Hemifacial spasm is a nervous system condition in which the muscles on one side of the face twitch. The cause of hemifacial spasm is most often a blood vessel touching or pulsing against a facial nerve. A facial nerve injury or a tumor also can cause it. Sometimes there is no known cause.

Common symptoms of hemifacial spasm include jerking of muscles in the face that are most often:

• On one side of the face.
• Not controllable.
• Painless.

These muscle movements, also called contractions, often start in the eyelid. Then they might move on to the cheek and mouth on the same side of the face. At first, hemifacial spasms come and go. But over months to years, they occur almost all the time.

Sometimes, hemifacial spasms occur on both sides of the face. However, the twitching doesn't occur on both sides of the face at the same time.

A blood vessel touching a facial nerve is the most common cause of hemifacial spasm. A facial nerve injury or a tumor also can cause it. Sometimes the cause isn't known.

Hemifacial spasm sometimes starts as a result of:

• Moving the muscles in the face.
• Anxiety.
• Stress.
• Being tired.

Diagnosing hemifacial spasm might involve a physical exam. Imaging tests might find the cause of the condition.

MRI uses a magnetic field and radio waves to create detailed images of the head. This can help find the cause of hemifacial spasm. A contrast dye put into a blood vessel can show whether a blood vessel is touching the facial nerve. This is called magnetic resonance angiogram.

Diagnosing hemifacial spasm doesn't always need an MRI scan or other imaging test. Imaging tests might be for people whose symptoms aren't typical or who are having surgery.

Treatment for hemifacial spasm may include:

• Botulinum injections. A shot of botulinum toxin (Botox) into the affected muscles keeps the muscles from moving for a while. This treatment needs to be repeated every few months. It controls symptoms in most people.
• Other medicines. Some medicines, including anticonvulsant drugs, can relieve hemifacial spasm in some people.

• Surgery. There are several types of surgery that can help relieve hemifacial spasm. One type of surgery, called decompression, involves making an opening in the skull and opening the covering of the brain, called the dura. This exposes the facial nerve where it leaves the brainstem.

  A surgeon then finds the blood vessel pressing on the facial nerve. Putting a spongelike material between the nerve and blood vessel eases pressure on the nerve. This surgery often works to relieve hemifacial spasm.

  Other procedures include destroying parts of the facial nerve with surgery and heat and radio waves, called radiofrequency thermocoagulation.