[The physiopathological mechanisms behind chronic myofacial pain]

Chronic orofacial myalgia is characterized by muscle pain, tenderness, stiffness, and restricted range of mandibular movement. It can be localized and due to temporomandibular disorders, or part of a generalized myalgia, e.g. fibromyalgia. The etiology and pathophysiology are unclear, but it is reasonable to assume that both peripheral and central mechanisms take part. Peripheral sensitization by serotonin and other mediators is a possible mechanism behind the development and modulation of chronic myalgia, while amplification of pain due to central sensitization in conjunction with disordered antinociception may represent the mechanisms for the maintenance of pain. Central sensitization seems to involve wind-up phenomena due to activation of N-methyl-D-aspartate receptors located on second-order neurons in the brainstem. Derangements in descending endogenous pain modulating systems due to central serotonin deficiency may explain the disordered antinociception.