Neuroplasticity of neck/craniofacial pain mechanisms: A review of basic science studies

FACIAL, HEAD AND NECK PAIN are very common complaints in Western society and are highly prevalent in chiropractic practice. The physiologic basis of the association between neck pain and headaches (if not also some forms of facial and/or jaw pain) lies in the fact that the nociceptive afferents from upper cervical and posterior cranial structures terminate in the same second-order neuron pool, termed the "medullary dorsal horn," by Gobel et al. and the "trigemino-cervical nucleus" by Bogduk. A series of experiments beginning in the mid-1980s by Sessle and his colleagues has investigated these interactions in an exploration of craniofacial pain mechanisms. This article first presents a review of current pain physiology as a background to a serial review of the relevant experiments by Sessle and his colleagues. These studies are reviewed qualitatively, in order to inform the reader about their breadth and scope. Our work has confirmed that complex patterns of sensorimotor processing underly the phenomena associated with craniofacial pain, and that various named clinical syndromes such as "upper cervical dysfunction," "greater occipital neuralgia," "cervicogenic headache," "neck-tongue syndrome," and some forms of temporomandibular joint pain may all share at least some aspects of this common mechanism. The clinical manifestations of disturbances in this mechanism are likely to include referred pain and muscular hypertonicity which are so common in myofascial pain syndromes in the craniofacial region. The astute clinician is then presented with much greater diagnostic complexity, but is also given expanded opportunities for therapeutic intervention in the challenging area of craniofacial pain.