What is hemifacial spasm (HFS)?
Hemifacial spasm (HFS) is a condition characterized by painless twitching of the muscles on one side of the face. The contractions are involuntary and occur in a “tonic-clonic” fashion, meaning the facial muscles either are fully tensed or alternate quickly between being tensed and relaxed. Those with HFS experience episodes of spasms, which typically last seconds to minutes. However, certain triggers can cause these episodes to occur more often or can worsen their severity. These triggers include psychological factors (anxiety, stress, fatigue, and sleep deprivation) and physical factors (reading, chewing, specific head positions, and light exposure).
These spasms initially affect the nerves near the eye, which causes rapid eyelid closing and eyebrow raising, and expands over time to include all the face muscles. In the most severe form, HFS can cause a prolonged spasm with one eye completely shut and one half of the face fully contracted. These symptoms usually only occur on one side of the face, with only 0.5-6% of patients having HFS on both sides. Something unique about HFS, compared to most other conditions affecting muscles, is that the contractions can occur even during sleep. Over the course of years, the symptoms usually worsen. However, about 10% of patients can spontaneously recover.
Who is most affected by hemifacial spasm?
Hemifacial spasm is a fairly rare condition, with a worldwide prevalence of 9.8-11 per 100,000. Women are affected about twice as often as men are. In cases of primary HFS, symptoms usually begin between 40 to 60 years, and only 1-6% of those with HFS have symptoms before the age of 30. Researchers have not found a genetic link for HFS, meaning it does not run in families.
What causes hemifacial spasm?
The facial nerve, responsible for moving most of the muscles in the face, is affected in HFS. Most commonly, in primary HFS, a small blood vessel compresses the facial nerve at the brainstem, which is near the back of the neck. This compression irritates the nerve and causes it to malfunction. The secondary type of HFS usually occurs after a facial palsy, or when the face muscles become weak or paralyzed. Rarely, this type of HFS occurs due to other forms of compression, such as cysts, aneurysms, tumors, or arteriovenous malformations, infection, and multiple sclerosis.
How is hemifacial spasm diagnosed?
A doctor, usually a neurologist or neurosurgeon, can diagnose HFS by taking a detailed history of the patient’s symptoms. Sometimes, physicians may perform maneuvers that can trigger the repetitive facial spasms. Other tools to help diagnose hemifacial spasm are electromyography (EMG) and MRI of the brain. An EMG has a specific pattern that may indicate damage to the nerve, and an MRI scan can show if a blood vessel or other mass is compressing the facial nerve. While an MRI or EMG can help confirm the cause of HFS, these tests are not needed for a doctor to diagnose the condition.
How is hemifacial spasm treated?
Treatments for primary hemifacial spasm include oral medications, botulinum toxin injections, and surgery.
- When managing HFS, the initial treatment of choice is botulinum toxin injection, placed in the upper face, neck, and, if necessary, around the lips. This therapy works by relaxing the muscles in the face. Botulinum toxin injections are not permanent, so patients typically receive treatment every three months to help with symptoms. Several studies have shown that this treatment reduces symptoms in most patients. Although the therapy is usually effective, the need for repeat injections can be costly and inconvenient. Additionally, some patients have side effects like facial weakness, double vision, and drooping of the eyelid.
- Oral medications used to treat HFS include anticonvulsants, such as baclofen, clonazepam, carbamaxepine, and phenytoin, anticholinergics, and haloperidol. While these medications have helped some patients with the symptoms, most of these medications have not been proven to be effective and can cause severe side effects. Thus, medical therapy is not commonly used in patients with HFS.
- Surgery is an option for the minority of patients who don’t respond to botulinum toxin therapy. The procedure is called a microvascular decompression (MVD) and relieves the compression on the facial nerve by the blood vessel. The surgeon operates near the brainstem to move the blood vessel away from the nerve. A small pad is then inserted between the blood vessel and nerve. General risks of the procedure include infection, bleeding, and leaking of spinal fluid. Since MVD is performed near important brain structures, some patients may experience hearing loss, facial numbness, and facial weakness. Unlike botulinum toxin therapy, which is used to relieve symptoms for a short period of time, surgery can cure HFS in most patients.
Doctors manage patients with secondary HFS by treating the underlying cause. For example, patients that have HFS due to a large tumor may choose to undergo chemotherapy or surgery.
Author: Nivedha Kannapadi, Johns Hopkins University Medical Center
Michael Lim, Professor and Chair, Department of Neurosurgery, Stanford University School of Medicine