片側顔面痙攣に対するボツリヌス毒素治療

Hemifacial spasm is a disorder of the facial nerve characterized by involuntary synkinetic movement of facial muscles on the afflicted side. Causative lesions that have been reported include aneurysm of the posterior circulation, tumor, and arteriovenous malformations. However, most cases are due to the compression to the facial nerve by the aberrantly tortuous blood vessel at the base of the brain. It results in ectopic impulse generation in the facial nerve, with propagation of the impulse through ephaptic transmission, causing the involuntary synchronous motion of half the face. Botulinum toxin type A (BTX-A) is clearly the first choice for treatment of hemifacial spasm. It is relatively easy to administer and provides relief in the vast majority of patients. Typically, injections of BTX-A are given into the pretarsal portions of the orbicularis oculi, corrugator, zygomatics major, zygomatics minor, and risorius muscle. At the administration of BTX-A for orbicularis oculi muscle, intracutaneous injection is recommended for the prevention of the blepharoptosis and diplopia. Usually, 2.5-5 units of BTX-A is administrated in each site. The effect of this therapy is maximum at 4 weeks after the injection and maintains for about 3-5 months. The orbicularis oculi muscle is responsible for eyelid closure, excessive weakness of this muscle will result in incomplete eyelids closure and which in turn leads to exposure keratitis and drying of the cornea. If exposure keratitis occurs, application of ocular ointments or artificial tear solutions is recommended.