Referred pain of peripheral nerve origin: an alternative to the "myofascial pain" construct

The theory of myofascial pain syndrome (MPS) has been constructed around the trigger point (TrP), a region within a muscle from which local and remote pain can be evoked by palpation. Although their pathophysiology is obscure, TrPs have been regarded as the cause of myofascial pain. Spread and chronicity of pain are attributed to the activation of latent, secondary, and satellite TrPs. Although it lacks internal validity, this tautological concept has given rise to a system of empirical treatment that has been uncritically accepted by many. However, not only does the anatomical distribution of pain referred from TrPs bear a close relationship to the course of peripheral nerves, but the pain of MPS is also similar to nerve trunk pain, which is an example of somatic referred pain. Pain of peripheral nerve origin can be present without neurological deficit and with normal findings on conventional electrodiagnostic examination. In contrast to the theory of MPS, which considers the TrPs to be sites of primary hyperalgesia, this article argues that all MPS phenomena are better explained as secondary hyperalgesia of peripheral neural origin.