CPMT Journal

Introduction

Chronic nerve pain, including pain of peripheral nerve origin, is difficult to treat [1], and is a substantial burden for patients, who commonly experience reduced physical activity, compromised daily functioning, decreased productivity, sleep disturbances, depression, anxiety, and diminished health-related quality of life [2-11]. Only 30% to 40% of patients with chronic nerve pain achieve adequate response to conventional stepwise treatment, primarily pharmacotherapy [1]. For patients who fail to receive sufficient relief with conventional medical management, clinical guidelines now recommend interventional strategies, including neuromodulation via Peripheral Nerve Stimulation (PNS) [12,13]. A substantial clinical and real-world evidence base supports the ability of PNS to treat chronic pain of peripheral nerve origin [1418]. Similar to spinal cord stimulation (SCS) [19], PNS delivers targeted electrical impulses to modulate neural activity and reduce pain, using implanted leads and a pulse generator [20]. Recent technologic advances have enabled PNS to provide the broad, complex programming capabilities and sophisticated stimulation protocols once only available with SCS systems [17,21,22].

PNS systems are inserted using a minimally invasive procedure, with successful implantation requiring precise lead placement proximal to the target peripheral nerve, facilitated by image guidance using ultrasound and/or fluoroscopy [12]. PNS implantation under local anesthesia alone is uncommon [23], and is generally limited to the temporary placement of small devices [24]. Currently, most PNS procedures are performed with the patient awake (conscious) but sedated under Monitored Anesthesia Care (MAC), or with the patient asleep (unconscious) under general endotracheal anesthesia [23,25,26]. Confirmation of PNS-induced paraesthesia over the area of pain is typically elicited by intraoperative verbal feedback from the sedated patient during awake procedures, or by arousing patients during asleep procedures [12,27]. However, reliance on verbal patient feedback during lead implantation can be unreliable due to factors including patient stress, sedative-related confusion, impaired ability to communicate, and hearing or language difficulties [25,27-29]. Patients woken from general anesthesia may become acutely aware of pain, increasing their risk for agitation, medication-related disorientation, and impaired ability to communicate [27]. There are also safety concerns with MAC, as accidental oversedation can cause central respiratory depression, airway obstruction (due to an unprotected airway), brain damage, and death [28,30,31]. In cases of respiratory distress, the patient’s prone position during the PNS procedure can also delay resuscitation [31]. Additional risks include patient movement during the procedure [29,32], and MAC may be contraindicated in individuals with sensitivity to sedatives or local anaesthetics [27].

The use of Intraoperative Neuromonitoring (IONM) with PNS can provide continuous, objective feedback on neural function. IONM involves Electromyography (EMG), Somatosensory Evoked Potentials (SSEP), and motor-evoked potentials (MEP) to ensure accurate lead placement [25,29] while facilitating procedural safety through continuous surveillance [25,29,33]. This added layer of monitoring may support safer and more efficient procedures and improved patient comfort and satisfaction. These advantages are clinically relevant because inaccurate or incomplete patient feedback can contribute to device-related problems; for example, in a 2023 analysis of PNS from the Manufacturer and User Facility Device Experience (MAUDE) database, 8.6% of 1012 devicerelated Adverse Events (AEs) were related to reports of “unwanted stimulation” [34].

IONM has been used with SCS for over two decades, with increasing frequency [26,35,36] and with studies showing its safety and efficacy to be comparable, if not superior, to awake implantation [26,27,35,37-39]. A 2023 systematic review identified a substantial body of Level II evidence indicating superior pain relief, less extraneous paraesthesia, fewer postoperative neurologic deficits, and a 27% shorter operating time with IONM versus asleep placement for SCS [26]. To mitigate the complications of neurostimulation, the most recent evidence-based guidance from the International Neuromodulation Society (INS) recommends IONM for procedures performed under general anesthesia [25].

However, the use of IONM during PNS procedures remains underevaluated, with no published reports of IONM in PNS surgery.

In this manuscript, we report the first known case series of standardized use of IONM for permanent PNS therapy using the micro-implantable pulse generator (micro-IPG; Nalu™ Neurostimulation System [Carlsbad, CA]). The micro-IPG has shown high treatment efficacy, effectiveness, and safety across two randomized controlled clinical trials [17,40] and one large-scale real-world registry study in patients with chronic neuropathic pain [18]. The objective of this study was to demonstrate that PNS can be implanted accurately and safely under general anesthesia with IONM.

Materials and Methods

This observational, retrospective real-world study was conducted at a single, outpatient private practice pain clinic (Expert Pain, Houston, TX). All patients who initially presented with chronic peripheral neuropathic pain and numbness over the lower back and superior buttock area, had successful PNS trial procedures (i.e., achieved ≥50% pain reduction during the 7-day trial period), and were permanently implanted with PNS targeting the cluneal or lumbar medial branch nerves between April 2024 and February 2025 were included in this case series. The same surgeon (study author IS) performed all trial and permanent implantation procedures; IS is a double board-certified anaesthesiologist and interventional pain management specialist who has completed more than 2,000 implant procedures over the last 25 years.

To ensure ethical compliance and patient safety, Institutional Review Board (IRB) approval was obtained from WCG IRB, Puyallup, WA (IRB reference: 1331269), and all participants provided informed consent following standards of Good Clinical Practice [41] and Committee of Publication Ethics (COPE) guidelines [42]. The study followed IRB guidelines for data confidentiality and regulatory adherence. Data used herein were collected per usual clinical practice and stored in the patient records at the clinic. The PROCESS guidelines for case series reporting were used to draft this manuscript [43].

Permanent PNS implantation procedures were performed in accordance with the clinic’s standard of care, with patients under general endotracheal anesthesia in a prone position, utilizing fluoroscopy to guide anatomic lead placement and IONM (Cadwell Cascade Pro, Cadwell Industries, Kennewick, WA) to ensure accurate electrode placement. Anesthesia consisted of midazolam, fentanyl, and propofol for induction and a volatile agent for maintenance, typically sevoflurane. Trained and experienced technicians operated the IONM device. IONM feedback alone was used to determine if PNS coverage was appropriate; patients were not woken during the surgery. All patients were administered intraoperative antibiotics, and all incisions were closed using Vicryl and Monocryl sutures. American Society of Regional Anesthesia and Pain Medicine (ASRA) guidelines for anticoagulation were followed for any patients on antithrombotic therapy [44].

Procedures lasted approximately 1.5 hours. Afterward, patients were given detailed postoperative instructions, prescribed a 7-day course of antibiotics, and were instructed to return for evaluation 72 hours after the procedure. After sufficient site healing, all PNS devices were programmed to alternate every 3 minutes between tonic and sub-paraesthesia stimulation.

To evaluate treatment effectiveness, pain scores were obtained from patients using a standard numeric rating scale (NRS, 0 to 10) prior to the PNS trial (i.e., at baseline) and at 3 months after permanent PNS implantation. Response and high response were defined as ≥50% and ≥80% reductions in pain scores from baseline, respectively. To evaluate procedure safety, patients were evaluated immediately post-operation, before discharge, and via phone call within 24 hours. Descriptive statistics were used to calculate and summarize outcomes, including change from baseline in pain scores and response rate.

Results

A total of 30 patients received permanent PNS implantation targeting the cluneal nerve (27/30; 90.0%) or lumbar medial branch nerves (3/30; 10.0%) for chronic intractable lower back pain. Patients were a mean 76.7 years of age (range, 66-89) and 66.7% were female (Table 1). Table 2 provides detailed clinical profiles for each patient, including treatment muscle group targets. The majority (66.7%) had previous back surgery and 83.3% had previously implanted, operating SCS devices. Mean patient baseline pain score was 8.9 (range, 8-10).

Table 1: Patient Characteristics (N=30).

Table 2: Detailed Patient Profiles.