The facial nerve (cranial nerve VII or 7th nerve) is responsible for controlling movement of the face. Hemifacial spasm is a syndrome of recurring facial muscle twitches and spasms that can occur when the facial nerve is irritated or compressed by a blood vessel that courses along the brainstem.
Compression of the facial nerve most often occurs directly at the level of the brainstem where it emerges into the fluid space. The nerve is located underneath the hearing and balance nerve making access particularly challenging. The blood vessel causing the compression may be small and even a vein maybe responsible.
It is postulated that the compression creates stimulation of the nerve in a reverse direction (retrograde transmission). This results in formation going backwards into the origin of the nerve (Facial nucleus). The nerve unable to process the unusual stimulation responds by firing creating uncontrolled facial twitching.
The development of the symptomatic twitching is generally predictable. It initially starts in the eye lid occurring primarily with activity and movement. Eventually the twitching marches down the face through the cheek, jaw and into the neck.
The twitching becomes uncontrolled and occurs even when the patient is trying to quietly rest the face. In more severe cases the twitching progresses to sustained facial contractures referred to as “tonus phenomena”. Tonus phenomena behaves like a “Charlie horse of the face” creating periods where the face becomes locking in place with eyes closed, cheeked contracted and jaw clenched.
In addition to being painful this can be dangerous as it creates uncontrolled loss of binocular vision by closing one eye. These situations can lead to sudden and unpredictable loss of depth perception and 3-dimensional vision.
Treatment for hemifacial spasm can also be divided into the 3 general categories discussed for trigeminal neuralgia.
- Medical therapy
Several medications have been attempted to treat hemifacial spasm with little consistent success. Most commonly these drugs fall into the general category of muscle relaxants or sedatives. Unlike trigeminal neuralgia, hemifacial spasm is rarely responsive to medication on a consistent basis.
- Ablative therapy
Botox therapy has been used to create a functional chemical block between the fine nerve endings of the facial nerve and their insertion into the muscles of the face. Botox is applied to the muscles by a series of injections. Over time Botox has a potential of reduced efficacy requiring more frequent injections to provide ongoing control. Often this will require injections at 9, 6, then 3-month intervals. The effects of Botox may potentially create facial weakness overtime.
- Microvascular decompression
Over 90% of patients benefit from significant relief of their hemifacial spasm following a microvascular decompression. The operation is well tolerated, but has associated risks. The risk of hearing loss (on the side of the operation) can range from 1-2%. Careful measures are taken during surgery to minimize these risks.