Hemifacial spasm (HFS) is characterized by intermittent, involuntary twitching of the muscles in one side of the face, which lasts from a few seconds to several minutes. Spasms occur spontaneously and without warning. They are often exacerbated by stress or fatigue, but can also be triggered by stimuli like sunlight, touch, chewing and talking. Spasms do not cause pain, but can cause discomfort, impaired vision due to forced eye closure, as well as social distraction and embarrassment.
The spasms usually begin with involvement of the muscles around the eye. With time, spasms usually become more severe and extend down the side of the face to include the cheek and mouth areas. In severe cases, spasms also involve the forehead and neck. With time, HFS usually progresses to involve more areas of the face on the affected side, while the severity and intensity of spasms increases.
A less common form of HFS involves the onset of spasms in the lower face. This is termed Atypical HFS, which tends to be more difficult to treat. Another form of HFS is called Post-Paralytic HFS, which may develop following facial paralysis from injury, trauma or Bell's Palsy. In Post-Paralytic HFS, voluntary facial contractions are usually accompanied by involuntary spasms elsewhere on the face, called intrafacial associated movements.
Diagnosis of typical HFS is based upon a clinical history of reported symptoms, and an otherwise normal neurological and cranio-facial examination. Magnetic Resonance Imaging (MRI) may demonstrate compression of the facial nerve by a blood vessel or tumor, although most imaging studies are reported to be normal. Electromyogram (EMG), which tests the electrical functioning of the nerve, demonstrates abnormal nerve activity characteristic of HFS, although is rarely necessary to diagnose the disease.
onset of HFS most often occurs in middle age, although less than 1%
of HFS cases develop before age 30. The annual rate of HFS increases
with advancing age, but on average, the incidence is 0.8 cases per 100,000
people each year. Women are affected almost twice as often as men. HFS
is not thought to be hereditary.
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