A novel approach to spinal cord stimulation (SCS), which involves targeting the dorsal horn dendrite—in contrast with more traditional ‘axonal’ SCS techniques—has been labelled as a “true breakthrough” in the field of pain management. That is according to Marc Russo (Hunter Pain Specialists, Newcastle, Australia), who presented data from a clinical trial assessing this new modality at the recent International Neuromodulation Society (INS) congress (21–26 May 2022, Barcelona, Spain).
Speaking to NeuroNews, Russo provided insight on the backdrop to these findings. “For 55 years—as long as I have been alive—we have been using SCS to stimulate the back of the spinal cord and activate a circuit that then interacts with the transmitting pain pathway to ultimately block or mitigate pain signals to the brain,” he said. “It works, and we have been refining it for the last 55 years, but we are slowly reaching a point of saturation whereby our gains are getting smaller and smaller each decade—and, still, chunks of patients are left in pain despite this therapy.”
Russo, who is also the current INS president, noted that these limitations around established SCS approaches led him to ask: “What if we did the opposite, in all aspects, to what we have been doing for 50-plus years?” He and a small team therefore devised a means to administer stimulation in a way that pertains directly to the pain pathway by targeting a different part of the nerve in the spinal cord. Specifically, he said, this meant stimulating the dorsal horn dendrites at the other end of the neurone to the axon, which has been the primary target of SCS therapies for several decades.
He presented the INS audience with an overview of the novel ‘Subwave’ waveform for preferential dorsal horn dendrite stimulation, detailing a stimulation frequency of 100Hz, a pulse width of 1,000 microseconds with the epidural leads in the typical midline position, and a bipole at T9/10 level.
“I treated one patient and their pain disappeared,” Russo told NeuroNews. “I treated a second and theirs disappeared as well. I treated a third and their pain decreased by 75%. I was gobsmacked—I just could not believe it!” These positive early findings led Russo and his colleagues to set up an investigator-initiated clinical trial in which 27 patients (mean age=58.4 years; 48% females) had their chronic non-specific low back pain (CNLBP) treated with Subwave. The primary endpoint of the trial was pain score on the Visual Analogue Scale (VAS).
Reporting six-month results from this trial at INS 2022, he said that mean VAS scores decreased from 72.48 at baseline to 27.37 at six weeks, 31.04 at 10 weeks, 32.37 at 14 weeks and, finally—in the 26 patients available for follow-up—21.47 at 26 weeks. In addition, Russo noted a median pain relief of 76.4% at 26 weeks, while 77% of patients were deemed ‘remitters’ (VAS ≤30) at the same timepoint. “This much pain relief transforms their lives back to some form of normality,” he added.
Further analysis revealed that 63% of patients were ‘responders’ and 37% were ‘high responders’ at six weeks post-activation of Subwave. These rates shifted to 70% and 30%, respectively, at 10 weeks, 63% and 26% at 14 weeks, and 77% and 46% at 26 weeks. Russo also relayed secondary endpoint data, including reductions in mean brief pain inventory (BPI) scores, improved quality-of-life outcomes, and positive findings as per the short form health survey (SF-36), at 26 weeks compared to baseline.
And, in addition to outlining high clinician ratings and treatment satisfaction levels across all follow-up timepoints, he concluded by reporting adverse events observed during the trial—including nine minor lead migrations and seven implantable pulse generator (IPG)-related events (all of which were resolved), as well as three major lead migrations, three pain flares and one surgery-related event.
Russo ended his INS 2022 presentation by claiming that this novel approach, stimulating dorsal horn dendrites, represents a promising treatment strategy for NLBP patients and is deliverable via any and all of the SCS systems that are currently commercially available. He also noted that he and his team opted not to patent Subwave, instead providing it as a “gift” to industry, physicians and patients alike that carries no additional cost or fresh regulatory burden. Russo went on to state that the results achieved are better than or equal to those seen in the latest clinical trials of any of the current cutting-edge techniques developed by neurostimulation companies to treat pain conditions.
“It is a true breakthrough in our field and will likely lead to new discoveries and new ways of doing things,” Russo told NeuroNews, “and it all came from a single night around a restaurant table asking some ‘what if’ questions, to which we knew no answers, but had a desire to explore in the hope of realising something better.”