Hemifacial spasm

Hemifacial spasm (HFS) is a rare neuromuscular disease characterized by irregular, involuntary muscle contractions (spasms) on one side (hemi-) of the face (-facial). The facial muscles are controlled by the facial nerve (seventh cranial nerve), which originates at the brainstem and exits the skull below the ear where it separates into five main branches. Hemifacial spasm (HFS) is a rare neuromuscular disease characterized by irregular, involuntary muscle contractions (spasms) on one side (hemi-) of the face (-facial). The facial muscles are controlled by the facial nerve (seventh cranial nerve), which originates at the brainstem 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. 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. It may be caused by a facial nerve injury, a tumor, or it may have no apparent cause. Individuals with spasm on both sides of the face are very rare. 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 and tumors. Although the most frequent cause is a blood vessel pressing on the facial nerve 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. 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. The second theory involves abnormal activity of axons 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) vertebral 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 or predisposition in some cases. There appears to be an autosomal dominant pattern of inheritance in these families with low penetrance, and except for a younger age at onset, the clinical features overlap with the idiopathic cases.Evaluation of single-nucleotide polymorphisms 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 of this disease. There are several tests done to diagnose hemifacial spasm. Diagnosing a case of hemifacial spasm begins with a complete neurological exam, including an Electromyography (EMG – a test that measures and records electrical activity generated in muscle at rest and in response to muscle contraction), Magnetic resonance imaging (MRI – a test that uses magnetic waves to make pictures of structures inside the head), Computed tomography (CT scan – a type of x-ray that uses a computer to make pictures of structures inside the head), and Angiography (an x-ray exam of the blood vessels when they are filled with a contrast material).