Mechanisms of myofascial pain.

The aim of this paper is to review available data and current hypotheses co ncerning myofascial pain syndrome pathophysiology and implications for clin ical practice. A muscular hypothesis has been proposed for episodic and chr onic tension headache as well as for myofascial syndrome and fibromyalgia. These different syndromes may be compared as, besides their frequent combin ation, 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 r eliable method for assessing pressure sensitivity in myofascial pain. Press ure pain is not specific to tension headache and can be observed in other c hronic headaches. It has not been demonstrated that the trigger points of f ibromyalgia are specific in idiopathic cases. It is difficult to find an el ectrophysiological investigation which is specific for myofascial pain. For daily practice, the clinical approach with interview and examination remai n the advisable attitude. Pathophysiological hypotheses help in better unde rstanding of referred pain by sensitization of nociceptive central pathways according to the Ruch convergence projection theory (1965), modified by Me nse in 1994. These theories do not however provide an explanation of the pr imary muscular mechanisms. Implications for myofascial pain patient managem ent is discussed.