Complex regional pain syndromes - The influence of cutaneous and deep somatic sympathetic innervation on pain

Objectives: Complex regional pain syndromes (CRPS) can be relieved by sympathetic blockade. Different sympathetic efferent output channels innervate distinct effector organs (ie, cutaneous vasoconstrictor, muscle vasoconstrictor. and sudomotor neurons, as well as neurons innervating deep somatic tissues like bone, joints, and tendons). The aim of the present study was to elucidate in CRPS patients the sympathetically maintained pain (SMP) component that exclusively depends on cutaneous sympathetic activity compared with the SMP depending on the sympathetic innervation of deep somatic tissues. Methods: The sympathetic outflow to the painful skin was modulated selectively in awake humans. High and low cutaneous vasoconstrictor activity was produced in 12 CRPS type 1 patients by whole-body cooling and warming (thermal suit). Spontaneous pain was quantified during high and low cutaneous vasoconstrictor activity. By comparing the cutaneous SMP component with the change in pain that was achieved by modulation of the entire sympathetic outflow (sympathetic ganglion block), the SMP component originating in deep somatic structures was estimated. Results: The relief of spontaneous pain after sympathetic blockade was more pronounced than changes in spontaneous pain that could be induced by selective sympathetic cutaneous modulation. The entire SMP component (cutaneous and deep) changes considerably over time. It is most prominent in the acute stages of CRPS. Conclusions: Sympathetic afferent coupling takes place in the skin and in the deep somatic tissues, but especially in the acute stages of CRPS, the pain component that is influenced by the sympathetic innervation of deep somatic structures is more important than the cutaneous activation. The entire sympathetic maintained pain component is not constant in the course of the disease but decreases over time.