Hemifacial spasm (HFS) is a rare neuromuscular disease characterized by irregular, involuntary muscle contractions (

spasm A spasm is a sudden involuntary contraction of a muscle, a group of muscles, or a hollow organ, such as the bladder. A spasmodic muscle contraction may be caused by many medical conditions, including dystonia. Most commonly, it is a musc ...

s) on one side (hemi-) of the face (-facial). The facial muscles are controlled by the

facial nerve The facial nerve, also known as the seventh cranial nerve, cranial nerve VII, or simply CN VII, is a cranial nerve that emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of ta ...

(seventh cranial nerve), which originates at the

brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is conti ...

and exits the skull below the ear where it separates into five main branches. This disease takes two forms: typical and atypical. In typical form, the twitching usually starts in the lower eyelid in

orbicularis oculi muscle The orbicularis oculi is a Sphincter, sphincter-like muscle in the face that closes the eyelids. It arises from the nasal part of the frontal bone, from the frontal process of the maxilla in front of the lacrimal groove, and from the anterior surf ...

. As time progresses, it spreads to the whole lid, then to the orbicularis oris muscle around the lips, and

buccinator muscle The bucinator () is a thin quadrilateral muscle occupying the interval between the maxilla and the Human mandible, mandible at the side of the face. It forms the anterior part of the cheek or the lateral wall of the oral cavity.Illustrated Anatom ...

in the

cheekbone In the human skull, the zygomatic bone (from ), also called cheekbone or malar bone, is a paired irregular bone, situated at the upper and lateral part of the face and forming part of the lateral wall and floor of the orbit (anatomy), orbit, of t ...

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 Old age is the range of ages for people nearing and surpassing life expectancy. People who are of old age are also referred to as: old people, elderly, elders, senior citizens, seniors or older adults. Old age is not a definite biological sta ...

women more frequently. Hemifacial spasm is much more common in some

Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...

n populations. It may be caused by a facial nerve injury, compression by a blood vessel, a

tumor A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

, or it may have no apparent cause. Individuals with spasm on both sides of the face are very rare.

Signs and symptoms

The first sign of hemifacial spasm is typically muscle movement in the patient's eyelid and around the eye. It can vary in intensity. The intermittent twitching of the eyelid, which can result in forced closure of the eye which gradually spreads to the muscles of the lower part of the face (Typical form- See Image). In atypical form the spasms start in the cheekbone area and spreads to the eyelid. Ultimately, all the muscles on that side are affected, nearly all the time. This sometimes causes the mouth to be pulled to the side. Experts have linked hemifacial spasm to facial nerve injury,

Bell's palsy Bell's palsy is a type of facial paralysis that results in a temporary inability to control the facial muscles on the affected side of the face. In most cases, the weakness is temporary and significantly improves over weeks. Symptoms can vary f ...

and

s. Although the most frequent cause is a blood vessel pressing on the

at the spot where it leaves the patient's brain stem, sometimes there is no known cause. When the affected individual is younger than 40, doctors suspect an underlying cause such as

multiple sclerosis Multiple sclerosis (MS) is an autoimmune disease resulting in damage to myelinthe insulating covers of nerve cellsin the brain and spinal cord. As a demyelinating disease, MS disrupts the nervous system's ability to Action potential, transmit ...

Causes

Three theories exist to explain the facial nerve dysfunction found in hemifacial spasm. The first proposed theory is ephaptic transmission, which is electrical activity crossing from one demyelinated neuron to another resulting in a false

synapse In the nervous system, a synapse is a structure that allows a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or a target effector cell. Synapses can be classified as either chemical or electrical, depending o ...

. The second theory involves abnormal activity of

axon An axon (from Greek ἄξων ''áxōn'', axis) or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences) is a long, slender cellular extensions, projection of a nerve cell, or neuron, ...

s at the facial nerve root end zone secondary to compressive damage/ demyelination. The third theory or "Kindling theory" involves increased excitability of the facial nerve nucleus due to feedback from a damaged facial nerve. It is generally accepted as compression of the facial nerve by vessels of the posterior circulation. In detail compression of the seventh cranial nerve by a dolichoectatic (a distorted, dilated, and elongated)

anterior inferior cerebellar artery The anterior inferior cerebellar artery (AICA) is one of three pairs of artery, arteries that supplies blood to the cerebellum. It arises from the basilar artery on each side at the level of the junction between the medulla oblongata and the pons ...

, or posterior inferior cerebellar artery is accepted to be the general cause of hemifacial spasm. Less than 1% of cases are caused by tumor. Hemifacial spasm is much more common in some Asian populations. Several families with hemifacial spasm have been reported, suggesting a genetic

etiology Etiology (; alternatively spelled aetiology or ætiology) is the study of causation or origination. The word is derived from the Greek word ''()'', meaning "giving a reason for" (). More completely, etiology is the study of the causes, origins ...

or predisposition in some cases. There appears to be an

autosomal dominant In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the Phenotype, effect of a different variant of the same gene on Homologous chromosome, the other copy of the chromosome. The firs ...

pattern of inheritance in these families with low penetrance, and except for a younger age at onset, the clinical features overlap with the

idiopathic An idiopathic disease is any disease with an unknown cause or mechanism of apparent spontaneous origin. For some medical conditions, one or more causes are somewhat understood, but in a certain percentage of people with the condition, the cause ...

cases. Evaluation of

single-nucleotide polymorphism In genetics and bioinformatics, a single-nucleotide polymorphism (SNP ; plural SNPs ) is a germline substitution of a single nucleotide at a specific position in the genome. Although certain definitions require the substitution to be present in a ...

s in genes related to vascular change causing compression of blood vessels did not show an association with hemifacial spasm. Clarifying the role of genetic susceptibility in hemifacial spasm may help to better understand the

pathogenesis In pathology, pathogenesis is the process by which a disease or disorder develops. It can include factors which contribute not only to the onset of the disease or disorder, but also to its progression and maintenance. The word comes . Descript ...

of this disease.

Diagnosis

There are several tests available to diagnose a case of hemifacial spasm. Diagnosis begins with a complete neurological exam, including an

electromyography Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph to produce a record called an electromyogram. An electromyo ...

(EMG: a test that measures and records electrical activity generated in muscle at rest and in response to muscle contraction),

magnetic resonance imaging Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to generate pictures of the anatomy and the physiological processes inside the body. MRI scanners use strong magnetic fields, magnetic field gradients, and ...

(MRI: a test that uses magnetic waves to make pictures of structures inside the head),

computed tomography A computed tomography scan (CT scan), formerly called computed axial tomography scan (CAT scan), is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers or ...

(CT scan: a type of x-ray that uses a computer to make pictures of structures inside the head), and

angiography Angiography or arteriography is a medical imaging technique used to visualize the inside, or lumen, of blood vessels and organs of the body, with particular interest in the arteries, veins, and the heart chambers. Modern angiography is perfo ...

(an x-ray exam of the blood vessels when they are filled with a contrast material). Studies have shown that the most effective method of hemifacial spasm screening is MRI. In one study, only 25% of the CT scans showed the abnormality in hemifacial spasm patients, whilst more than half of the MRI imaging demonstrated a vascular anomaly. MRI imaging is recommended as the initial screening procedure in the assessment of patients with hemifacial spasm.

Prevention

There is no known way to prevent hemifacial spasm.

Treatments

Mild cases of hemifacial spasm may be managed with sedation or carbamazepine (an anticonvulsant drug). Microsurgical decompression and botulinum toxin injections are the current main treatments used for hemifacial spasm.

Microvascular decompression

Microvascular decompression appears to be the most popular surgical treatment at present. Microvascular decompression relieves pressure on the facial nerve, which is the cause of most hemifacial spasm cases. Excellent to good results are reported in 80% or more cases with a 10% recurrence rate. In the present series approximately 10% had previously failed surgery. Serious complications can follow microsurgical decompressive operations, even when performed by experienced surgeons. These include cerebellar haematoma or swelling,

infarction (blood vessel of the brain stem blocked), cerebral infarction (ischemic stroke resulting from a disturbance in the blood vessels supplying blood to the brain), subdural haematoma and intracerebral infarction (blockage of blood flow to the brain). Death or permanent disability (hearing loss) can occur in 2% of patients of hemifacial spasm.

Botulinum toxin

Observational data from studies (the updated review in 2020 did not find any randomized controlled trials) indicates that

botulinum toxin Botulinum toxin, or botulinum neurotoxin (commonly called botox), is a neurotoxic protein produced by the bacterium ''Clostridium botulinum'' and related species. It prevents the release of the neurotransmitter acetylcholine from axon en ...

is safe and effective in the treatment of hemifacial spasm with success rates of between 76–100%. The injections are administered as an outpatient or office procedure. Although side effects do occur, these are never permanent. Repeated injections over the years remain highly effective. Whilst the toxin is expensive, the cost of even prolonged courses of injections compares favourably with the cost of surgery. Patients with HFS should be offered a number of treatment options. Sometimes as a temporary measure, medical treatment can be offered to patients with very mild cases or those who are reluctant to have surgery or botulinum toxin injections. In young and fit patients, microsurgical decompression and botulinum injections should be discussed as alternative procedures. In the majority of cases, and especially in the elderly and the unfit, botulinum toxin injection is the treatment of first choice. Imaging procedures should be done in all unusual cases of hemifacial spasm and when surgery is contemplated. Patients with hemifacial spasm were shown to have decreased sweating after botulinum toxin injections. This was first observed in 1993 by Khalaf Bushara and David Park in the first demonstration of nonmuscular use of BTX-A. Bushara further showed the efficacy of botulinum toxin in treating hyperhidrosis (excessive sweating). BTX-A was later approved for the treatment of excessive underarm sweating. This is technically known as severe primary axillary hyperhidrosis – excessive underarm sweating with an unknown cause which cannot be managed by topical agents (see focal hyperhidrosis).

Epidemiology

The incidence of hemifacial spasm is approximately 0.8 per 100,000 persons. Hemifacial spasm is more prevalent among females over 40 years of age. The estimated prevalence for women is 14.5 per 100,000 and 7.4 per 100,000 in men. Prevalence for hemifacial spasm increases with age, reaching 39.7 per 100,000 for those aged 70 years and older. One study divided 214 hemifacial patients based on the cause of the disease: ''primary'' hemifacial spasm, where the patients had a compression in the facial nerve at the end of the brainstem; and ''secondary'' hemifacial spasm, where the patients had peripheral facial palsy or nerve lesion due to tumors, demyelination, trauma or infection. The study found that 77% of cases were primary and 23% secondary. The study also found that the two sets of patients shared a similar age at onset, male to female ratios, and similar affected side. In another study of 2050 patients who had presented with hemifacial spasm between 1986 and 2009, only nine cases were caused by a cerebellopontine angle syndrome, an incidence of 0.44%.

History

The earliest descriptions about hemifacial spasm is by Shultze in 1875 and Gowers in 1899. The

of hemifacial spasm and location of the abnormality have been debated for more than a century. Surgical treatment for hemifacial spasm in the early 20th century included neurolysis (destruction of nerve tissue), stretching the facial nerve (seventh cranial nerve), and high-pressure irrigation of the nerve with lactate ringer's solution. The medical regimens of that time involved injection of the nerve with

ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...

, electrical stimulation, application of toxic compounds ( nitrate of silver,

zinc Zinc is a chemical element; it has symbol Zn and atomic number 30. It is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic tabl ...

arsenic Arsenic is a chemical element; it has Symbol (chemistry), symbol As and atomic number 33. It is a metalloid and one of the pnictogens, and therefore shares many properties with its group 15 neighbors phosphorus and antimony. Arsenic is not ...

, bromides) as well as medications such as Dilantin or other

anticonvulsants Anticonvulsants (also known as antiepileptic drugs, antiseizure drugs, or anti-seizure medications (ASM)) are a diverse group of pharmacological agents used in the treatment of epileptic seizures. Anticonvulsants are also used in the treatment ...

. Additional advances in understanding the etiology and improving treatments for hemifacial spasm did not occur until the mid-seventies. In 1977, 47 cases of hemifacial spasm underwent microvascular decompression of the facial nerve using the operating microscope. The results illustrated nerve-vessel conflicts (or cholesteatoma) to be located at the root exit zone of the facial nerve in all cases. The root exit zone is where the central

glial Glia, also called glial cells (gliocytes) or neuroglia, are non-neuronal cell (biology), cells in the central nervous system (the brain and the spinal cord) and in the peripheral nervous system that do not produce Action potential, electrical ...

al insulation of the nerve ends and the peripheral nerve axonal myelination begins, this is known as The Obersteiner-Redlich zone. Biopsies of the root exit zone demonstrated degeneration of axons, denuded axis cylinder and interrupted

myelin Myelin Sheath ( ) is a lipid-rich material that in most vertebrates surrounds the axons of neurons to insulate them and increase the rate at which electrical impulses (called action potentials) pass along the axon. The myelinated axon can be lik ...

. The results of the experiment strengthened the theory that

vascular Vascular can refer to: * blood vessels, the vascular system in animals * vascular tissue Vascular tissue is a complex transporting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue ...

compression of the facial nerve was the primary cause of hemifacial spasm, and proposed a specific region of the facial nerve where the effects of longstanding compression results in

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons). Nerves have historically been considered the basic units of the peripheral nervous system. A nerve provides a common pathway for the Electrochemistry, electrochemical nerv ...

dysfunction.