Introduction

Opioid therapy in neuropathic pain patients is prevalent¹. As spinal cord stimulation (SCS) is reserved for a subset of neuropathic pain patients in which conventional medical management has failed, many patients receive opioid therapy upon referral to SCS^2,3. The aim of this study was to investigate whether preoperative opioid therapy was associated with inferior SCS outcomes defined as latest rating on Patients’ Global Impression of Change (PGIC) scale⁴ and risk of explantation.

Methods/Materials

The Neurizon Neuromodulation Database^5,6 contains detailed records of patients implanted with a permanent SCS system. From the records, we identified patients with a preoperative medicine registration as well as their latest PGIC rating and current treatment status (ongoing stimulation / explantation). Patients were divided into two groups: Opioid users and non-opioid users. Associations between opioid use and latest PGIC rating as well as treatment status were assessed by Chi-squared tests. For opioid users with known dosage, OMEs (oral morphine equivalents)⁷ were calculated in order to evaluate whether a dose-response relationship exists between preoperative opioid usage and SCS outcomes. Median OMEs of opioid users within each PGIC rating category were compared using a one-way ANOVA; for groups of treatment status an exact t-test was used.

Results

A total of 366 patients had a preoperative medicine registration: 62 % were opioid users, median opioid usage was 90 OMEs (n=207). Of the included patients, 265 had a PGIC rating with a median follow-up time of 3.0 years (IQR: 1.3-6.1). Preoperative opioid use was not associated with latest PGIC rating (p=0.37, figure 1) and median OME of opioid users within each PGIC rating category did not differ significantly (p=0.93). Opioid users were not more likely to undergo explantation of the SCS system (p=0.42, figure 2). Median OME of opioid users undergoing explantation did not differ from median OME of opioid users with ongoing stimulation (p=0.63).

Figure 1

Figure 2

Discussion

Preoperative patient selection and incomplete follow-up are sources of potential bias and should be considered when evaluating the results. Included patients differed significantly in type of pain condition, gender and age, strengthening the generalizability of our study results.

Conclusions

Compared to non-opioid users, opioid users rated similarly on their latest PGIC evaluation and were not at significantly greater risk of undergoing permanent explantation of the SCS system. For opioid users, we observed no dose-response relationship between daily opioid dose in OMEs and latest PGIC rating or risk of explantation.

References

1. Hoffman, E.M., J.C. Watson, J. St Sauver, N.P. Staff, and C.J. Klein, Association of Long-term Opioid Therapy With Functional Status, Adverse Outcomes, and Mortality Among Patients With Polyneuropathy. JAMA Neurol, 2017. 74(7): p. 773-779.

2. Kapural, L., C. Yu, M.W. Doust, B.E. Gliner, R. Vallejo, B.T. Sitzman, et al., Comparison of 10-kHz High-Frequency and Traditional Low-Frequency Spinal Cord Stimulation for the Treatment of Chronic Back and Leg Pain: 24-Month Results From a Multicenter, Randomized, Controlled Pivotal Trial. Neurosurgery, 2016. 79(5): p. 667-677.

3. Sharan, A.D., J. Riley, S. Falowski, J.E. Pope, A.T. Connolly, E. Karst, et al., Association of Opioid Usage with Spinal Cord Stimulation Outcomes. Pain Med, 2018. 19(4): p. 699-707.

4. Guy, W., ECDEU assessment manual for psychopharmacology. 1976, US Government Printing Office: Washinton DC.

5. Meier, K., L. Nikolajsen, M. Flink, R. Simonsen, I. Milidou, T.S. Jensen, et al., The Aarhus Neuromodulation Database. Neuromodulation, 2013. 16(6): p. 506-13.

6. Neurizon: Offical Web Page. 2019 [cited 2019 20-12]; Available from: http://neurizon.org/.

7. Nielsen, S., L. Degenhardt, B. Hoban, and N. Gisev, A synthesis of oral morphine equivalents (OME) for opioid utilisation studies. Pharmacoepidemiol Drug Saf, 2016. 25(6): p. 733-7.