1. 2017;20;E1073-E1080Loss of Efficacy to Spinal Cord Stimulator Therapy: Clinical Evidence and Possible Causes
   Retrospective Study
   Shihab U. Ahmed, MBBS, MPH, Jianren Mao, MD, PhD, Lucy Chen, MD, Yi Zhang, MD, PhD, Arissa Opalacz, BA, Sara M. Burns, MS, Sarah A. Roth, BS, Christopher M. Aiudi, PharmD, and Roger Y. Dunn, BS, MBA.

BACKGROUND: Although spinal cord stimulation (SCS) therapy has been shown to be efficacious in various pain conditions, the ability for SCS therapy to maintain long-term efficacy has been questioned.

OBJECTIVE: The purpose of this study was to investigate whether a loss of efficacy (LOE) phenomenon exists with SCS therapy and to investigate if this phenomenon is more apparent in any specific patient population.

STUDY DESIGN: A retrospective, observation chart review was conducted to evaluate the patient response to SCS therapy over time.

SETTING: Massachusetts General Hospital, Boston, Massachusetts.

METHODS: Patients who received a SCS at the Massachusetts General Hospital, between January 1, 2002 and December 31, 2012, were invited to participate. A total of 62 patients were included in this study. Various models were created to analyze pain score changes over time using 2-tailed statistical analysis. Additionally, one-way ANOVA and Pearson’s chi-square tests were used to determine if certain patient characteristics were associated with LOE.

RESULTS: Compared to the visual analog scale (VAS) score at one month after device implantation, pain scores increased 1.95 points after 2 years (95% CI: 1.06 to 2.84, P = < 0.001). There were no significant differences in baseline characteristics between the groups of patients who did and did not lose efficacy of their therapy. However, those who experienced LOE had a baseline SCS therapy VAS score 3.09 points lower than those who did not (95% CI: 1.69 to 4.48, P = < 0.001).

LIMITATIONS: This study had several limitations including the retrospective nature of its design, confounders to VAS scores, small sample size, missing data points, and the evaluation of only conventional, low-frequency SCS therapy.

CONCLUSIONS: Patients who received a SCS had a significant increase in VAS scores over time. Our data did not show any baseline patient characteristic that helped predict LOE. However, patients who have significant baseline response to therapy may be more likely to experience LOE.

KEY WORDS: Spinal cord stimulation, chronic pain, retrospective study, low frequency electrical stimulation, efficacy, chronic pain therapy