A Pilot Double-Blind Randomised Sham-Controlled Trial of Paraesthesia-Free Burst Waveform Spinal Cord Stimulation in a Small Case Series of Patients with Chronic Spinal or Limb Pain

The aim of this study was to identify methodological issues that might influence comparison of burst versus sham spinal cord stimulation for treating chronic pain. Six patients with an implanted BurstDR spinal cord stimulator were assessed double-blind during eight 3-to-4-day ON or OFF cycles over a 28-day period. The stimulator was switched off during two randomly selected cycles. Pain intensity was the primary outcome, and secondary outcomes included analgesic consumption, activity estimation and sleep quality. To minimise stimulation wash-in and wash-out effects, ratings during the first two days of each cycle, or where rescue medication was taken, were discarded. Mean ratings during ON versus OFF cycles were compared using Wilcoxon’s signed-ranks test. Pain ratings averaged 4.1 ± 2.0 during OFF cycles and 3.9 ± 2.5 during ON cycles (difference not significant). However, ratings were one or more points higher during OFF than ON cycles in two patients with recent stimulator implants who correctly identified the stimulator status during most cycles. Patients were more refreshed on waking during ON than OFF cycles but burst stimulation did not influence ratings of pain interference, mood, sensitivity to mechanical stimulation or consumption of rescue medication. The findings in our case series point to the importance of investigating individual differences in response to burst spinal cord stimulation. To establish whether this treatment is effective for managing chronic pain, selecting patients with short wash-in and wash-out times, or including lengthy periods of wash-in and wash-out in the study protocol, is crucial. Selection criteria should also include pain ratings at entry of 3 or less on a 0-10 scale; stable physical and psychological functioning with little disability; minimal rescue medication; and patients who take less than 50 morphine equivalents per day.