This journal recently published a paper by Brill et al., entitled ‘Short and long term effects of conventional spinal cord stimulation on chronic pain and health perceptions: a longitudinal controlled trial’. In fact, spinal cord stimulation (SCS) is considered a last-option technique to manage chronic refractory neuropathic pain, initially based on the gate control theory with subsequent other documented mechanisms of action. Even though pain relief assessment is highly subjective, objective SCS effects on clinical pain were well-documented years ago using nociceptive flexion reflexes-RIII (Garcia-Larrea et al., 1989), ruling out a possible paresthesia-based placebo effect of the procedure. While short-term pain relief following SCS is well documented, the long-term clinical SCS benefits remain questionable. Moreover, patients may develop tolerance to SCS, with loss of the therapeutic effect over time (Taccola et al., 2020). These issues can be tackled using a control group as a comparison, which is somewhat unethical, and/or a sham group which is unrealistic since conventional SCS induces paresthesiae. Very few studies considered the long-term effects of SCS on a large sample of patients. While the beneficial effect of SCS at 1 year on a large sample was clearly documented (EMP3OWER study, 401 patients; Rosenberg et al., 2016), longer beneficial effects have only been reported in very small series (Kumar et al., 2008). The recently published article in the European Journal of Pain concerns a study on 167 patients candidates for SCS followed for 28 weeks post-implantation (Brill et al., 2022). The authors used the patients whose SCS initial trial failed as a comparison group for the patients permanently implanted with SCS. They found no beneficial effects for the SCS group at the last follow-up compared to either the pre-operative status or the failed trial group. The results of this study are in contrast with those of most published data about the efficacy of SCS, and the strength of this series includes the absence of sponsorship by the devices' manufacturers, the number of patients (n = 167) and the test–retest study for the outcome measures—with clear cut-off values for a clinically significant difference. Notwithstanding these merits, the findings and conclusions of the study are to be interpreted with caution, since the study, although well conducted and interesting, carries limitations the reader must take into consideration. The comparison group used in this study is not typical and can induce bias in the comparison. Patients disappointed by the failure of the “last chance therapy” can either work psychologically on themselves and develop useful coping strategies, can successfully modify their other therapeutic approaches, or use illicit drugs and/or medications to overcome their suffering. Thus, they cannot be considered as a robust comparison group like a placebo/sham group. Of note, outcome measures did not include medication intake in the two groups; reporting this parameter is extremely important since a significant difference between the two groups would be in itself an objective marker of SCS efficacy. A third and important limitation is the absence of multivariate analysis, most probably because of the sample size, in order to investigate the influence of several factors like the device's manufacturer, the aetiology of the chronic pain and also the pain duration. The question that remains unanswered is why the findings of this study are in contradiction with most previously published data in the literature. One explanation might be that some studies exclude analysis of drop-out patients, but the probability that this alone explains the results appears very low. Given the generally good methodology followed in this paper, only the possible biases mentioned above, the patient population/selection process and/or the technique itself appear as potential explanations of the observed divergences with previous literature. In any case, the results are of potential importance and should prompt the development of other studies with a high level of evidence, which take into consideration the challenges of placebo/sham in this context, in order to document the real long-term effectiveness of SCS on pain relief in chronic refractory neuropathic pain.
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Oct 21, 2024
Xuelian Li + 7
Open Access
