Hemifacial spasm (HFS) is a peripherally-induced movement disorder characterized by the involuntary, unilateral, intermittent, irregular, tonic or clonic contractions of muscles innervated by the ipsilateral facial nerve.
This disease takes two forms: typical and atypical. In typical form, the twitching usually starts in the lower eyelid in orbicularis oculi muscle. As time progresses, it spreads to the whole lid, then to the orbicularis oris muscle around the lips, and buccinator muscle in the cheekbone area.
The reverse process of twitching occurs in atypical hemifacial spasm; twitching starts in orbicularis oris muscle around the lips, and buccinator muscle in the cheekbone area in the lower face, then progresses up to the orbicularis oculi muscle in the eyelid as time progresses.
The most common form is the typical form, and atypical form is only seen in about 2–3% of patients with hemifacial spasm.
The incidence of hemifacial spasm is approximately 0.8 per 100,000 persons.
This disorder occurs in both men and women, although it affects middle-aged or elderly women more frequently.
Hemifacial spasm is much more common in some Asian populations.
The purpose of a study was to characterize the natural history and clinical outcome in patients with HFS.
The initial visits of all 2,155 patients and the diagnosis of HFS took place between 2001 and 2010. In 1,775 of the patients, compressing vessels were identified on magnetic resonance imaging. Of these, we excluded 1,469 patients (82.8%) who received microvascular decompression, 101 (5.7%) who continued to visit the clinic for botulinum toxin injections, and 9 (0.5%) who died or suffered from other diseases. Ninety-two (5.2%) of the patients were lost to follow-up; the remaining 104 were followed up for 5-42 years (mean 12 years) after the onset of the symptoms of HFS.
The condition was aggravated in 11 (10.6%) of the 104 patients and stationary in 40 (38.5%) for 6-42 years (mean 13 years). Ten (9.6%) improved partially for 7-18 years (mean 11 years). Forty-three (41.3%) were in remission for between 2 months and 23 years (mean 6.4 years) after onset and required no further treatment for 5 months to 13 years (mean 5.7 years) 1).
Kindling-like hyperactivity of the facial motor nucleus induced by constant stimulation of compressing artery is considered as the predominant mechanism underlying the pathogenesis of HFS.
In nearly all cases, primary hemifacial spasm is related to arterial compression of the facial nerve at root exit zone (REZ). The offending arterial loops originate from the posterior inferior cerebellar artery (PICA), anterior inferior cerebellar artery (AICA), or vertebrobasilar artery (VB). In as many as 40% of the patients, neurovascular conflicts are multiple. The cross-compression is almost always seen on magnetic resonance imaging combined with magnetic resonance angiography.
Hemifacial spasm (HFS) associated with type 1 Chiari malformation is particularly uncommon and is limited to isolated case report.
Li et al retrospectively evaluated 13 patients who had simultaneously HFS and type 1 Chiari malformation among 675 HFS patients. Clinical features and radiological findings were collected from each patient and analyzed. All these 13 patients were surgically treated with MVD through retro-mastoid microsurgical approach, and postoperative outcomes were evaluated. A review of literature about this association was also provided. In this study, the frequency of type 1 Chiari malformation in HFS patients was 1.9 %. The clinical profile of this series of patients did not differ from typical form of primary HFS. MVD achieved satisfactory results in 11 patients (85 %) in short- and long-term follow-up. There was no mortality or severe complication occurred postoperatively. Although rare, clinician should be aware of the association of HFS and type 1 Chiari malformation and consider MVD as an effective surgical management 2).
Tu et al. used resting state functional magnetic resonance imaging with regional homogeneity (ReHo) analysis to investigate changes in spontaneous brain activity of patients with hemifacial spasm HFS and to determine the relationship of these functional changes with clinical features. Thirty patients with HFS and 33 age-, sex-, and education-matched healthy controls were included in this study. Compared with controls, HFS patients had significantly decreased ReHo values in left middle frontal gyrus (MFG), left medial cingulate cortex (MCC), left lingual gyrus, right superior temporal gyrus (STG) and right precuneus; and increased ReHo values in left precentral gyrus, anterior cingulate cortex (ACC), right brainstem, and right cerebellum. Furthermore, the mean ReHo value in brainstem showed a positive correlation with the spasm severity (r = 0.404, p = 0.027), and the mean ReHo value in MFG was inversely related with spasm severity in HFS group (r = -0.398, p = 0.028). This study reveals that HFS is associated with abnormal spontaneous brain activity in brain regions most involved in motor control and blinking movement. The disturbances of spontaneous brain activity reflected by ReHo measurements may provide insights into the neurological pathophysiology of HFS. 3).
Abnormal lateral spread response (LSR) is a typical finding in facial electromyography (EMG) in patients with hemifacial spasm (HFS). Although intraoperative monitoring of LSR has been widely used during microvascular decompression (MVD), the prognostic value of this monitoring is still debated.
As a treatment for HFS, microsurgical decompression and botulinum toxin injection have been shown to be highly successful. Anticonvulsant drugs relieve HFS in some patients; however, the use of such drugs is limited owing to their side effects, predominantly in elderly patients.
Botulinum toxin can be useful by alleviating the symptoms, but the effects are inconstant and only transient.
Although intraoperative EMG monitoring during Microvascular decompression for hemifacial spasm was beneficial for identifying the offending vessel and suggesting the most appropriate surgical end point, loss of LSR did not always correlate with long-term HFS treatment outcome. Because the HFS cure rate improved over time, revision might be considered for persistent LSR when follow-up has been performed for more than 1 year and the spasm remains despite adequate decompression 4).