Hemifacial spasm: when one side of the face twitches, how it differs from blepharospasm, and the treatments

When the muscles on one side of the face keep contracting without permission, usually starting around the eye, the condition may be hemifacial spasm. It is a nerve and blood vessel problem, not an eyelid problem alone, which is why it is handled differently from blepharospasm or a passing eyelid flicker. This article sets out what it is, how it differs from those two, why a scan is advised, what each treatment offers and risks, and what it means for the eye.

What is hemifacial spasm?

It is a movement disorder in which the muscles of facial expression on one side of the face contract involuntarily in sudden bursts. The muscles are supplied by the facial nerve, the seventh cranial nerve, on the same side. A 2025 review in the Journal of Neurology describes it as paroxysmal, meaning it comes in episodes, and says it can interfere with reading, driving and wellbeing.

It often begins in the eyelid region and spreads. A 2024 review describes spasms that start around the eyelid and progressively reach the forehead, cheek, the corner of the mouth, the chin and the neck muscle on that side. The main complaint can be difficulty opening the eye during daily activities, and a few people hear a typewriter-like tinnitus on the affected side. The spasms may continue during sleep, to a lesser degree, which can reduce sleep quality. It is usually one-sided; the 2025 review puts bilateral cases at 2.6%.

The same review gives a mean annual incidence of 1.53 per 100,000 people in Finland, a worldwide prevalence of about 14.5 per 100,000 in women and 7.4 in men, and onset usually between the fourth and sixth decades of life. It is uncommon, and it can resemble other facial movement disorders.

How is it different from blepharospasm and eyelid myokymia?

Hemifacial spasm affects one side of the whole face, while blepharospasm affects both eyelids together and myokymia is a small flicker in one lid. The 2024 review describes blepharospasm as increased blinking that gradually develops into bilateral, synchronous eyelid contractions, a dystonia (a movement disorder from the brain's control circuits) and not a nerve compression.

The pattern is the first clue. Spasm confined to both eyelids, with squeezing shut and trouble keeping the eyes open, points towards blepharospasm, which I explain in my article on blepharospasm in adults. A tiny, fleeting flutter in one upper or lower lid, with the rest of the face still, is the pattern of myokymia, covered in my article on eyelid twitching. Spread from the eye to the cheek and mouth on one side points to hemifacial spasm.

The distinction matters because the causes and the next steps differ. A flicker that stays in one lid is a different question. One-sided spread across the face calls for an examination by a neurologist or eye specialist and, as below, a scan.

What causes it, and why is an MRI advised?

The usual cause is an artery pressing on the facial nerve where it leaves the brainstem. The 2025 review names the anterior-inferior cerebellar artery, the posterior-inferior cerebellar artery or the vertebral artery as the vessels that interact with the nerve in the back of the skull. The contact is called neurovascular conflict.

An MRI is advised for two reasons. It looks for that contact, and it looks for other causes. The review lists vestibular schwannomas, meningiomas and arteriovenous anomalies among the structural causes to exclude, and the 2024 review adds that secondary hemifacial spasm arises from identifiable conditions such as tumour masses or multiple sclerosis. The scan most useful for the vessels uses high-resolution T2-weighted images, sometimes with an MR angiogram.

The picture is not simple. In a study of 330 people with the condition, vessel contact with the nerve was found on 97.9% of the symptomatic sides, but also on 38.8% of the sides without symptoms, and it was nerve deformity, not contact alone, that tracked closely with the spasm. The review also notes that reading these scans takes someone familiar with the facial nerve root, and that early reports can miss compression or over-call incidental contact. A scan result is therefore a matter to discuss with the neurologist or neurosurgeon who will use it.

Does it go away on its own, and what do tablets do?

Sometimes the spasm eases, but it cannot be counted on. Earlier studies suggest only 2.3 to 4.2% achieve symptom control without injections or surgery, while one more recent study of 104 people followed for about 12 years found 41.3% in remission, with little or no spasm, for an average of 6.4 years. The reports differ, and the condition is not life-limiting, so some people choose no treatment.

Tablets are used, usually for people who cannot or prefer not to have injections or surgery, but benefit is seen in a small minority. The review names antiseizure and anti-spasticity medicines, including carbamazepine, baclofen, pizotifen and clonazepam, and says evidence for many rests on isolated case reports. Several cause drowsiness, dizziness, unsteadiness and weakness, especially in older people, while gabapentin and levetiracetam may be better tolerated.

What does botulinum toxin do, and how often is it repeated?

Botulinum toxin type A, injected into the affected muscles, relaxes them, and it is the usual first treatment. The 2025 review gives an efficacy range of 73 to 98.4% and notes it is used in up to 90% of people. The effect wears off, so injections are repeated, with the review citing visits every 3 to 6 months.

The most common side effects are ptosis (a drooping upper lid) and facial weakness, which the review describes as generally mild and temporary. A Hong Kong review of 105 Asian people, 74 of them with hemifacial spasm, followed for a mean of 84 months and a mean of 19 sessions, found the dose per session in hemifacial spasm rose significantly over time, from 22.6 to 26.9 units after a mean of 18 sessions, yet the onset time, duration of effect and subjective outcome stayed similar. At least one local complication was reported by 41% of those with hemifacial spasm, with ptosis the most frequent. A 2025 meta-analysis of six studies, in 384 people with hemifacial spasm or blepharospasm, found that injecting in front of the tarsal plate (the firm plate in the lid) gave fewer cases of ptosis than the preseptal route, over the thin part of the lid above it, though it called for further trials.

The review also notes that injections need a clinician skilled in choosing the muscles and dose, and that repeat visits can be hard for people who are frail or have commitments. Droopy lids after injections are discussed in my article on droopy eyelids after botulinum toxin.

When is surgery considered, and what does it risk?

Microvascular decompression, or MVD, is an operation by a neurosurgeon that moves the artery away from the facial nerve. The 2025 review calls it the only potentially curative treatment, with significant benefit in up to 90% of those who have it, and describes a retrosigmoid craniectomy, a small opening in the skull behind the ear, to reach the nerve.

The relief can take time. The review says an effect may be delayed in up to 30% of cases, by about 30 days in most and up to a year in a few. It also reports that up to 9% of people in one series of more than 780 operations needed a second operation, and that repeat surgery is less successful and carries more complications.

One large single-centre series gives a clear published picture of the risks. It followed 1,524 people for a mean of 31 months. The result was excellent or good in 94.6%, with failure in 2.1% and recurrence in 0.4%. Complications of any kind occurred in 35.8%: facial palsy in 18.6%, hearing deficit in 7.2% and lower cranial nerve palsies in 2.8%. Most of these settled, and the permanent rates were facial weakness 1.2%, hearing deficit 2.1% and lower cranial nerve palsy 0.1%. It is a single-centre, retrospective series, and results depend on the surgical team, so these figures show the scale, not what a given unit will achieve.

Surgery tends to be discussed for people with troublesome spasm who want a lasting answer. The review notes that in certain groups only about 10% of people are referred, with a mean delay from diagnosis to surgery of up to five years. That choice is made with a neurosurgeon, weighing the risks above against a lifetime of injections.

What does it mean for the eye, driving and work?

The eye is often where the problem is first noticed, because the lid closes on its own and the view is interrupted. The reviews describe difficulty opening the eye, and the 2025 review lists reading and driving among the activities affected. Whether it is safe to drive is something to settle with the treating doctor, as the answer depends on how often and how severely the lid closes.

Treatment affects the eye too. Botulinum toxin can leave a drooping lid or a lid that does not close fully, and the 2025 meta-analysis found tearing, irritation and incomplete lid closure similar across injection techniques. If the eye feels dry, gritty or does not close properly after injections, it needs checking. The spasm itself is a good reason to see an eye specialist as well as a neurologist, and the eyelid conditions section and my hub article on why eyes look tired put it in context.