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Commentary

Medical interventions have not solved the epidemic of chronic low back pain: will neurostimulation of the multifidus muscle be different?

Atlas, Steven J.

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doi: 10.1097/j.pain.0000000000002259
  • Free
  • Global Year 2021

Gilligan et al. are to be commended for successfully performing and reporting the results of a randomized, sham-controlled trial of a muscle stimulation device for patients with nonneuropathic, chronic low back pain (CLBP) believed to be related to impaired multifidus function.2 The nature of the sham intervention is worth noting—all participants had the device implanted but were randomized to either fully stimulating the multifidus muscle or providing low level (sham) stimulation. At the end of the 120-day study period, those in the control group could have the device turned to full stimulation. As a result, all patients knew they were getting the intervention; only the timing of when it started was varied. This schema ensured that patients were aware they could eventually derive benefit and may have raised expectations and contributed to a greater sham benefit than anticipated.

The primary outcome, those with at least a 30% improvement in low back pain on a visual analog scale without an increase in pain meds at 120 days, showed a trend toward improvement in the intervention group (57.1% vs 46.6%), but this was not a statistically significant difference. However, secondary endpoints including change in pain and function showed differences that were more supportive of the intervention. The authors speculate about why there was a disconnect between the primary and secondary outcomes, but their reasons only highlight the need for additional studies of this neurostimulator to address these concerns.

The authors emphasize that after unblinding, all patients received the intervention and showed continued and improving benefit through 1 year. They hypothesize that the nature of the intervention, improving multifidus function by stimulation, fits with these observations. However, without blinding or comparators, one cannot say how these outcomes would compare with either a longer sham or an active treatment. As such, the data seem to support a modest short-term benefit of this device, and that improvement may increase over time out to 1 year.

Although the authors emphasized that there were few serious adverse events when using this device, it was not risk-free. Overall, 27 (13%) participants required a subsequent surgical device intervention including removal in 9%. Serious adverse events occurred in 8 participants of which 6 involved infection (3%). These complications are not trivial but seem to compare favorably with trials of spinal cord stimulation that report complications in 26% to 32%.3,4

Even if one finds these results compelling, a key question is whether others can reliably identify patients with mechanical nonneuropathic CLBP who may benefit from this device. Patients with evidence of impaired multifidus control were identified with a positive prone instability test. The reliability of this test to identify individuals who may benefit from this treatment is variable.5 If differences exist in the ability to recruit similar patients when applied in routine clinical practice, the outcomes observed may not be generalizable.

Patient eligibility included having pain on at least half of the days in the prior year that was unresponsive to at least 3 months of medical management with at least some prior physical therapy. The study excluded patients who were unemployed or receiving work-related benefits. Given that the average age of participants was 46 to 48 years, a working age population, important unanswered questions remain about whether improvements would be seen in return to work and back-related disability, given the impact of CLBP on these outcomes.7 Similarly, given the importance of back pain in the opioid epidemic, a treatment that allows patients to reduce or discontinue their use would be a major advance. Unfortunately, the protocol asked patients not to change use of pain medications during the study period. During 1-year follow-up, only a minority of patients (28%) who were on opioids at baseline were able to discontinue their use.

Finally, an intriguing aspect of this therapy is whether patients who benefit from the neurostimulator require lifelong treatment. This may relate to whether the outcomes observed are due to changes in multifidus function or are mediated through an unrelated process. There are competing hypotheses for the cause of nonneuropathic, mechanical CLBP including degenerative processes that are not believed to be reversible and thus may lead to surgical interventions. If the therapy works through a restorative mechanism of action,6 it is uncertain whether benefit may persist after stimulation is stopped and thus whether patients may not need the device long-term to manage pain and improve function.

In summary, although the results of this study may be encouraging, we should remain circumspect about the ability of a new medical intervention to address the epidemic of back-related disability.1 As such, it would be naïve to presume that this new device will be a major step forward. My hope is that future studies can elucidate whether this neurostimulator works through activation of the multifidus muscle and to better quantify the magnitude and duration of benefit in a broader range of patients. We also need to demonstrate that one can reliably identify individuals whose pain may respond to this treatment in routine practice settings. If proven to be causative through the postulated mechanism, it may ultimately encourage renewed interest in conservative interventions that can achieve similar results at an earlier stage, where prevention of disability and all the ensuing effects on quality of life, economic hardship, and increased societal costs can be positively impacted.

Conflict of interest statement

S.J. Atlas receives royalty payments as a section editor of spinal disease and back pain for UpToDate, Inc.

References

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