Pulse Width Programming in Spinal Cord Stimulation: A Clinical Study

Background: With advances in spinal cord stimulation (SCS) technology, particularly rechargeable implantable, patients are now being offered a wider range of parameters to treat their pain. In particular, pulse width (PW) programming ranges of rechargeable implantable pulse generators now match that of radiofrequency systems (with programmability up to 1000 mu s). The intent of the present study was to investigate the effects of varying PW in SCS. Objective: To understand the effects of PW programming in spinal cord stimulation (SCS). Design: Single-center, prospective, randomized, single-blind evaluation of the technical and clinical outcomes of PW programming. Setting: Acute, outpatient follow-up. Methods: Subjects using fully-implanted SCS for > 3 months to treat chronic intractable low back and/or leg pain. Programming of a wide range (50-1000 mu s) of programmed PW settings using each patient's otherwise unchanged 'walk-in' program. Outcome Measures: Paresthesia thresholds (perception, maximum comfortable, discomfort), paresthesia coverage and patient choice of tested programs. Results: We found strength-duration parameters of chronaxie and rheobase to be 295 (242 - 326) mu s and 2.5 (1.3 - 3.3) mA, respectively. The median PW of all patients' 'walk-out' programs was 400 mu s, approximately 48% higher than median chronaxie (P = 0.01), suggesting that chronaxie may not relate to patient-preferred stimulation settings. We found that 7/19 patients selected new PW programs, which significantly increased their paresthesia-pain overlap by 56% on average (P = 0.047). We estimated that 10/19 patients appeared to have greater paresthesia coverage, and 8/19 patients appeared to display a 'caudal shift' of paresthesia coverage with increased PW. Limitations: Small number of patients Conclusions: Variable PW programming in SCS appears to have clinical value, demonstrated by some patients improving their paresthesia-pain overlap, as well as the ability to increase and even 'steer' paresthesia coverage.