Combined Spinal Cord Stimulation and Peripheral Nerve Field Stimulation for the Treatment of Chronic Back and Neck Pain

Introduction

The concept of using neuromodulation for treatment of chronic axial pain (back and neck) is not new—as a matter of fact, chronic back pain was one of the earliest indications for spinal cord stimulation (SCS) when this modality was introduced into clinical practice in the 1960s ( ). SCS is a popular approach for contemporary pain management, and has been widely used for treatment of chronic complex pain conditions, including those involving the lumbar and cervical areas. However, it has become clear that axial low back and neck pain remains relatively less responsive to SCS when compared to the pain in extremities and the thoracic wall ( ). It has been reported that SCS clearly benefits many patients with chronic low back and neck pain, but it is often inadequate to achieve and maintain pain control over the long term and many patients continue to experience significant pain, requiring other treatments and interventions ( ). This may be because of difficulty in overlapping stimulation paresthesia with low back or neck pain areas; changes in pain patterns over time; migration of leads; inability to implant leads at the physiologic midline; or changes in distribution patterns of the electrical fields within the spinal canal ( ). Overall, the management of chronic low back and neck pain with SCS alone is a challenge for both physicians and patients. Multiple different concepts that involve various electrode configurations and stimulation paradigms have been introduced to address this issue ( ), but none has been universally effective.

In addition to conventional paresthesia-based SCS, various peripheral neuromodulation approaches have been used to address chronic axial pain. The most notable approach without long-term implantation is so-called percutaneous electrical nerve stimulation; it has been thoroughly investigated with large-scale studies ( ), but for a variety of reasons has not gained widespread acceptance. An alternative approach with implanted peripheral stimulators was introduced in the early 2000s and then tested in multiple clinical centers, specifically for low back pain (LBP) ( ), neck pain ( ), and other painful areas of trunk ( ). This approach has been called many different names (making literature searches very difficult), including peripheral nerve stimulation, peripheral nerve field stimulation (PNFS), subcutaneous targeted stimulation, subcutaneous targeted neuromodulation, subcutaneous peripheral nerve stimulation, subcutaneous stimulation, etc. For the purposes of this chapter, and taking into consideration multiple previous discussions on this topic ( ), we will call this approach PNFS, even though the use of the term “targeted” when describing the technique does indeed make a lot of sense ( ).

PNFS is a relatively new technique, involving placement of the leads subcutaneously over the area of the pain ( ). Successful use of PNFS has been reported for a variety of conditions, such as pain in the chest and abdominal wall, the pelvis, or even the shoulder girdle ( ). Moreover, PNFS has been reported for the treatment of axial low back and neck pain with good outcomes ( ). In most cases PNFS has been used as an “add-on” therapy when SCS alone was not sufficient for treating the back pain. Importantly, use of PNFS has opened a new approach for the management of axial back pain.

The idea of combining two different stimulation strategies is not new—it was introduced in the late 1970s when the spinal cord and the peripheral nerves were simultaneously targeted with electrical stimulation for patients with intractable leg pain ( ). Interestingly, in this study 10 out of 23 patients suffered from LBP as a part of their primary diagnosis ( ). It is not surprising, therefore, that a concept of combining SCS with PNFS in the same patient for treatment of axial LBP attracted the attention of clinicians worldwide. Currently there are multiple publications on this approach ( ); among them are anecdotal observations, case series, prospective cohorts, and even a multicenter randomized controlled trial. This chapter includes critical analysis of published studies to give the reader an overview of the current state of combined neuromodulation technique.

Combined SCS and PNFS for Low Back Pain

In the last decade or so improvements in the design of multicontact leads, implantable pulse generators (IPGs), and patient-controlled devices have enabled the development of combination therapy, including SCS/PNFS combination therapy that has become an option for the treatment of chronic back pain. Bernstein et al. reported in 2008 on the use of SCS in conjunction with PNFS for the treatment of LBP and leg pain in 20 patients who had failed conventional therapies, 14 (70%) of whom were diagnosed with failed back surgery syndrome (FBSS), 4 (20%) with degenerative disc disease, and 2 (10%) with complex regional pain syndrome ( ). In some patients the SCS/PNFS combination was used at the time of the initial trial; in others this combination was employed either at the time of permanent implant or later on, after SCS alone failed to control pain adequately. The authors found that overall pain control in the majority of patients was better with combination treatment than with either modality alone. In addition, using a combined approach provided a way of comparing the efficacy of each method at the time of trial, giving patients the opportunity to identify the best form of neuromodulation therapy for their particular pain. This preliminary data was encouraging, suggesting that the combination of SCS and PNFS may be a valuable therapeutic tool for relieving chronic lower back and radicular lower-extremity pain.

Since then more studies have investigated the effect of combined SCS and PNFS for chronic LBP. For example, Mironer et al. undertook the first prospective study in 40 patients to assess the efficacy of the interaction between SCS and PNFS and evaluate spinal–peripheral neuromodulation for axial LBP ( ). In the first part of the study, SCS and PNFS were implanted in 20 patients. Three programming options could be chosen, SCS alone, PNFS alone, or both together; 79% of the patients selected the simultaneous use of SCS and PNFS, and the overall success rate of the trials was 85%. In the second part, combination therapy was performed in another 20 patients; the programming options were SCS and PNFS separately, SCS as anode and PNFS as cathode, or the reverse. The communication between SCS and PNFS provided wider coverage of axial pain. The overall success of the trial was 90%; the program where the epidural lead served as a cathode and the PNFS lead as an anode had the highest incidence of wide axial back coverage (all but one patient). The study findings suggested that combining SCS with PNFS increased efficacy of both methods for axial back pain, and combining them achieved a much higher success rate in the same patient, although either modality alone might have been successful. This was the first study where patients had the opportunity to select the most efficient stimulation modality ( ). Interestingly, for the first time the authors studied the interaction between SCS and PNFS, and found that combining SCS and PNFS is rather effective in providing coverage for axial back pain in spinal stenosis and FBSS ( ).

Lipov studied “hybrid” neurostimulation, which is another way of saying the simultaneous use of SCS and PNFS to treat LBP and leg pain in 10 patients ( ). The author found that the mean reduction in pain intensity was 70% for back pain and 80% for leg pain in the follow-up 16 months after implantation. Interestingly, in this study two patients experienced 100% relief of both back and leg pain. The patients were noted to have over 50% reduction of pain medication use and significant functional improvement. There were no surgical complications.

Navarro et al. conducted a retrospective study to evaluate “triangular” stimulation using a combination of SCS and PNFS for the treatment of chronic pain in 40 patients ( ). One epidural electrode for SCS and two percutaneous electrodes for PNFS created a triangle, and were electrically connected through synchronized programming to produce paresthesia in the painful area. Triangular stimulation programming creates an electrical circuit by utilizing anodes in the epidural space and cathodes in each of the PNFS leads. In this study most patients were treated for LBP (>50%), with pain radiating to the lower extremities. Three patients had thoracic pain or neck pain with an upper-extremity component. The authors found that the majority of patients experienced immediate and short-term pain relief and reduction in pain medications with this combination “triangular” therapy. The improvements were maintained for some, but not all, patients at the end of a 6-month follow-up. This study demonstrated that combining SCS and PNFS therapies is, potentially, a beneficial treatment option for reducing pain levels and pain medication. Triangular stimulation in the study was very effective for treating isolated LBP because it covered larger topographic areas of the lower back than PNFS alone. The authors suggested that a feasibility study should be performed to create and document paresthesia with all programs and for triangular stimulation to become an accepted programming alternative for patients. Further studies should compare different types of combination programs, or different modes of lead placement in combination therapy, with each other.

Reverberi et al. presented another confirmatory report regarding the effect of SCS/PNFS combination therapy for the treatment of complex pain with very well-documented outcome measurements in eight patients with FBSS ( ). In this study each patient served as his/her own control; the mean numeric rating scale score was decreased from 9.5 to 4, McGill Pain Questionnaire (short form) from 16.8 to 5, Oswestry Scale score from 44.5 to 21, and Beck Depression Inventory from 28.8 to 8, while the QualityMetric’s SF-36v2 score increased from 72.8 to 108.5, as compared to the scores before treatment. The mean drug intake of opioids was decreased from 250 to 20 mg/day after an average follow-up of 1 year. The authors also showed that there was a drastic reduction in the lumbar nociceptive pain in the patients treated with the combination therapy when compared with those treated with SCS only, which also significantly improved the quality of life of the patients. The data indicated that the combination of SCS and PNFS may be a valid therapeutic strategy for FBSS because the neuropathic pain was improved by SCS and the nociceptive mixed lumbar–sacral component of the pain by PNFS. Besides, the ability to connect four leads (two intraspinal and two peripheral) added a tremendous amount of flexibility and programmability to the stimulation.

Hamm-Faber et al. did a feasibility study to evaluate subcutaneous stimulation (PNFS) as an “add-on” therapy to SCS for back pain and/or lower limb pain in 11 patients ( ). The authors found PNFS significantly reduced LBP (48%) after 12 months, based on the visual analog scale (VAS) and the Quebec Back Pain Disability Scale (QBPDS). Moreover, overall pain medication dosage was reduced by more than 70%. Their results for LBP suppression were less favorable than those published by Mironer et al., in which the overall success was 85%–90% ( ). They concluded that PNFS may be an effective “add-on” treatment for chronic LBP in patients with FBSS for whom SCS alone is insufficient in alleviating their pain. Hamm-Faber et al. also reported on a prospective study on the combined use of SCS and PNFS for LBP with a follow-up period of 4 years ( ). The findings showed PNFS significantly reduced back pain at both 12 months (VAS: 33 ± 16, P = .001) and 46 months (VAS: 40 ± 21, P = .013) as compared to baseline (VAS: 63 ± 14). The QBPDS was 61 ± 15 at baseline, 49 ± 12 at 12 months, and 53 ± 15 after 46 months, reaching statistically significant levels of P = .001 and .004, respectively. This data indicated that the combination of SCS and PNFS provides persistent long-term pain relief for leg and back pain in patients with FBSS, and can be considered an effective long-term treatment for LBP in FBSS patients.

Recently van Gorp et al. conducted the first multicenter randomized controlled trial to investigate PNFS as add-on therapy to SCS for the treatment of LBP in 52 patients with FBSS ( ). The authors found that the percentage of patients with 50% reduction of back pain was significantly higher in the PNFS add-on group (42.9%) when compared to the control group where PNFS was kept “off” (4.2%). The mean VAS score for back pain at 3 months was statistically and significantly 28.1 mm lower in the PNFS add-on group as compared to the control group. They concluded that PNFS of the low back region as an add-on therapy to SCS is effective in treating back pain in patients with FBSS where SCS alone is only effective for pain in the leg.