Clinical outcomes and complications of peripheral nerve field stimulation in the management of refractory trigeminal pain: a systematic review and meta-analysis

OBJECTIVE

Peripheral nerve field stimulation (PNFS) is a tool in the armamentarium of treatment options for trigeminal pain. The efficacy of this modality in mitigating trigeminal pain remains unclear. The aim of this study was to examine the existing literature on PNFS and elucidate pain score outcomes associated with its use in patients with trigeminal pain.

METHODS

A systematic review and meta-analysis was performed in accordance with the PRISMA framework. The PubMed, Web of Science, and Scopus databases were queried on June 10, 2020. Studies reporting pain outcomes in more than 5 adult patients treated with PNFS for facial pain were included. The primary outcome of the study was the mean difference in the visual analog scale (VAS) score from the last follow-up to baseline, and it was analyzed by an inverse-variance, random-effect model. The risk of bias was assessed using the Newcastle-Ottawa Scale and a funnel plot.

RESULTS

Of the 4597 studies screened for inclusion, 46 relevant full-text articles were assessed for eligibility. Eleven observational cohort studies from the 46 articles were found to be eligible, and reported on a total of 109 patients. In 86% (94/109) of cases, trial stimulation was successful and followed by a permanent system implantation. VAS scores improved by 75% (mean difference 6.32/10 points, 95% CI 5.38-7.27 points) compared to baseline. Seventy-six percent (42/55) of patients became medication free or required lower doses of medications. The complication rate necessitating surgical revision was estimated at 32% per procedure.

CONCLUSIONS

These findings support the belief that PNFS provides effective, long-term pain control for trigeminal pain. Statistical heterogeneity was considerable across all studies. Future work should be aimed at conducting double-blind randomized controlled trials to determine the utility of PNFS for treating various forms of trigeminal pain for which limited therapeutic options exist.

Peripheral Nerve Field Stimulation for Chronic Back Pain: Therapy Outcome Predictive Factors

OBJECTIVE

To identify variables that influence pain reduction following peripheral nerve field stimulation (PNFS) in order to identify a potential responder profile.

METHODS

Exploratory univariate and multivariate (random forest) analyses were performed separately on 2 randomized controlled trials and a registry; all included patients with chronic back pain, mainly failed back surgery syndrome. An international expert panel judged the clinical relevance of variables to identify responders by consensus.

RESULTS

Variables identified that may help predict PNFS success in patients with back pain include patient and pain characteristics (age, time since onset of pain and spinal surgery, pain medication history, position and size of pain area, pain severity, mixed nociceptive/neuropathic pain, health-related quality of life, depression, functional disability, and leg pain status), implant procedure variables (the number and position of leads, paresthesia coverage, and amount of pain relief during the trial), and programming (number of programs, cathodes, and anodes; pulse rate; pulse width; and percentage of device usage).

CONCLUSIONS

While these analyses are exploratory and restricted to a limited sample size, they suggest variables that may play a role in predicting a therapeutic response. These results, however, are informative only and should be cautiously interpreted. Future research to validate the variables in a clinical study is needed.

Cost-Effectiveness Analysis of Peripheral Nerve Field Stimulation as Add-On Therapy to Spinal Cord Stimulation in the Treatment of Chronic Low Back Pain in Failed Back Surgery Syndrome Patients

OBJECTIVE

Presently, there is only limited evidence about the cost-effectiveness of peripheral nerve field stimulation (PNFS) and no evidence to date on the cost-effectiveness of PNFS as an add-on therapy to spinal cord stimulation (SCS). In a multicenter randomized controlled trial, PNFS as add-on therapy to SCS demonstrated clinical effectiveness in treating chronic low back pain in failed back surgery syndrome (FBSS) patients. We report here the cost-effectiveness of PNFS as additional therapy.

MATERIALS AND METHODS

Cost-effectiveness analysis was performed from a health-care perspective using the general principles of cost-utility analysis, using empirical data from our multicenter randomized controlled trial on the effectiveness of hybrid SCS + PNFS on low back pain in FBSS patients, who were back pain non-responders to initial SCS-therapy, over a time-horizon of three months. Outcome measures were costs and quality-adjusted life-years (QALYs). Cost and QALYs were integrated using the net monetary benefit (NMB). Differences in costs, effects, and NMB were analyzed using multilevel regression. Uncertainty surrounding the NMB was presented by cost-effectiveness acceptability curves.

RESULTS

A total of 52 patients implanted with both SCS and PNFS, randomly assigned to a group with PNFS either activated or inactive, completed the controlled part of the study. With mean total costs for the SCS + active PNFS group of €1813.86 (SD €109.78) versus €1103.64 (SD €123.43) for the SCS + inactive PNFS group at three months, we found an incremental cost-utility ratio of €25.311 per QALY gained and a probability being cost-effective of more than 80% given a willingness to pay for a QALY of about €40.000.

CONCLUSIONS

From a Dutch national health-care context, when the willingness to pay threshold is up to 60.000 Euros per QALY, PNFS as an add-on therapy to SCS for the treatment of low back pain in FBSS patients has a high probability of being cost-effective.

A Randomized Controlled Trial of Subcutaneous Nerve Stimulation for Back Pain Due to Failed Back Surgery Syndrome: The SubQStim Study

Objectives

To compare the effectiveness of peripheral nerve stimulation utilizing a subcutaneous lead implant technique—subcutaneous nerve stimulation (SQS) plus optimized medical management (SQS + OMM arm) vs. optimized medical management alone (OMM arm) in patients with back pain due to failed back surgery syndrome.

Patients and Methods

Patients were recruited from 21 centers, in Europe, Israel, and Australia. Eligible patients were randomized (1:1) to SQS + OMM or OMM arms. Those in the SQS arm were implanted with a neurostimulator and up to two subcutaneous percutaneous cylindrical leads in the area of pain. Patients were evaluated pre‐randomization and at one, three, six, and nine months post‐randomization. The primary endpoint was the proportion of subjects with a ≥50% reduction in back pain intensity (“responder”) from baseline to nine months. Secondary outcomes included proportion of responders with a ≥50% reduction in back pain intensity at six months and ≥30% reduction at nine months, and the mean change from baseline in back pain intensity at six and nine months between the two arms.

Results

Due to the slow rate of recruitment, the study was terminated early with 116 subjects randomized. A total of 33.9% (19/56, missing: n = 20 [36%]) of subjects in the SQS + OMM arm and 1.7% (1/60, missing: n = 24 [40%]) in the OMM arm were responders at Month 9 (p < 0.0001). Secondary objectives showed a significant difference in favor of SQS + OMM arm.

Conclusion

The results indicate that the addition of SQS to OMM is more effective than OMM alone in relieving low back pain at up to nine months.

Bilateral Peripheral Nerve Field Stimulation for Intractable Coccygeal Pain: A Case Study Using Dual Lead Intercommunication

Coccygeal pain is a difficult chronic pain problem with mixed response to various treatments. This is a report of a case of coccygeal pain that after failing various conservative and interventional procedures over five years was evaluated with a temporary peripheral sacral fascial lead followed by implantation of bilateral sacral paramedian leads for peripheral nerve field stimulation (PNFS). This resulted in marked pain control and resumption of full activity. The visual analog scale (VAS) pain score improved from eight pre-implant to one after implant and has remained at that level in follow-up. Peripheral nerve field stimulation has been reported for axial chronic back pain, post-laminectomy pain and sacroiliac joint pain either alone or in conjunction with epidural spinal cord stimulation. Both single and parallel leads have been used to provide wider stimulation but differences in location have not been examined. This is the first case report of the use of PNFS for treatment of intractable chronic coccygeal pain. The effectiveness of PNFS was established for this patient by using a prolonged 10-day temporary trial period followed by a 30-day interval without stimulation during which the pain returned to the pre-trial level before proceeding with permanent implantation, it was clear that in this case, PNFS was effective for pain control. Interestingly, the trial and permanent leads were both in the posterior sacral fascia but not in identical positions yet equally effective for pain control. The observation of the effectiveness of different positions may indicate that at least for peripheral field stimulation there may be significant current spread in the fascia. Two and three months after the implant, we examined the effect of different lead settings and the effect of unilateral stimulation compared with bilateral stimulation with and without interlead communication. The patient feedback in this case provides some understanding of the effect of field stimulation with different lead placements. A trial of a deep peripheral fascial lead for sacral and coccygeal field stimulation is a simple option and may be a reasonable approach to consider in the range of treatments for chronic coccygeal pain.

Trigemino-Cervical Neuropathic Pain Relieved by Serially Repeated Peripheral Nerve Field Stimulation Without Tolerance: Case Report

BACKGROUND

With its relative simplicity and safety, peripheral nerve field stimulation (PNFS; PENS) is contributing to the re-emergence of peripheral nerve stimulation as an effective therapy for neuropathic pain (NPP).

CASE PRESENTATION

A 70-year-old woman had developed severe, medically refractory NPP unilaterally in the scalp and face 20 years earlier, following a maxillofacial surgical procedure. PNFS gave substantial relief of the pain and allodynia and was repeated successfully on a further 25 occasions over the subsequent five years. Tolerance did not develop.

CONCLUSION

Serially repeated PNFS can provide sustained relief of NPP over long periods, without tolerance, where a permanent implant may be inappropriate, unavailable, or declined.

Intractable sacroiliac joint pain treated with peripheral nerve field stimulation

As many as 62% low back pain patients can have sacroiliac joint (SIJ) pain. There is limited (to poor) evidence in regards to long-term pain relief with therapeutic intra-articular injections and/or conventional (heat or pulsed) radiofrequency ablations (RFAs) for SIJ pain. We report our pain-clinic experience with peripheral nerve field stimulation (PNFS) for two patients of intractable SIJ pain. They had reported absence of long-term pain relief (pain relief >50% for at least 2 weeks postinjection and at least 3 months post-RFA) with SIJ injections and SIJ RFAs. Two parallel permanent 8-contact subcutaneous stimulating leads were implanted under the skin overlying their painful SIJ. Adequate stimulation in the entire painful area was confirmed. For implantable pulse generator placement, a separate subcutaneous pocket was made in the upper buttock below the iliac crest level ipsilaterally. During the pain-clinic follow-up period, the patients had reduced their pain medications requirements by half with an additional report of more than 50% improvement in their functional status. The first patient passed away 2 years after the PNFS procedure due to medical causes unrelated to his chronic pain. The second patient has been comfortable with PNFS-induced analgesic regimen during her pain-clinic follow-up during last 5 years. In summary, PNFS can be an effective last resort option for SIJ pain wherein conventional interventional pain techniques have failed, and analgesic medication requirements are escalating or causing unwarranted side-effects.

Peripheral Nerve Field Stimulation Therapy for Patients With Thoracic Pain: A Prospective Study

OBJECTIVE

Relative to the number of patients suffering chronic lumbar and cervical pain, fewer patients suffer persistent thoracic pain. Consequently there is less literature, with smaller sample sizes, reporting treatment of this cohort. Here, we assess peripheral nerve field stimulation (PNfS) as a potential treatment for chronic thoracic pain.

MATERIALS AND METHODS

This study included 20 consecutive chronic thoracic pain sufferers that responded successfully to PNfS trial. The patients were subsequently implanted with permanent eight-contact electrode linear percutaneous leads within their major area of pain. Patients were followed up at 12 months for outcome reporting. All 20 patients were considered in the statistical analysis, despite removal of three devices prior to follow up.

RESULTS

The average baseline pre-treatment Numerical Pain Rating Scale (NPRS) score was 7.75 ± 1.4. Following PNfS, the mean NPRS score was 2.25 ±2.14, reflecting a significant average improvement of 5.5 ± 3.31. Three patients were explanted prior to follow up: the first gained excellent thoracic pain relief but pain at the Implantable Pulse Generator (IPG) site could not be overcome, the second achieved excellent pain relief but the PNfS was removed due to recurrent infection and in the final instance, the intervention offered only poor relief and the device removed.

CONCLUSION

PNfS is an effective intervention for intractable disabling thoracic pain, offering sustained and worthwhile pain relief, for the overwhelming majority of the cohort. This may be especially true when considering a combined treatment approach of PNfS and analgesic use to manage remnant pain.

Muscle Activation During Peripheral Nerve Field Stimulation Occurs Due to Recruitment of Efferent Nerve Fibers, Not Direct Muscle Activation

BACKGROUND

Peripheral nerve field stimulation (PNFS) is a potential treatment for chronic low-back pain. Pain relief using PNFS is dependent on activation of non-nociceptive Aβ-fibers. However, PNFS may also activate muscles, causing twitches and discomfort. In this study, we developed a mathematical model, to investigate the activation of sensory and motor nerves, as well as direct muscle fiber activation.

METHODS

The extracellular field was estimated using a finite element model based on the geometry of CT scanned lumbar vertebrae. The electrode was modeled as being implanted to a depth of 10-15 mm. Three implant directions were modeled; horizontally, vertically, and diagonally. Both single electrode and "between-lead" stimulation between contralateral electrodes were modeled. The extracellular field was combined with models of sensory Aβ-nerves, motor neurons and muscle fibers to estimate their activation thresholds.

RESULTS

The model showed that sensory Aβ fibers could be activated with thresholds down to 0.563 V, and the lowest threshold for motor nerve activation was 7.19 V using between-lead stimulation with the cathode located closest to the nerves. All thresholds for direct muscle activation were above 500 V.

CONCLUSIONS

The results suggest that direct muscle activation does not occur during PNFS, and concomitant motor and sensory nerve fiber activation are only likely to occur when using between-lead configuration. Thus, it may be relevant to investigate the location of the innervation zone of the low-back muscles prior to electrode implantation to avoid muscle activation.