[Mechanisms of muscle pain : significance of trigger points and tender points]

Fibromyalgia syndrome (FMS) and myofascial pain syndrome (MPS) belong to the group of chronic non-inflammatory pain syndromes affecting muscles and tendinous insertions. Important criteria in the diagnosis of both diseases are the presence of "tender points" and "trigger points". According to ACR criteria FMS is characterized by the presence of tender points whereas trigger points are typically found in MPS.The main difference is that until now tender points could only be defined in terms of their localization, whereas trigger points can be found upon palpation which may cause a specific referred pain pattern. In addition, analysis of trigger points by microdialysis demonstrated elevated levels of pro-inflammatory substances at these sites. Moreover, local treatment of trigger points either by manipulative therapy or injection appears to be most effective for prompt relief of symptoms.