Effects of tizanidine administration on exteroceptive suppression of the temporalis muscle in patients with chronic tension-type headache.

The aim of this study was to clarify the changes of inhibitory interneuronal activity in patients with chronic tension-type headache with disorder of pericranial muscle after treatment, and the pharmacological mechanisms of tizanidine--an alpha 2 adrenergic agonist. The effects of tizanidine on exteroceptive suppression (ES) of the temporalis muscle were examined in eighteen patients with chronic tension-type headache with disorder of pericranial muscles, before and two weeks after the administration of tizanidine. The left mental nerve was stimulated, under the maximal voluntary contraction of the temporalis muscles. Two types of stimulation were used: weak stimulation with four times the sensory threshold, and strong stimulation with 10 times the sensory threshold. The rectified electromyographic activity was recorded from the right temporalis muscle. ES2 produced by four times the sensory threshold was lengthened after tizanidine administration. This fact suggests that tizanidine improves the inhibitory function in the central nervous system, and then relieves headache. However, ES produced by 10 times the sensory threshold did not change. This suggests that the effect of tizanidine may be relatively mild. The interneurones mediating ES2 may be modified by the alpha 2 agonist.