New trends in myofascial pain syndrome.

This review article summarizes recent studies on myofascial trigger point (MTrP) to further clarify the mechanism of MTrP. MTrP is the major cause of muscle pain (myofascial pain) in clinical practice. There are multiple MTrP loci in an MTrP region. An MTrP locus contains a sensory component (sensitive locus) and a motor component (active locus). A sensitive locus is the site from which pain, referred pain (ReP), and local twitch response (LTR) can be elicited by needle stimulation. Sensitive loci are probably sensitized nociceptors based on a histological study. They are widely distributed in the whole muscle, but are concentrated in the endplate zone. An active locus is the site from which spontaneous electrical activity (SEA) can be recorded. Active loci are dysfunctional endplates since SEA is essentially the same as endplate noise (EPN) recorded from an abnormal endplate as reported by neurophysiologists. Both ReP and LTRs are mediated through spinal cord mechanisms, demonstrated in both human and animal studies. The pathogenesis of MTrPs appears to be related to the integration in the spinal cord (formation of MTrP circuits) in response to the disturbance of the nerve endings and abnormal contractile mechanism at multiple dysfunctional endplates. Methods usually applied to treat MTrPs include stretch, massage, thermotherapy, electrotherapy, laser therapy, MTrP injection, dry needling, and acupuncture. The mechanism of acupuncture is similar to dry needling or MTrP injection. The new technique of MTrP injection can also be used to treat neurogenic spasticity.