Mechanism of action of botulinum toxin type A in migraine prevention: a pilot study.

OBJECTIVE: The main objective of this study is to determine whether change in migraine frequency is correlated with a denervation pattern of the corrugator muscle after local botulinum toxin type A injections.

BACKGROUND: Recent studies suggest botulinum toxin type A is effective in preventing migraine. Relaxation of the corrugator muscle may be one of multiple targets of botulinum toxin type A in relieving migraine pain.

METHODS: The pretreatment amplitude of the compound muscle action potential (CMAP) was obtained in 10 patients with a migraine frequency of two to six attacks per month following stimulation of the temporal branch of the facial nerve. Patients were subsequently injected with 20 units of botulinum toxin type A at predefined sites in the procerus and corrugator muscles. CMAP was obtained on days 7, 30, 60, and 90 after injection. Migraine frequency, as reported in headache diaries, was compared with the amplitudes obtained.

RESULTS: A 50% decrease in CMAP was demonstrated in the total group by day 7. Maximal decline of CMAP was observed by day 30, and was sustained at day 60. Migraine frequency declined by 50% or more in 7 of 10 patients by day 60. Migraine response to botulinum toxin type A treatment did not correlate with the denervation pattern.

CONCLUSION: Relaxation of the corrugator muscles is not solely responsible for the pain relief in migraine patients treated with botulinum toxin type A.