A person who has hemifacial spasms experiences involuntary contractions on only one side of her face. These contractions occur frequently. Hemifacial spasms are a rare neuromuscular disorder: the Mayfield Clinic stated that about 8 out of every 100,000 people in the United States have this condition.
Women tend to have hemifacial spasms more often: about 15 in every 100,000 women have them, according to the University of Maryland Medical Center. The symptoms tend to start when patients are in their 40s.
Hemifacial spasms result from an abnormality with the facial nerve, the seventh cranial nerve, which relays communication from the brain to the muscles in the face. With this condition, the facial nerve sends abnormal signals to the facial muscles, resulting in the spasms. Damage to the facial nerve, such as from Bell’s palsy, injury, tumor or compression from a blood vessel, can result in the abnormal nerve signaling.
The Mayfield Clinic noted that the most common cause of hemifacial spasms is compression of the nerve by the anterior inferior cerebellar artery. In some cases, the patient’s physician may not be able to figure out the cause of the spasms.
This condition is similar to trigeminal neuralgia, another neurological condition. With trigeminal neuralgia, the fifth cranial nerve, called the trigeminal nerve, becomes affected, resulting in facial pain.
Patients with hemifacial spasms do not experience pain. Often, the first symptom is intermittent twitching of the muscle in the eyelid, according to the National Institute of Neurological Disorders and Stroke. This intermittent twitching can lead to a forced closure of the patient’s eye.
The spasms may then move down the patient’s face — this occurs for 92 percent of patients. For the other 8 percent, the symptoms of hemifacial spasms start at the chin and move up the face, noted the Mayfield Clinic.
When the spasms affect the muscles in the patient’s mouth, it can cause her mouth to be pulled to one side of her face. As time passes, a patient can have spasms that affect all of the muscles on one half of her face at the same time.