Hemifacial spasm is a neuromuscular disorder characterized by frequent involuntary contractions (spasms) of the muscles on one side (hemi-) of the face.

The disorder occurs in both men and women, although it more frequently affects middle-aged or elderly women.

The condition may be caused by a facial nerve injury, or a tumor, or it may have no apparent cause. Most often hemifacial spasm is caused by a blood vessel pressing on the facial nerve at the place where it exits the brainstem.

The first symptom is usually an intermittent twitching of the eyelid muscle that can lead to forced closure of the eye. The spasm may then gradually spread to involve the muscles of the lower face, which may cause the mouth to be pulled to one side. Eventually the spasms involve all of the muscles on one side of the face almost continuously. Rarely, doctors see individuals with spasm on both sides of the face.

Although normally not physically painful, hemifacial spasm may affect an individual’s self-confidence and emotional well being.

Surgical treatment in the form of microvascular decompression, which relieves pressure on the facial nerve, will relieve hemifacial spasm in many cases. Other treatments include injections of botulinum toxin into the affected areas and drug therapy with medications such as clonazepam, diazepam, and levodopa, which are used to relax the muscles.

The prognosis for an individual with hemifacial spasm depends on the treatment and their response. Some individuals will be relatively free from symptoms. Some may require additional surgery. Others may only be treatable with botulinum toxin or drugs and will have to live with a greater or lesser degree of facial spasms in their day to day life.