The Sympathetic Nervous System and Pain

This article reviews some of the preclinical studies of the sympathetic nervous system’s role in arthritis, inflammatory, and neuropathic pain, in light of the emerging understanding of how the immune system, sensory system, and sympathetic system markedly affect each other’s function, with many mechanisms besides sprouting. Many studies show a pro-inflammatory and pro-nociceptive role for the sympathetic nerves in preclinical models. However, these studies are sometimes conflicting, and the role of the sympathetic nerves can sometimes be anti-inflammatory or anti-nociceptive, particularly at later stages or when systemic effects on immune tissues are considered. The article discusses human correlates of these preclinical studies, as well as some possible reasons for the many conflicting studies in the literature. The article argues that sympathetic-based interventions for chronic pain conditions hold promise despite the conflicting findings in the field, especially if better ways to define appropriate subsets of patients can be developed.