February 29, 2020 | February 2020 issue
February 29, 2020 | The 36th annual American Academy of Pain Medicine convened in National Harbor, MD in late February. The event is a culmination of the multiple disciplines in clinical practice, the latest research in a patient-centered approach, and emerging methods to treat people living with chronic pain. The overwhelming sentiment at the meeting was that treatments are not singular in nature but complementary and integrative to overall pain management that includes rehabilitation, pharmacological, neuromodulation, and many alternative therapies.
Several spinal cord stimulation studies were highlighted at the meeting, including a series of studies sponsored by Boston Scientific using its Spectra WaveWriter SCS system to improve pain treatment. In a 41 subject, multi-center, observational study, the fast-acting sub-perception therapy algorithm was evaluated to improve neural targeting without paresthesia. The result was a time-efficient “sweet spot” search with real-time patient feedback resulting in an average duration of 12 minutes.
Large randomized controlled trials are the gold standard in research but not always possible; however data from the COMBO trial provides an opportunity for Level 1 evidence. The focus of this trial was to evaluate the clinical effectiveness of combined neurostimulation. In the study using the Spectra WaveWriter on 89 subjects comparing monotherapy, paresthesia-based SCS to combination therapy, results showed that there was an 88 percent higher responder rate among the combination therapy group—who also reported higher improvements in pain relief by 90 percent.
There was also a series of reports to further evaluate the data from Saluda’s recent EVOKE study comparing open-loop versus close-loop SCS. Led by Timothy Deer, one analysis evaluated the data from the double-blinded, randomized trial at the 12-month outcome period. In the closed-loop group, 56 percent of the subjects had 80 percent or more improved pain relief compared to only 37 percent in the open-loop group. Moreover, the most frequent SC activation level was six times greater among the closed-loop group.
Another team further evaluated the variability of the SC activation between the groups finding that activation variability is two times higher among the open-loop group. This high variability rate leads to more stimulation at or near threshold levels resulting in more side effects. The Avalon study, led by Marc Russo and Lawrence Poree, looked at the long-term impact of ECAP-controlled closed-loop SCS on 50 chronic pain subjects at 24 months of treatment. Participants experienced a significant reduction in programming visits from 0.52 monthly visits per patient to 0.07 visits at 24-months.
In the same timeframe, the number of patients with minimal or moderate disability increased to 74 percent within 12 months and remained at that level at 24 months. Finally, they reported sleep quality improvement scores among those with closed-loop SCS translating to 1 to 2 additional hours of sleep per night. These comparison studies are building the evidentiary case to support closed-loop SCS systems for pain treatment.
There was also caution conveyed among the pain management conference with several small case studies of adverse events associated with SCS. Two separate cases from University of Texas and Penn State reported epidural abscesses post-SCS trial implant within patients. Another unrelated study reported a case of a 70-yo male who developed gait issues and bowel and bladder incontinence post-SCS implantation. All reports stressed that these incidents can be rare but there is a need for early recognition of symptoms and education of the clinical and patient communities of potential risks.
In a session hosted by Lawrence Poree and Peter Staats, presenters suggested some means of reducing failure rates among SCS patients. There are many reasons patients report SCS failure or explantation but the top reason is loss of therapeutic effect. One factor in this may be found from a retrospective review of 165 patients who underwent SCS screening trials. Evidence suggests that the use of opioids and sedating medications could have a negative impact on SCS outcomes.
“It might be prudent for clinicians to have a conversation with their patients about why it may be important to wean them off sedative medications and opioids,” said Staats. Evidence also suggests that ECAP can allow clinicians to have real-time monitoring of spinal cord responses to stimulation and provide a new means to improve long-term effectiveness. Poree cited a lesson learned from other treatment modalities. In the cardiac pacemaker, EKG is used as a biomarker and for pharmacological agents, plasma concentration can be used as a biomarker. We understand that glial cells outnumber neurons in the spinal cord and perhaps the biomarker for SCS lies within this area.
Peripheral nerve stimulation is gaining ground on the spectrum of pain treatment. In a presentation by Vafi Salmasi of Stanford University, he made the case for ultrasound-guided PNS for post-surgical pain, offering proof of concept and feasibility study data. For instance, in a POC study stimulating the suprascapular nerve and brachial plexus on patients post ambulatory rotator cuff repair surgery, both subjects were opioid-free within 90 days. In another small study of seven subjects post ambulatory foot surgery, the average opioid use decreased to below one pill per day. Finally, in a five-subject study using the Bioness StimRouter lead on patients who underwent total knee arthroplasty, placement of the lead was at the infrapatellar branch of the saphenous nerve using ultrasound guidance. In this study, prior to stimulation the average pain intensity score was 7.8 and post stimulation it was 1.4 at six months and 1.5 at 12 months. Although the sample sizes are low, this data demonstrates that PNS may be an alternative in the treatment of post-surgical pain.
As the AAPM came to a close, two things were clear. Chronic pain is a complex but prevalent medical condition and neuromodulation is playing an expanded role in the spectrum of treatment.
