Introduction
Hemifacial Spasm is characterized by intermittent or continuous twitching of one side of the face, which usually begins around the eye and spreads over time to include the check and mouth. It is painless and involuntary and not well controlled by any oral medications.
Cause and Diagnosis
In essentially all cases, the cause is an abnormal arterial loop irritating the facial nerve (cranial nerve 7) at the point where it emanates from the brain stem. In contrast to Trigeminal Neuralgia, there is a diagnostic electrical test for hemifacial spasm. This requires an EMG (electromyogram) performed with special equipment which allows stimulation and recording of selected facial nerve branches The diagnosis of hemifacial spasm is confirmed when “lateral spread” is recorded in which stimulation of one branch of the facial nerve results in a delayed reflex contraction in muscles served by a different branch.
Although the abnormal vascular loop is difficult to visualize on MRI, an MRI scan is recommended to rule out the rare possibility of hemifacial spasm being caused by a tumor.
Treatment
Since there are no oral medications that are effective in stopping hemifacial spasm, the only options are interventional when the symptoms progress to the point of being unacceptable to the patient. The simplest option is Botulinum Toxin (Botox®) injections. This is an office procedure in which the twitching muscles are directly injected to block transmission of the abnormal signal. The disadvantage is that the improvement is usually temporary. The definitive procedure is Microvascular Decompression (MVD), which allows the surgeon to visualize the facial nerve, the brain stem and the offending vessel, and then to move the vessel and hold it away with a Teflon® pad. An EMG recording “lateral spread” should be monitored during the surgery because the lateral spread will disappear as soon as the facial nerve is decompressed, indicating a successful outcome. Because the Facial nerve is closely related to the Vestibulocochlear nerve (cranial nerve 8), auditory monitoring should be performed in the operating room as well to minimize the risk of post-operative deafness due to retraction or manipulation.