Myofascial Pain Syndrome

Abstract

Myofascial pain syndrome (MPS) is a form of myalgia that is characterized by local regions of muscle hardness that are tender and that cause pain to be felt at a distance, i.e., referred pain. The central component of the syndrome is the trigger point that is composed of a tender, taut band. Stimulation of the band, either mechanically or with activity, can produce pain. The active trigger point has identifiable pathophysiologic changes. The concentrations of a number of substances are measurably elevated in the milieu of the active trigger point, namely substance P, CGRP, bradykinin, and assorted cytokines, indicating that there is a chemical inflammatory response. The pH of the trigger point milieu is low, about pH 5. This is in keeping with the findings that the trigger point is hypoxic and ischemic, and therefore acidic. The trigger point has a unique electromyographic feature of persistent, low-amplitude, high frequency discharges that look like endplate potentials. The taut band conducts energy faster than the surrounding muscle tissue does because it is stiffer. The taut band can also be visualized using high definition ultrasonograpy. Clinical diagnosis of a MPS is made by history and by palpation of muscle to identify the taut band. Predisposing and perpetuating factors such as iron insufficiency, vitamin D deficiency, and chronic pelvic pain are considered and addressed if found. The goal is to eliminate the trigger points, reverse trigger point-induced weakness and incoordination, and restore normal muscle function. Manual trigger point releases, and needling the trigger point, without or with local anesthetic, and use of low-level laser are effective ways of inactivating trigger points and reducing pain. MPSs can mimic or cause many common conditions such as chronic daily headache and pelvic pain because of the pain referral patterns of the trigger points.