[Mechanisms of myofascial pain]

The aim of this paper is to review available data and current hypotheses concerning myofascial pain syndrome pathophysiology and implications for clinical practice. A muscular hypothesis has been proposed for episodic and chronic tension headache as well as for myofascial syndrome and fibromyalgia. These different syndromes may be compared as, besides their frequent combination, they have common features characterized by spontaneous pain, painful points, and lack of objective findings. They must be distinguished because each has its own diagnostic criteria. Pressure algometry appears to be a reliable method for assessing pressure sensitivity in myofascial pain. Pressure pain is not specific to tension headache and can be observed in other chronic headaches. It has not been demonstrated that the trigger points of fibromyalgia are specific in idiopathic cases. It is difficult to find an electrophysiological investigation which is specific for myofascial pain. For daily practice, the clinical approach with interview and examination remain the advisable attitude. Pathophysiological hypotheses help in better understanding of referred pain by sensitization of nociceptive central pathways according to the Ruch convergence projection theory (1965), modified by Mense in 1994. These theories do not however provide an explanation of the primary muscular mechanisms. Implications for myofascial pain patient management is discussed.