Role of the sympathetic nervous system in pain

Changes in the sympathetic nervous system associated with chronic pain have been described for well over a century. A complex relationship exists between the somatosensory and sympathetic nervous systems, with sympathetic involvement most likely to be a phenomenon rather than a cause. The mechanism of sympathetic involvement is still poorly understood and debated. The diagnostic criteria of complex regional pain syndrome (CRPS) include sympathetically-mediated changes. Sympathetic blocks can be used in the treatment of pain conditions, in conjunction with a multidisciplinary approach including the physical and psychological therapies. The evidence base remains weak for many treatments.