Myofascial trigger points: peripheral or central phenomenon?

Trigger points (TrP) are hyperirritable spots in a taut band of a skeletal muscle, which usually have referred pain. There is controversy over whether TrP are a peripheral or central nervous system phenomenon. Referred pain, the most characteristic sign of TrP, is a central phenomenon initiated and activated by peripheral sensitization, whereby the peripheral nociceptive input from the muscle can sensitize dorsal horn neurons that were previously silent. TrP are a peripheral source of nociception, and act as ongoing nociceptive stimuli contributing to pain propagation and widespread pain. Several studies support the hypothesis that TrP can induce central sensitization, and appropriate TrP treatment reduces central sensitization. In contrast, preliminary evidence suggests that central sensitization can also promote TrP activity, although further studies are needed. Proper TrP management may prevent and reverse the development of pain propagation in chronic pain conditions, because inactivation of TrP attenuates central sensitization.