Spinal cord stimulation: stimulating questions

Spinal Cord Stimulation: Clinical Efficacy and Potential Mechanisms

Spinal cord stimulation (SCS) is a minimally invasive therapy used for the treatment of chronic neuropathic pain. SCS is a safe and effective alternative to medications such as opioids, and multiple randomized controlled studies have demonstrated efficacy for difficult-to-treat neuropathic conditions such as failed back surgery syndrome. Conventional SCS is believed mediate pain relief via activation of dorsal column Aβ fibers, resulting in variable effects on sensory and pain thresholds, and measurable alterations in higher order cortical processing. Although potentiation of inhibition, as suggested by Wall and Melzack's gate control theory, continues to be the leading explanatory model, other segmental and supraspinal mechanisms have been described. Novel, non-standard, stimulation waveforms such as high-frequency and burst have been shown in some studies to be clinically superior to conventional SCS, however their mechanisms of action remain to be determined. Additional studies are needed, both mechanistic and clinical, to better understand optimal stimulation strategies for different neuropathic conditions, improve patient selection and optimize efficacy.

Modulation of somatosensory profiles by spinal cord stimulation in primary Raynaud's syndrome

BACKGROUND AND GOAL

 Spinal cord stimulation (SCS) is an effective antinociceptive treatment for various neuropathic pain syndromes. Apart from antinociceptive action, it may modulate overall somatosensory perception. This case report targets the question of whether SCS may alter quantitative sensory testing (QST) in a patient with primary Raynaud's syndrome.

MATERIALS AND METHODS

 We report on a 44-year-old female patient with primary Raynaud's syndrome who had SCS via cervical and lumbar electrodes. QST was performed in a standardized manner assessing cold detection threshold (CDT) and warm detection threshold (WDT), cold pain threshold (CPT) and heat pain threshold (HPT), mechanical detection threshold (MDT) and mechanical pain threshold (MPT) thresholds, and vibration detection threshold (VDT) and pressure pain thresholds (PPT). We tested at the dorsum of the right/left hand of the patient with engaged and disengaged SCS. Test results were compared with a control group of 80 subjects.

RESULTS

 Without SCS, the patient showed a sensory decrease in CDT, MDT, MPT, and VDT. SCS influenced the perception of cold, warm, and tactile detection thresholds, whereby CDT, WDT, and VDT were impaired and MDT was improved.

CONCLUSION

 SCS significantly modulated the somatosensory profile in a patient with primary Raynaud's syndrome. These effects were pronounced in qualities involving Aβ, C, and A∂ nerve fibers. Further investigations may help to understand the mechanisms of action of SCS.

Effects of sub-perception threshold spinal cord stimulation in neuropathic pain: a randomized controlled double-blind crossover study

BACKGROUND

Recent studies suggest that perception of the paraesthesia elicited by spinal cord stimulation (SCS) is not necessarily required for the pain relieving effect.

OBJECTIVE

The purpose of the study was to determine the effect of sub-perception threshold SCS in patients with neuropathic pain.

METHODS

Ten patients with implanted SCS systems underwent continuous sub-threshold stimulation and no stimulation in a blinded randomized crossover design. Pain scores under these treatment modalities were compared with usual supra-threshold stimulation.

RESULTS

Sub-threshold stimulation elicited significantly lower pain relief than supra-perception threshold SCS. Mean pain scores were 3.6 [max 6.3, min 1.9, standard deviation (SD) 1.3] under supra-threshold stimulation, 5.6 (max 9.0, min 2.4, SD 1.9) under sub-threshold stimulation and 6.4 (max 10.0, min 4.0, SD 2.0) without stimulation.

CONCLUSION

Sub-threshold stimulation under otherwise conventional stimulation parameters has a measurable but not clinically sufficient effect. Thus, the pain relieving effect elicited by SCS is not necessarily linked to the perceptibility of stimulation but may instead be attributed to the intensity of the electric field.

Costs and cost-effectiveness of spinal cord stimulation (SCS) for failed back surgery syndrome: an observational study in a workers' compensation population

STUDY DESIGN

Prospective cohort study.

OBJECTIVE

We estimated the cost-effectiveness of spinal cord stimulation (SCS) among workers' compensation recipients with failed back surgery syndrome (FBSS).

SUMMARY OF BACKGROUND DATA

Randomized controlled trial (RCT) evidence suggests that SCS is more effective at 6 months than medical management for patients with FBSS. However, procedure costs are high and workers' compensation claimants often have worse outcomes than other patients.

METHODS

We enrolled 158 FBSS patients receiving workers' compensation into three treatment groups: trial SCS with or without permanent device implant (n = 51), pain clinic (PC) evaluation with or without treatment (n = 39), and usual care (UC; n = 68). The primary outcome was a composite measure of pain, disability and opioid medication use. As reported previously, 5% of SCS patients, 3% of PC patients and 10% of UC patients achieved the primary outcome at 24 months. Using cost data from administrative databases, we calculated the cost-effectiveness of SCS, adjusting for baseline covariates.

RESULTS

Mean medical cost per SCS patient over 24 months was $52,091. This was $17,291 (95% confidence intervals [CI], $4100-30,490) higher than in the PC group and $28,128 ($17,620-38,630) higher than in the UC group. Adjusting for baseline covariates, the mean total medical and productivity loss costs per patient of the SCS group were $20,074 ($3840-35,990) higher than those of the PC group and $29,358 ($16,070-43,790) higher than those of the UC group. SCS was very unlikely (<5% probability) to be the most cost-effective intervention.

CONCLUSION

In this sample of workers' compensation recipients, the high procedure cost of SCS was not counterbalanced by lower costs of subsequent care, and SCS was not cost-effective. The benefits and potential cost savings reported in RCTs may not be replicated in workers' compensation patients treated in community settings.

The effects of spinal cord stimulation in neuropathic pain are sustained: a 24-month follow-up of the prospective randomized controlled multicenter trial of the effectiveness of spinal cord stimulation

OBJECTIVE

After randomizing 100 failed back surgery syndrome patients to receive spinal cord stimulation (SCS) plus conventional medical management (CMM) or CMM alone, the results of the 6-month Prospective Randomized Controlled Multicenter Trial of the Effectiveness of Spinal Cord Stimulation (i.e., PROCESS) showed that SCS offered superior pain relief, health-related quality of life, and functional capacity. Because the rate of crossover favoring SCS beyond 6 months would bias a long-term randomized group comparison, we present all outcomes in patients who continued SCS from randomization to 24 months and, for illustrative purposes, the primary outcome (>50% leg pain relief) per randomization and final treatment.

METHODS

Patients provided data on pain, quality of life, function, pain medication use, treatment satisfaction, and employment status. Investigators documented adverse events. Data analysis included inferential comparisons and multivariate regression analyses.

RESULTS

The 42 patients continuing SCS (of 52 randomized to SCS) reported significantly improved leg pain relief (P < 0.0001), quality of life (P <or= 0.01), and functional capacity (P = 0.0002); and 13 patients (31%) required a device-related surgical revision. At 24 months, of 46 of 52 patients randomized to SCS and 41 of 48 randomized to CMM who were available, the primary outcome was achieved by 17 (37%) randomized to SCS versus 1 (2%) to CMM (P = 0.003) and by 34 (47%) of 72 patients who received SCS as final treatment versus 1 (7%) of 15 for CMM (P = 0.02).

CONCLUSION

At 24 months of SCS treatment, selected failed back surgery syndrome patients reported sustained pain relief, clinically important improvements in functional capacity and health-related quality of life, and satisfaction with treatment.