(34) Investigating the Long-duration Carryover Effects of 10 kHz Spinal Cord Stimulation

Introduction: 10 kHz spinal cord stimulation (SCS) is a paresthesia-independent therapy which has a unique mechanism and therapeutic characteristics different from lower frequency strategies. One of these characteristics is a long duration ‘washout.’ In a small clinical study of different stimulation parameters, we investigated the washout duration of 10 kHz SCS.

Methods: Subjects with back pain, with or without leg pain, already using an implanted pulse generator with a single area, 10 kHz SCS stimulation program for at least 18 hours daily, for at least 14 days prior, were enrolled. After providing consent and Baseline demographic and pain scores, subjects left the clinic with their device OFF, and with instructions to leave the device OFF for over two days (58 hours), while they kept a twice-daily pain diary for numerical rating scale (NRS) of their back and leg pain intensities. Pain diaries were analyzed as follows: for each subject, the duration in hours from the start of the washout period to the first entry where the pain score was increased by 2 (t∆NRS = +2) points and 3 (t∆NRS = +3) points was estimated, either from explicit documentation in the diary, interpolation of the diary entries, or extrapolation of the diary entries beyond the 58-hour assessment period.

Results: Fifteen subjects with back pain were enrolled, 13 of whom also had leg pain. By the end of the 58-hour washout assessment period, 14 subjects reported an ∆NRS(back) ≥ +2, while 9 subjects reported a ∆NRS(back) ≥ +3. For leg pain, 10 subjects reported ∆NRS(leg) ≥ +2 and 6 subjects reported ∆NRS(leg) ≥ +3. The washout times estimated from the subject diaries are as follows.
Back Pain Leg Pain
t∆NRS = +2 29.5 ± 4.3 hours 29.4 ± 4.9 hours
t∆NRS = +3 48.6 ± 6.9 hours 52.6± 11.1 hours

Conclusion: For most subjects, after 10 kHz SCS is ceased, it took > 1 day to experience an increase in pain score > MCID [1, 2, 3]. These results are in keeping with recent literature suggesting that 10 kHz has a much longer washout period than low frequency SCS strategies, as well as providing a rationale for studies showing effective outcomes with very brief pulse dose settings [4, 5, 6]. 10 kHz SCS with long carryover effect, lasting at least 24 hours after cessation of therapy, suggests a unique, non-immediate component among its mechanisms of action. Further research is necessary to confirm these observations.