The vasodilating effect of spinal dorsal column stimulation is mediated by sympathetic nerves.

Spinal dorsal column stimulation has been used in the treatment of a patient with a painful vasospastic condition in the right arm following surgical sympathectomy on the left side. After sympathectomy the left arm became constantly dry and warm and consistently lacked skin vasomotor (laser Doppler flowmetry) responses to arousing stimuli, indicating a complete loss of sympathetic vasomotor innervation. The return of minimal sudomotor (skin resistance) responses to mental stress 2 years after sympathectomy indicated a partial reinnervation of sweat glands. Immediately after sympathectomy, the contralateral right arm became increasingly cold and cyanotic and the patient complained of chronic painful coldness and severe cold-intolerance in the right arm. Attempts to pharmacologically vasodilate the arm with felodipine did not affect the local vasoconstriction and pain. Dorsal column stimulation (associated with symmetrical paraesthesia in both arms) induced an immediate and marked (ten-fold) increase in skin blood flow in the right arm (and in the leg), whereas skin blood flow in the left arm remained unaffected. The lack of vasomotor response in the left arm was not due to maximal vasodilatation at rest, since skin blood flow in the left arm showed a normal capacity for axon reflex vasodilatation following antidromic activation of sensory afferents. The results suggest that the marked vasodilatation induced by dorsal column stimulation is mediated by sympathetic vasomotor fibres, via modulation of central neuronal circuits involved in the regulation of skin sympathetic discharge.