Involuntary contractions of the orbicularis oculi and other facial expression muscles are classified into eyelid-limited type, hemifacial type, and whole-face type depending on the disease pattern. The main disease entities are shown below.
Disease
Laterality
During sleep
Main features
Benign essential blepharospasm (BEB)
Bilateral
Disappears
Alleviated by photophobia, dry sensation, and sensory tricks
Intermittent involuntary closure of both eyelids of unknown cause is called benign essential blepharospasm. In normal blinking, the eyelid protractors (orbicularis oculi, corrugator supercilii, procerus) and the voluntary eyelid retractors (levator palpebrae superioris, frontalis) are simultaneously inhibited, but in patients, this simultaneous inhibition between the two muscle groups is lost.
Involuntary eyelid closure occurs due to intermittent or sustained overcontraction of the orbicularis oculi and other eyelid-closing muscles. When no other neurological or ophthalmological abnormalities are the cause, it is defined as essential.
Cases accompanied by facial involuntary movements such as lip dyskinesia are called Meige syndrome. It is considered a focal dystonia similar to blepharospasm, and dysfunction of the basal ganglia is suspected.
When limited to the eyelids, it is called essential blepharospasm; when it extends to other facial muscles, it is called Meige syndrome. Involvement of the eyelids plus the lower jaw and chin is sometimes referred to as Brueghel syndrome.
Hemifacial spasm (HFS) is a movement disorder in which involuntary tonic-clonic contractions occur in the facial muscles on one side of the face (innervated by cranial nerve VII). The ICD-10 code is G51.3.
In 1905, Joseph Babinsky first used the term “hemifacial spasm” 9). In 1947, Campbell and Keedy first described primary HFS, and in 1975, Jannetta clarified the mechanism of nerve compression by a tortuous dilated artery.
The prevalence in the United States is estimated at 8 to 15 per 100,000 people. The incidence is reported to be approximately 0.78 per 100,000 2). Women are affected about twice as often as men, and the typical age of onset is 50 to 60 years, with a higher incidence in middle-aged and older adults. The course is chronic and progressive.
Classification: It is broadly divided into primary (due to vascular compression) and secondary (due to abnormal regeneration after nerve injury or inflammation, tumors, demyelinating diseases, etc.).
Contractions occurring in a limited part of the orbicularis oculi muscle in one eye are called orbicularis oculi myokymia. Unlike essential blepharospasm, it is characterized by the absence of synchronous eyebrow depression. Contractions limited to the lower eyelid are also called eyelid tremor, and no difficulty in opening the eye is observed.
QWhat is the difference between hemifacial spasm and blepharospasm?
A
HFS is unilateral and extends to the lower face, with spasms persisting during sleep. Blepharospasm (BEB) is bilateral, centered around the orbits, accompanied by photophobia and dry eye, and resolves during sleep. Tearing on the affected side is more common in HFS, while photophobia and dryness are less common in HFS.
BEB is bilateral, with frequent blinking, often accompanied by photophobia and dry eye.
Characteristics of subjective symptoms:
Excessive blinking
Photophobia and dry eye sensation (often the reason for ophthalmology consultation)
Inability to open the eyes due to antagonism between spasms and effort to open
Aggravating factors: Worsened by bright light, fatigue, reading, etc.
Relieving factors: Improved by darkness, sleep, lying down, pressure on the brow area (sensory trick), etc.
Course: Chronic progressive with almost no spontaneous recovery. Antagonism between spasms and effort to open the eyes can lead to relaxation of surrounding tissues (e.g., brow ptosis, eyelid ptosis, skin laxity) and functional blindness due to inability to open the eyes.
In the early stage, it often begins with mild twitching of the lower eyelid. Gradually, it spreads to the entire facial muscles, including the eyelids, corners of the mouth, and the platysma. The spasms of the eyelids and the corner of the mouth occur synchronously (in the same rhythm).
Onset: Involuntary contraction of the lower eyelid.
Progression: Intermittent eyelid twitching → sustained involuntary eye closure → spread to the ipsilateral lower face and platysma.
Typical pattern: Starts from the upper and lower eyelids and spreads downward (most cases).
Atypical pattern: Starts from the orbicularis oris muscle and spreads upward (toward the eyelids).
Lacrimation: Patients often notice tearing on the affected side. Photophobia and dry eye sensation are less common (a distinguishing point from blepharospasm).
Triggers and aggravating factors: More pronounced under emotional stress. Sleep disturbances may occur due to spasms.
Persists during sleep: HFS is present during sleep (an important distinction from blepharospasm).
Pulsatile tinnitus: May occur when the tensor tympani muscle is involved.
Clinical findings (findings confirmed by physician examination)
Unilateral orbicularis oculi spasm: Synchronized with spasms of other facial muscles.
the other Babinski sign: Involuntary eyelid closure accompanied by brow elevation9).
Subtle facial muscle weakness: May be observed on the affected side.
Hearing loss: May be present.
Induction of synchronous spasms: Repetitive forced eyelid closure or lateral pulling of the mouth corner can induce synchronous spasms in the eyelid and mouth corner areas.
QDoes hemifacial spasm occur during sleep?
A
HFS is also observed during sleep. This is an important distinguishing feature from blepharospasm. Blepharospasm disappears during sleep, but HFS persists during sleep.
Essential blepharospasm of unknown cause is more common in middle-aged and older women, with onset particularly frequent in women aged 60 and older. Drug-induced (in chronic users of psychotropic drugs) and symptomatic (in schizophrenia) cases may also occur in younger individuals.
Basal ganglia dysfunction is suspected, and it is also called blepharospasm dystonia. It is thought that a lowered threshold to light stimulation leads to excessive blinking.
Differentiation of drug-induced BEB: Tardive dystonia caused by dopamine antagonists can present with symptoms similar to essential blepharospasm, so obtaining a history of medication use is important.
Definition: Caused by vascular compression of the facial nerve at the root exit zone (REZ). The most common responsible vessel is the anterior inferior cerebellar artery (AICA).
Compression site breakdown: REZ compression 94.6%, pure distal compression 0.7%, mixed compression 4.7%2).
Double compression (DC type): Both the REZ and the cerebral peduncle (CP) are compressed. This type has a higher rate of reoperation after MVD1).
Rare compression site: Compression by the labyrinthine artery within the internal auditory canal (IAC) has also been reported2).
Secondary HFS
Abnormal regeneration after nerve injury: Abnormal regeneration from Bell’s palsy, etc.
The main cause is compression of the facial nerve or pons in the posterior cranial fossa by blood vessels such as the basilar artery or AICA, and rarely by tumors or aneurysms.
Risk factors: Facial trauma, seventh cranial nerve injury, history of Bell’s palsy, arteriosclerosis, family history. Aging and hypertension promote tortuous dilation of blood vessels, increasing the risk of complication syndromes (such as coexistence with trigeminal neuralgia)5).
Provocation by the blink test is useful for diagnosis.
Rapid blink test: Sustain light, rapid blinks for 10–30 seconds and check for only strong blinks or involuntary movements/contractions of other facial muscles.
Light blink test: During voluntary blinking, check whether the eyebrow area moves or blinking itself becomes impossible.
Forceful blink test: Repeat opening after forceful eye closure and check for inability to open the eyes or strong spasmodic contractions of facial muscles.
Differentiation from dry eye: Subjective symptoms are similar, but differentiation is made by ocular findings and induction of spasms.
Exclusion of symptomatic and drug-induced causes:
Secondary blepharospasm due to extrapyramidal disorders such as Parkinson’s disease and progressive supranuclear palsy is characterized by apraxia of eyelid opening when there is no spasm.
It is necessary to exclude symptomatic blepharospasm caused by brainstem infarction or multiple sclerosis involving the basal ganglia or upper midbrain.
A detailed medication history should be taken to exclude the possibility of tardive dystonia due to dopamine antagonists.
Provocation test: Repeated forced eyelid closure or lateral pulling of the mouth corner can induce synchronous spasms in the eyelid and mouth corner areas, supporting the diagnosis.
Brainstem imaging is important to identify the cause of compression.
MRI: High-resolution imaging along the facial nerve pathway from the cerebellopontine angle (CPA), internal auditory meatus (IAM), brainstem to the skull base exit is recommended. High-resolution T2-weighted imaging can visualize vascular compression, although asymptomatic neurovascular contact may also be seen in normal individuals.
3D-CISS MRI: Can depict the neurovascular relationship in detail5).
3D-MRI fusion imaging (diffusion tensor imaging + magnetic resonance angiography): Useful for identifying the exact compression site at the REZ7).
Magnetic resonance angiography (MRA): In HFS associated with idiopathic intracranial hypertension, vascular contact may not be seen9).
Contrast-enhanced CT: An alternative when MRI cannot be performed.
AMR (abnormal muscle response) / LSR (lateral spread response): Essential for intraoperative monitoring during MVD. Disappearance of AMR can predict postoperative resolution of spasms1)2).
Subcutaneous injection of botulinum toxin type A targeting the orbicularis oculi muscle is performed. The efficacy rate is approximately 90%.
Mechanism of action: Inhibits the release of acetylcholine from nerve terminals.
Efficacy and duration:
Efficacy rate approximately 90%.
It takes a latency of 2 to 3 days for the effect to appear.
The effect lasts about 3 to 4 months. Repeated injections are necessary.
High-dose frequent treatment is often required to maintain the effect, but caution is needed as the effect may diminish over the long term.
In rare cases where blocking antibodies to type A toxin develop, type F toxin is effective but has a shorter duration.
Injection sites: Intramuscular injection near the inner and outer canthi of the upper and lower eyelids, the temporal side of the outer canthus, and the temporal one-third of the lower eyelid orbital rim. Inject with the needle tip lifted to avoid accidental injection into the levator palpebrae superioris or inferior oblique muscle.
Pharmacological treatment is based on three pharmacological hypotheses for essential blepharospasm (cholinergic excess, GABA deficiency, and dopaminergic excess). Lorazepam, clonazepam, and trihexyphenidyl (all unapproved for this indication) are used, but the effect varies greatly among individuals, with a response rate of about 15%; treatment should be left to an experienced neurologist.
Botulinum toxin type A (Botox(R) for injection) is covered by insurance in Japan for blepharospasm and hemifacial spasm. Although neurosurgery (posterior fossa microvascular decompression) is curative, botulinum toxin therapy is currently considered the first-line treatment.
Injection sites and doses: Corrugator supercilii, orbicularis oculi (evenly distributed), zygomaticus major, levator labii superioris alaeque nasi. 2.5 units each. It is important to avoid accidental injection into the levator palpebrae superioris.
Carbamazepine, clonazepam, phenytoin, gabapentin, baclofen. Efficacy is limited and side effects are significant. There is a report of response to topiramate (50 mg twice daily) in HFS associated with IIH9).
QHow long does the effect of botulinum toxin last?
A
The effect lasts about 3 to 4 months. Because nerve sprouting restores neuromuscular transmission, repeated injections are needed when the effect wears off. High-dose or frequent treatment may reduce long-term efficacy.
QWhich patients are suitable for microvascular decompression?
A
Main indications are refractory cases with poor response to botulinum toxin and younger patients. The improvement rate is about 90% with good long-term outcomes. In elderly patients without complications, results comparable to younger patients can be expected5).
6. Pathophysiology and Detailed Mechanism of Onset
Also called blepharospasm, this is a condition of excessive blinking without rhythmic blinking, and is considered an abnormality of the basal ganglia. It is inferred that excessive blinking occurs due to a lowered threshold for light stimulation.
Basal ganglia dysfunction is suspected. Blepharospasm (BEB) and hemifacial spasm (HFS) have fundamentally different mechanisms. BEB is a central (basal ganglia) problem, whereas HFS is caused by mechanical compression of the peripheral nerve (facial nerve).
The basic mechanism of primary HFS is vascular compression → demyelination → ephaptic transmission (false synaptic transmission). The electrical activity of one nerve induces activation of a neighboring nerve.
Vulnerable site of the facial nerve: The central myelin portion approximately 10 mm from the root exit point (RExP) to the transition zone (TZ) is vulnerable to vascular compression. The Obersteiner-Redlich zone (transition from central to peripheral myelin) within this portion is considered particularly vulnerable7).
Sano et al. (2022) evaluated pre- and post-MVD using 3D-MRI fusion images (DTI + MRA). They reported that the TZ of the facial nerve is approximately 0.96 mm (range 1.9–2.86 mm) and demonstrated that the AS portion of the REZ can be accurately identified7).
Mechanism of double compression (DC type): In DC-type HFS, REZ decompression may worsen compression on the CP side through a “lever principle.” Displacement of a large atherosclerotic VA pushes up the AICA, exacerbating facial nerve compression at the CP portion1).
Fujii et al. (2024) reviewed 35 cases of DC-type HFS and reported that when AMR does not disappear after REZ decompression, confirming AICA compression on the CP side and adding Teflon improves postoperative outcomes1).
IIH-related HFS: Fluctuations in cerebrospinal fluid pressure (not absolute values but the amount of change) are thought to cause hyperexcitability of the facial nerve. This is supported by the induction of HFS attacks upon standing after lumbar puncture9).
Combined HDS with trigeminal neuralgia: Occurs in about 3% of all HDS patients. Atherosclerotic vascular changes due to aging and hypertension cause elongation of blood vessels, compressing multiple adjacent nerves5).
Generally, symptoms progress during the first 5 years, but then often stabilize. In 10% of cases, the spasms resolve, while 15% become functionally blind.
High-dose and frequent treatments are often required to maintain effectiveness, but long-term efficacy may diminish, so caution is needed.
3D-MRI fusion imaging is useful for accurate depiction of the REZ, preoperative simulation, and postoperative evaluation. It can identify the AS portion of the facial nerve and visualize its positional relationship with the responsible vessel7).
The introduction of dual-branch monitoring (facial nerve temporal branch stimulation → mentalis muscle recording + marginal mandibular branch stimulation → orbicularis oculi muscle recording) has reported a 98% efficacy rate after MVD surgery 2). If AMR does not disappear, it is important to explore responsible vessels other than REZ (CP, IAC).
Guo et al. (2025) reported the first case of the labyrinthine artery compressing the facial nerve within the IAC, and showed that dual-branch monitoring could detect IAC compression that would have been missed by conventional REZ exploration 2).
Vascular compression within the IAC, previously overlooked, can cause HFS. If AMR does not disappear, systematic exploration from REZ to CP to the entire IAC is necessary2).
Pathophysiological Association Between IIH and HFS
A new pathophysiological concept has been proposed in which fluctuations in cerebrospinal fluid pressure can induce HFS. Topiramate may be effective for managing CSF pressure, and its application in the diagnosis and treatment of IIH-related HFS is attracting attention9).
Fujii K, Mori K, Tamase A, et al. Dynamic changes of abnormal muscle response during decompression procedures in double compression-type hemifacial spasm. Surg Neurol Int. 2024;15:430.
Guo Z, Zhang X, Zhao B. Hemifacial spasms caused by compression of the labyrinthine artery on the facial nerve in the internal auditory canal: a case report and review of the literature. J Med Case Rep. 2025;19:514.
Guerrero J, Huang M, Britz G. Double Crush Syndrome as a Cause of Hemifacial Spasm. Cureus. 2021;13(1):e12448.
Takaki Y, Tsutsumi S, Teramoto S, et al. Quadrigeminal cistern arachnoid cyst as a probable cause of hemifacial spasm. Radiol Case Rep. 2021;16:1300-1304.
Argie D, Lauren C, Malelak EB. A Rare Combined Trigeminal Neuralgia with Hemifacial Spasm in a 78-year-old Male Patient. Asian J Neurosurg. 2021;16:630-633.
Liu Y, Chen F, Li Z, et al. Microvascular decompression and aneurysm clipping for a patient with hemifacial spasm and ipsilateral labyrinthine artery aneurysm. CNS Neurosci Ther. 2022;28:307-309.
Sano K, Kuge A, Kondo R, et al. Ingenuity using 3D-MRI fusion image in evaluation before and after microvascular decompression for hemifacial spasm. Surg Neurol Int. 2022;13:209.
Onoda K, Sashida R, Fujiwara R, et al. Intermediate nerve neuralgia developed during hemifacial spasm follow-up: illustrative case. J Neurosurg Case Lessons. 2022;3(25):CASE22144.
Cassinelli Petersen G, Amirkhizi M, Brockmann K, Dibaj P. Hemifacial spasm through changes of cerebrospinal fluid pressure in idiopathic intracranial hypertension. Proc (Bayl Univ Med Cent). 2023;36(1):114-115.
Copy the article text and paste it into your preferred AI assistant.
Article copied to clipboard
Open an AI assistant below and paste the copied text into the chat box.
