BoTN injections provide temporary relief and reduce the frequency and intensity of the spasms. This treatment would be most appropriate for individuals unwilling or unfit for surgery or a general anesthetic; yet, for most it is not a long-term solution. Additionally, when considering long-term costs, it is more cost-effective to opt for surgery than to continue with BoTN injections every few months indefinitely. See a neurosurgeon with experience. Ask questions. Listen to the answers. See Section 3.1 in the next chapter on what makes a neurosurgeon an expert for more advice.
