The Effect of Pulse Width and Contact Configuration on Paresthesia Coverage in Spinal Cord Stimulation

Objective: To investigate the effect of stimulus pulsewidth (PW) and contact configuration (CC) on the area of paresthesia (PA), perception threshold (VPT), discomfort threshold (VDT) and usage range (UR) in spinal cord stimulation (SCS). - Methods: Chronic pain patients were tested during a follow-up visit. They were stimulated monopolarly and with the CC giving each one the best analgesia. VPT, VDT and UR were determined for PW of 90, 210 and 450 µs. The paresthesia contours at VDT were drawn on a body map, digitized, PA was calculated and its anatomical composition described. The effects of PW and CC on PA, VPT, VDT and UR were tested statistically. - Results: 24 out of 31 tests with low-thoracic stimulation and 8 out of 9 tests with cervical stimulation gave a significant extension of PA at increasing PW. In 14 out of 18 tests (low-thoracic) a caudal extension was obtained (primarily in L5-S2). In cervical stimulation the extension was predominantly caudal as well. It was also shown that in contrast to VPT and VDT, UR is not significantly different when stimulating with any contact configuration. - Conclusions: PA extends caudally with increasing PW. The mechanism includes that the largest and smaller Dorsal Column (DC) fibers have a different mediolateral distribution and that smaller DC fibers have a smaller UR and can only be activated when PW is sufficiently large. A similar effect of CC on PA is unlikely as long as electrodes with a large intercontact distance are applied.