Myofascial Pain Syndrome: Correlation between the Irritability of Trigger Points and the Prevalence of Local Twitch Responses during Trigger Point Injection

Objective: To assess the correlation between the trigger point [TrP] irritability in the myofascial pain syndrome [MPS] and the prevalence of one or more local twitch responses [LTRs] during TrP injection. Methods: Patients with MPS, active TrPs in the trapezius muscle, and a pain intensity greater than 5 [numerical pain scale, 0 = no pain; 10 = worst pain in life] were recruited for this study. Pain intensity and pressure pain threshold [PPT] were measured before and immediately after TrP injection. Results: A total of 72 MPS patients [30 males, 42 females] participated in this study. It was found that the pain intensity was significantly reduced [P < 0.05] and the PPT was significantly increased [P < 0.05] immediately after TrP injection. Conclusions: This study supports the hypothesis that in MPS there are multiple sensitized loci nociceptors in TrP regions and that the Local Twitch Response is related to the irritability of the TrP.