Since the myofascial trigger point(MFTrP) has been described fifty years ago, its underlying pathophysiology has been remained unclear. The diagnosis also depends on the characteristic pain, tenderness and physical findings, which is very subjective. In recent years, some physicians investigated the objective findings of MFTrP, using the pressure algo meter and thermography. We investigated the electromyographic findings of MFTrP to evaluate the clinical usefulness of local twitch response(LTR) and sympathetic skin response(SSR), and to evaluate the electrophysiologic characteristics of MFTrP.

21 patients, diagnosed as myofascial trigger point syndrome on upper trapezius and so on, were evaluated for the triggering pain with visual analog scale(VAS), pressure threshold(THpr) using pressure algometer(Dolorimeter), LTR with concentric needle electrode and SSR on the palm. There was a significant negative correlation between VAS and THpr, but no significant correlation with electromyographic findings of LTR. Thus LTR could support the existence of MFTrP electrod iagnostically, but, could not explain the clinically correlated severity of MFTrP. There were only 3 patients showing abnormal SSR, who were all complaining the sympathetic symptoms on the affected arm with reffered pain. Even though referred pain to arm and hand existed, SSR was normal because suggested autonomic dysfunction of MFTrP is localized mechanism.

Among the 13 patients underwent the trigger point block, 8 patients who showed no residual LTR immediate after MFTrP block, had a great symptomatic improvement of MFTrP in a week, but 5 patients who showed the residual LTR did not. Regardless of complaint of pain and soreness immediate after block, loss of LTR would be predicted as a good treatment result.

In some cases, spontaneous EMG activity exist within the 3-4mm sized focus of MFTrP, although the taut band of MFTrP is 3-4cm length and depth. But this focus of MFTrP is a electrophysiologic changes within a muscle, not a structural changes seen by ultrasonography.