What Causes

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     Botulinum toxin (Botox®) is a purified form of the neurotoxin, which is produced by the bacteria Clostridium botulinum that causes Botulism. Small doses of Botox® may be injected into muscles, causing temporary weakness or paralysis in the injected areas. In HFS, Botox® may be injected into the affected muscles, and spasms may be blocked. The drug effect wears off after two to three months, and re-injections are then required to regain control of the spasms.

     Botox is particularly effective for HFS involving only the small muscles around the eye. Spasm control is more difficult to obtain when the larger muscles of the lower face become involved. As the severity and extent of HFS progresses over time, the effectiveness of repeated Botox® injections may diminish.

In this diagram, botulinum toxin injections are targeted
at the muscles around the eye.

     The neurotoxin Botox® is injected into affected muscles where it attaches to nerve endings. This blocks the transmission of nerve signals to the muscles, resulting in muscle weakness or paralysis. However, new nerve endings grow to replace those blocked by the Botox®, and muscle function (including spasms) returns within two to three months. Re-injections are then required repeatedly to regain control of HFS.

     Possible side effects of Botox® injections for HFS include drooping of the face, bruising, bags under the eye, and pain at the injection sites. Repeated Botox® injections may induce permanent weakness in the facial muscles. In rare instances, one may develop a resistance to the Botulinum toxin once their body has produced antibodies that render the toxin ineffective. This may occur when re-injections are performed over short intervals of time, or when high doses are used. Two types of Botox® are currently manufactured. Type A is the most common form of Botox® used, while the second form, Type B, can be tried in those who have developed a resistance to Type A.

    While Botox® has become widely used to treat patients with HFS, the spasms typically become worse over time and more difficult to control with repeated injections. Therefore, MVD surgery is considered an alternative that offers the potential to cure HFS.

      Continue to Microvascular Decompression Surgery .



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Prepared by A. M. Kaufmann, T. Lye & M. Patel
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