Are Numerical Rating Scale Pain Scores Reliable for Evaluating Outcomes of Implanted Neuromodulation Therapies?

Introduction: Patient Global Impression of Change (PGIC) is an alternative to assess changes in patient symptoms following treatment in addition to Numerical Rating Scale (NRS) scores. NRS describes pain intensity and is limited in capturing fluctuations and complexities of chronic pain. PGIC is inherently comparative for overall patient-evaluated before-after change,1 and we hypothesize it may more accurately reflect changes in symptoms for patients receiving spinal cord stimulator (SCS) implants.

Methods: We performed a retrospective analysis of patients who received SCS implants in the Neuromodulation for Pain Program at Toronto Western Hospital between August 2017 and September 2024. Data on demographics, NRS (0 to 10) and PGIC levels before and after SCS implantation at 6 months to 1 year was collected. The PGIC was a 7-point ordinal scale from very much worse to very much improved.

Results: 248 patients received SCS implants in the study period (Table 1). Three patients (1%) reported being very much worse with an increase in NRS of 11%. Patients who reported no change (9%), minimally worse (6%) or much worse (9%) had reductions in NRS of 12-14%. Patients who reported minimally improved (27%), much improved (30%), and very much improved (18%) had reduction in NRS of 25%, 40% and 69% respectively (Figure 1). There was significant correlation between PGIC and percentage change in NRS in patients who reported improvement (Pearson's r -0.57, p< 0.0001) but not in those who reported worsening (Pearson's r -0.14, p=0.38).

Conclusion: It appears NRS is useful in quantifying improvement in responders but unable to capture the degree of worsening in non-responders. This suggests that pain intensity is important but not solely representative of the pain experience. Future research should examine PGIC further as the primary outcome measure of response to SCS trials and implants.