Ultrasound-Guided Peripheral Nerve Stimulator Placement in Two Soldiers with Acute Battlefield Neuropathic Pain

Abstract

Acute peripheral neuropathic pain after combat-related polytrauma is a common occurrence in the United States military that is often refractory to current drugs and regional anesthesia. Both spinal cord and peripheral nerve stimulation are successfully used for chronic neuropathic pain states, but are not reported for acute neuropathic pain. We present 2 cases of percutaneous ultrasound-guided sciatic peripheral nerve stimulation placement in soldiers who had conditions precluding them from spinal cord stimulation placement. Opioid reduction and marked increase in functionality were possible in one case, and cessation of opioid escalation, with eventual reduction after permanent implantation, was possible in the other.

In Brief

Published ahead of print February 17, 2012

Extremity trauma remains one of the most common battlefield injuries because advances in body armor have led to improved survival.^1,2 While trauma-related nociceptive pain from bone and soft tissue injuries can be severe, it is accompanied by early neuropathic pain symptoms in up to 30% to 70% of patients.^1,3 Such patients often experience an average pain score of ≥7 of 10 and worse quality of life scores.^3,4 This early polytrauma-related severe pain is suggested to be a strong risk factor for various chronic pain states.^5–7 This is evident with reported incidences of chronic extremity pain of >50%.^8,9

Early aggressive pharmacologic modalities (opioids, anticonvulsants, antidepressants, etc), physical therapy, and advanced regional anesthesia techniques are used in United States military hospitals for patients with early signs of significant neuropathic pain. Admittedly, such modalities have only theoretical benefit in trauma-related neuropathic pain states.^8,10,11 Patients who do not progress with standard interventions are considered for neuraxial neuromodulatory therapies but may not be suitable candidates because of infection, anticoagulation, or other general medical conditions.

Peripheral nerve stimulation (PNS) for neuropathic pain has a long history that is mostly described in case series involving invasive surgical implantation.^12–15 Although success rates vary, 60% to 80% of patients are reported to achieve “good” pain control.^12–15 Huntoon et al.^16–18 described a percutaneous ultrasound-guided technique and reported encouraging results in 8 patients experiencing chronic neuropathic extremity pain. However, PNS and especially percutaneous placement with ultrasound guidance has not been described in the acute setting.

We present the cases of 2 soldiers suffering from combat-related acute neuropathic pain less than 5 months from the time of injury who received ultrasound-guided peripheral nerve stimulator placement because of comorbidities that temporarily precluded them from neuraxial neuromodulation. Both patients displayed significant improvement in their pain along with decreased opioid usage and improved functionality.

CASE DESCRIPTIONS

Patient 1

A 25-year-old active duty soldier was involved in a rocket-propelled grenade attack during which he sustained numerous bilateral lower extremity soft tissue injuries. Subsequently, this patient had frequent debridement procedures with wound vacuum changes during his hospital course.

As is standard practice at our institution, pain assessments were conducted using the Defense and Veterans Pain Rating Scale (DVPRS) that has 1 component in which visual and descriptive modes are matched with a numerical scale (0: No pain − 10: As bad is could be, nothing else matters). The second component consists of a 4-question survey with questions addressing sleep, mood, activity, and level of stress (0: Does not interfere − 10: Completely interferes).

Initially, the patient reported only mild burning sensations in his left foot that were controlled with gabapentin and nortriptyline. After the cessation of surgical interventions, this pain increased to become a severe circumferential burning sensation around his foot. On examination, he had notable motor and sensory deficits in a tibial and common peroneal distribution. He was subsequently trialed on pregabalin, memantine, duloxetine, a transcutaneous electrical neural stimulation unit, Lidoderm patches, ketamine infusions, and a continuous perineural sciatic catheter, all of which provided no relief. His pain scores and answers to supplemental questions showed significant pain in which he avoided usual activities and had significant disturbances in general activity, mood, sleep, and level of stress.

With the patient's multiple areas of healing soft tissue back injuries, the decision was made to avoid neuraxial stimulation and proceed with a trial of PNS. Informed consent for the therapy was obtained. Under ultrasound guidance, a 14-gauge epidural needle was guided to the sciatic nerve proximal to the popliteal bifurcation. A Medtronic™ (Minneapolis, MN) 1 × 8 compact lead was then threaded such that the middle electrode contacts corresponded to the middle of the target nerve. For the patient's left foot, 2 leads were placed in an anterior and posterior configuration using a cross-sectional view of the sciatic nerve (Fig. 1). Initial settings achieved adequate coverage and paresthesia was minimized without sacrificing analgesia.

Figure 1: Midthigh view of sciatic nerve after anterior electrode placement.

After placement, the patient reported a decrease in his pain from a 6 (DVPRS: “pain is hard to ignore and causes avoidance of usual activities”) to a 2 (DVPRS: “pain is noticeable but does not interfere with activities”). Furthermore, he fully participated in physical therapy the next day, and his opioid dosing was decreased by 80% (morphine equivalents: 410 mg per day ⇒ 90 mg per day) in the next 2 weeks. All indices of his DVPR Supplemental Questionnaire improved: general activity (9 ⇒ 5), mood (9 ⇒ 4), sleep (9 ⇒ 4), and level of stress (9 ⇒ 4). In these initial weeks, the patient experienced severe pain when he turned off his stimulation unit. After 2 weeks of PNS, the patient's wounds were fully healed and he transitioned to a 2-week neuraxial stimulation trial. After 4 weeks of stimulation (peripheral + neuraxial stimulation), the patient no longer required stimulation for pain control. His neuraxial stimulator was discontinued, and the patient continues to have minimal pain, improved muscle tone and mass, and significantly improved motor function.

Patient 2

A 34-year-old active duty soldier was involved in a mortar blast sustaining numerous orthopedic and lower extremity vascular injuries. After vascular repair, the patient was treated with therapeutic enoxaparin for 6 months.

The patient quickly developed severe bilateral neuropathic pain in his feet. He described this pain as a constant burning sensation with frequent spikes that disturbed sleep. On examination, the patient's left foot had notable sensory deficits in tibial and common peroneal distributions with preserved motor function. In his right foot, significant sensory and motor deficits in tibial and common peroneal distributions were noted. The patient was trialed on IV/oral opioids, nortriptyline, gabapentin, pregabalin, memantine, lidocaine patch, transcutaneous electrical neural stimulation units, numerous ketamine infusions, and perineural sciatic catheter placement. Using the same pain assessment tools, his pain scores and answers to supplemental questions showed significant pain in which he avoided usual activities and had significant disturbances in general activity, mood, sleep, and level of stress.

Because of his therapeutic anticoagulation, the multidisciplinary pain team decided he was a candidate for a trial of bilateral ultrasound-guided sciatic PNSs. Insertion was conducted in a similar manner to patient 1, but bilateral dual peripheral stimulator leads were placed. The patient reported a decrease in his pain from a 6 (DVPRS scale: hard to ignore, avoid usual activities) to a 2 (DVPRS scale: notice pain, does not interfere with activities). Over the next few days, the patient used no IV opioids for pain control and his oral opioids were weaned (morphine equivalents: 142 mg per day before placement ⇒ 83 mg per day 2 weeks after placement). All indices of the DVPRS Supplemental Questionnaire improved as well except level of stress (general activity (8 ⇒ 5), mood (9 ⇒ 3), sleep (4 ⇒ 1), and level of stress (3 ⇒ 4). The patient was able to participate in physical therapy and was discharged from inpatient care. The patient also noted that stopping stimulation resulted in return of severe pain. As an outpatient, the patient's oral narcotics were weaned, and his PNSs were maintained for 4 weeks. He subsequently underwent permanent implantation with excellent pain control. However, after lead displacement in his right extremity, he is awaiting explantation because his pain is now controlled on an outpatient regimen.

DISCUSSION

There is a paucity of information regarding neuromodulation in the setting of acute trauma–related neuropathic pain. Pain relief after PNS in both patients allowed a significant decrease in opioid dosage and improved functionality suggesting a need for further investigations focused on acute neuromodulatory therapies. PNS may be an additional tool for patients who do not respond to standard treatments for acute trauma–related neuropathic pain.

The use of ultrasound-guided PNS placement for neuropathic pain was described by Huntoon et al.^16–18 in a chronic pain population where they reported 75% of patients experiencing ≥50% pain relief. Numerous series also have reported the efficacy of PNS; however, these involved surgical implantation where the risk of perineural scarring is greater.^14,19,20 PNS benefit is thought to stem from interruption of A-δ and C fiber signaling.^21,22 Our experience with these 2 patients was similar to what Huntoon and Burgher.¹⁶ described as a “small therapeutic window” in relation to PNS. This was evident as both patients required numerous reprogramming sessions to gain accurate coverage and analgesia.

Although unique in presentation, both patients share common traits. Both had either absolute (patient 2: therapeutic Lovenox dosing) or relative contraindications (patient 1: with numerous open healing wounds being treated for prior infection) to neuraxial stimulation.²³ Although there are still inherent risks for PNS placement with such comorbidities, we chose to use PNS as a bridge until spinal cord stimulation (SCS) could be used. Additionally, both patients underwent PNS trials <5 months from their injury. Furthermore, both patients had pain symptoms resistant to perineural local anesthesia and ketamine infusions, which have been described as useful adjuncts in neuropathic pain.^24,25 Finally, both patients, although reporting the presence of pain 2 weeks after placement, displayed clinically significant improvements in their DVPRS ratings of mood, sleep, general activity, and level of stress.

Patient 1 (<3 months after injury) was notable as he was able to wean his opioid usage and no longer needed stimulation after 4 weeks (peripheral + neuraxial stimulation). It is unclear whether peripheral or neuraxial stimulation (or both) provided the continued improvement in this patient's pain. However, early neuromodulatory therapy in acute traumatic-related neuropathy is emphasized in this case. Thus, although intended as a bridge to SCS, this patient displayed significant resolution of his pain after a limited duration of stimulation. No trial has been undertaken to study early neuromodulatory therapies in humans. However, in a rat model of neuropathic pain, significant improvements in mechanical allodynia were appreciated in rats that received early SCS.²⁶ Although neuropathic pain models suggest that central sensitization occurs early after injury via a time-dependent glutamatergic and GABAergic mechanism, proximity of neuromodulatory therapy to the time of injury may be essential for efficacy and possible long-term outcome.^26,27

In our population, young, highly functional soldiers are exposed to unique combat injuries. Early interventions focused on functional optimization and opioid de-emphasis are essential. This case report suggests a possible role for neuromodulatory therapies in acute trauma–related neuropathic pain patients.

DISCLOSURES

Name: Michael Kent, MD.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: Michael Kent approved the final manuscript.

Name: Justin Upp, MD.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: Justin Upp approved the final manuscript.

Name: Christopher Spevak, MD, MPH, JD.

Contribution: This author helped write the manuscript.

Attestation: Christopher Spevak approved the final manuscript.

Name: Clarence Shannon, MD.

Contribution: This author helped write the manuscript.

Attestation: Clarence Shannon approved the final manuscript.

Name: Chester Buckenmaier, III, MD.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: Chester Buckenmaier, III, approved the final manuscript.

This manuscript was handled by: Spencer S. Liu, MD.