In a study intended to explore gender differences in patients with failed back surgery syndrome (FBSS) or chronic visceral pain, men and women have been shown to respond equally well to spinal cord stimulation and dorsal root ganglion (DRG) stimulation at follow-up—although some disparities, including “significantly lower” baseline average pain scores in male patients, were observed.
“Female gender and older age were associated with greater likelihood of having an explant compared to male gender and younger age, highlighting the potential utility of demographic information to identify patients who may encounter challenges with spinal cord stimulation,” Beatrice Bretherton (Pain Management Department, Leeds Teaching Hospitals NHS Trust, Leeds, UK) and colleagues state. “The inﬂuence of gender and age on outcomes should be further scrutinised and systematically reported in future prospective and retrospective research that measures psychosocial, biological, and clinical parameters.”
In spite of this, there were no significant differences at follow-up between men and women regarding their responses to various forms of neurostimulation for pain relief. Writing in the journal Neuromodulation: Technology at the Neural Interface, Bretherton et al add that this suggests gender may have “marginal effects” on responses to spinal cord stimulation and DRG stimulation “despite playing an inﬂuential role at baseline”.
According to the study’s authors, the ﬁndings of multiple previous investigations have indicated that pain treatments may beneﬁt one gender over the other and, as such, they assert that it is important to evaluate gender differences because they may affect a clinician’s perception of the severity of the pain condition, and, in turn, inﬂuence treatment choices. However, even with this “accumulating evidence” pointing to differences between men and women in responses to pain treatment, they note that there is limited evidence exploring gender differences in patient responses to spinal cord and DRG stimulation.
The researchers therefore investigated this phenomenon via a retrospective, single-site study undertaken on all patients with FBSS or chronic visceral pain who had received a fully implanted 10-kHz spinal cord stimulation, BurstDR (Abbott) or DRG system in the Leeds Teaching Hospitals NHS Trust between March 2012 and March 2020. They report that differences between men and women in baseline and follow-up average pain, worst pain, and quality of life (QoL) were ascertained, with the inﬂuence of gender on the occurrence and reasons for revision and explants also being assessed. The study was exploratory and not hypothesis driven.
The ﬁnal sample comprised 387 patients (211 female, 54.5%), Bretherton et al state, and men were signiﬁcantly older compared to women (mean difference=2.33 years, p=0.044) while baseline average pain was signiﬁcantly lower in men than women. Men and women responded equally well to 10-kHz spinal cord stimulation, burst spinal cord stimulation, and DRG stimulation, and there were no signiﬁcant differences between the genders in average pain, worst pain and QoL at follow-up—both before and after controlling for age. The mean follow-up duration was 24 months.
In addition to this, rates of revision were similar across the ﬁnal sample (n=60, 16%) and between the different study subgroups (FBSS=52/343, 15%; visceral pain=8/44, 18%; 10-kHz spinal cord stimulation=36/275, 13%; burst spinal cord stimulation=17/99, 17%)—the only exception being that the percentage of patients undergoing a surgical revision seemed to be higher for DRG stimulation (7/13, 54%), although Bretherton et al note that this may have been due to the smaller DRG sample size. In the ﬁnal sample, gender was “signiﬁcantly associated with lead fracture revisions”, as a greater percentage of men (n=9, 5%) had revisions due to lead fractures compared to women (n=3, 1%). Bretherton et al propose that this final distinction may have been due to differences in physical activity levels between men and women, and requires further investigation.
In total, 54 of 441 patients (12%) underwent a full-system explantation, with insufﬁcient pain relief found to be the most common reason for explant across genders in the subgroups, followed by infection and requiring a magnetic resonance imaging (MRI) scan. The authors also highlight that more women (13%) than men (6%) had an explant due to insufﬁcient pain relief. The female gender and older age were “intriguingly” associated with a greater likelihood of having an explant compared to male gender, and younger age, as well.
In their report, Bretherton et al note that they observed differences in baseline measures emerging between different spinal cord stimulation systems within each gender group. For instance, QoL was signiﬁcantly lower in females with 10-kHz spinal cord stimulation compared to those with burst spinal cord stimulation, and males with 10-kHz stimulation had signiﬁcantly higher average pain at baseline than males with BurstDR alternatives.
“Although these differences disappeared at follow-up, the proﬁles of patients undergoing 10-kHz spinal cord stimulation may be distinct from those with burst spinal cord stimulation,” Bretherton and colleagues add. “This is a key ﬁnding considering the importance of tailoring treatments to the needs of individual patients.” They also allude to several limitations of their study, including psychological variables and challenges in measuring physical activity levels, as well as the differences in biology between men and women.