Complications of Peripheral Nerve Stimulation: Open Technique, Percutaneous Technique, and Peripheral Nerve Field Stimulation

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Chapter 2 Complications of Peripheral Nerve Stimulation

Open Technique, Percutaneous Technique, and Peripheral Nerve Field Stimulation

Tory L. McJunkin, Paul J. Lynch, Elizabeth Srejic

Chapter Overview

Chapter Synopsis: Peripheral nerve stimulation (PNS) has emerged as an effective treatment for chronic neuropathic pain with the advantages of being cost effective, reversible, nonaddictive, and nonpharmacologic. Several approaches may be used for implantation and stimulation, including an open surgery technique (PNS:OT), a percutaneous implantation technique (PNS:PT), and a nonperineural technique called peripheral nerve field stimulation (PNfS). As the neuromodulatory techniques have evolved, side effects have become uncommon but should be considered as the treatments become more prevalent. Certain areas of implantation, notably the nerves of the brachial plexus, present greater risks than others. Infection ranks as the most common side effect, but technical problems such as lead migration or lead fracture can also arise. The risk of biologic complications is usually immediate; technical complications usually occur within 2 years of implant. Whereas surgical implantation (PNS:OT) of a stimulating electrode requires exploration and nerve visualization, PNS:PT relies on fluoroscopic imaging for guidance. PNfS places a stimulating device in the peripheral subcutaneous area of pain. As with any neurostimulation technique, a thorough patient selection process can increase the chances for success of the procedure and lower associated risks. A psychological assessment may be required in advance of implantation, but screening by response to nerve block is no longer indicated as predictive of success. Risk can be minimized with vigilance by the physician.

Important Points:

PNS is a neuromodulation technique involving application of an electrical current adjacent to peripheral nerves to treat chronic, intractable, debilitating neuropathic pain conditions that are refractory to less invasive treatments.

There are three main variants of PNS: PNS performed with an open surgical technique (PNS:OT); PNS executed with a percutaneous technique (PNS:PT), and a subcutaneous; nonperineural technique called peripheral nerve field stimulation (PNfS).

PNS techniques, which are reversible, cost effective, nonaddictive, and nonpharmacologic, are based on delivery of low-level electric impulses to pain-generating nerves via an implantable system, consisting of a programmable generator connected to electric transmission leads.

Common neural targets amenable to PNS include cranial nerves, occipital nerves, segmental truncal nerves, and upper and lower extremity plexus and peripheral nerves or areas not accessible or effectively treated by spinal cord or spinal nerve root stimulation.

The risk of serious problems resulting from PNS therapies appears to be relatively low in clinical practice, especially for PNfS. However, PNS therapy is not without risk, and lead placement along specific target areas may be more challenging technically than in other implantable therapies.

The most common complication is infection. Other reported complications include peripheral nerve trauma and damage to other tissues, pain over the device, and seroma.

Technical complications generally involve equipment failure, including lead migration and lead fracture, and less commonly, battery malfunction.

Devastating infectious and technical complications, although rare, have been reported and deserve special attention.

Biologic complications commonly occur within 3 months of implant, although infections can rarely present much later. Technical complications typically occur within 2 years of implant.

Meticulous attention to surgical technique is the best measure against the development of infection, the most common PNS complication. In addition, adequate patient screening, use of high-quality imaging, practitioner expertise, and familiarity with the different types of available hardware are recommended to preclude adverse outcomes.

Introduction

Peripheral nerve stimulation (PNS) is a neuromodulation technique in which an electrical current is applied adjacent to peripheral nerves to diminish pain. For the sake of this chapter, PNS techniques will describe stimulation of structures that are anatomically outside of the spinal canal. There are three main variants of PNS: PNS performed with an open surgical technique (PNS:OT); PNS executed with a percutaneous technique (PNS:PT); and a subcutaneous, nonperineural technique called peripheral nerve field stimulation (PNfS). No matter which technique is chosen, PNS is used for chronic, intractable, debilitating neuropathic pain conditions that are refractory to less invasive treatments.

Using PNS:OT, a lead, often a paddle lead, is surgically placed directly adjacent to the target nerve. An example is placement of a paddle lead along the sciatic nerve for a person with neuropathic sciatica. Using PNS:PT, a percutaneous lead is placed through a needle that is usually guided via a nerve stimulator or by ultrasonography. An example is placement of a percutaneous lead through a needle under ultrasound guidance along nerves of the brachial plexus for a painful brachial plexopathy. Using PNfS, which is also called subcutaneous field stimulation, a lead is typically placed through a needle into the subcutaneous tissue in the direct area of pain experienced by the patient, remote to named peripheral nerves. An example is a lead placed in the subcutaneous tissues for axial low back pain in a patient with postlaminectomy syndrome.¹

Neuromodulation has a fascinating history that long predates modern understanding of electricity. The Egyptians used electric stimulation to treat pain as early as 2500 bc, as seen on stone carvings depicting placement of electric catfish on people. In ancient Greece and Rome, torpedo fish were used to deliver electric shocks of as many as 200 volts (which may be sufficient to kill a human adult) to combat pain and common maladies such as headache, gout, and arthritis.

In contemporary times, PNS techniques, which are reversible, cost effective, nonaddictive, and nonpharmacologic, are based on delivery of low-level electric impulses to pain-generating nerves via an implantable system, consisting of a programmable generator connected to electric transmission leads. Over the past decade, they have been used increasingly to treat a wide range of conditions involving pain in peripheral or cranial neural distributions. In particular, they may be an effective treatment for neuropathic pain that is not accessible or effectively treated by spinal cord or spinal nerve root stimulation. Common neural targets amenable to PNS include cranial nerves (e.g., trigeminal peripheral terminal branches), occipital nerves, segmental truncal nerves (e.g., nerve root, intercostal, ilioinguinal, iliohypogastric, genitofemoral), and upper and lower extremity plexus and peripheral nerves (e.g., ulnar, median, radial, lateral femoral cutaneous, sciatic, anterior and posterior tibial nerves).²

Another reason PNS therapies have increased in popularity may be their lower incidence of complications. In spite of reported complications including infection, lead migration, and device failure, the risk of serious problems resulting from PNS or PfNS therapies appears to be relatively low in clinical practice. Although there has been no formal comparison of PNS versus spinal cord stimulation (SCS) complications, when compared with intrathecal drug delivery, electrical neuromodulation techniques rarely impact morbidity or mortality significantly.³

Notwithstanding the preceding, PNS therapy is not without risk, and lead placement along specific target areas may be more challenging technically than SCS therapy. For example, placement of PNS leads using an open or closed technique to treat nerves of the brachial plexus, which lie in close proximity to the subclavian and axillary vessels, might be associated with comparable or greater risks than SCS lead placement in the cervical epidural space to treat upper extremity neuropathic pain.

Selected Complications

Perhaps one of the most significant advantages of PNS is its relatively low rate of complications (Table 2-1). Mobbs et al⁴ mention relatively minor complications in their retrospective study (currently the largest in the literature), which examines the role of the implantable PNS device in the chronic pain patient. In 38 patients who received implanted PNS devices, six stimulators were removed after implantation (15%). Two were removed due to infection, representing a 5% infection rate. One of these patients had hemophilia despite factor VIII cover, and an episode of bleeding that was further complicated by infection, necessitating stimulator removal. Despite a positive result during the trial period, one stimulator was removed after one month because of minimal effect post-implantation. This patient subsequently improved again after his workers’ compensation issues were resolved. One stimulator was removed at 4 years post-implantation since the patient maintained it was no longer needed. Two stimulators in one patient had an initially positive effect, lasting 3 months, followed by a rapid decline in effect. The patient did not wish to have the stimulators re-trialed or re-implanted. A single lead had to be replaced as it was fractured following a fall from a tree. The stimulator continued to function following revision of the lead. During the follow-up period, two battery generators were replaced because of battery failure and a further two generator/lead combinations were repositioned as they were uncomfortable and restricted arm movement. One electrode was relocated during the trial period due to a substantial, uncomfortable motor effect in an adjacent muscle. A further 8 electrodes were resutured during the second operation due to electrode lead migration.

Table 2-1 Complications of PNS (OT; PT, fS)

Complication	Reported Rate (If Reported)
Overall revision rate	27%³²
Requiring explant	15%⁴
Procedural
Tissue trauma	Theoretical
Allergic reactions	Case reports,³³ * 0.8%³⁴
Specific anesthesia-related complications	Anecdotal evidence
Hemorrhage	Theoretical
Peripheral nerve trauma	60%⁴
Organ trauma	Theoretical
Post-Procedural
Infection	5%,⁴ 3%-5%,¹⁷ 4.5%,¹⁸ 1%³⁵
Seroma	2.5%³⁶
Lead migration	27%-33%,^34,³⁷ 2%³⁵
Skin erosion	12.5%,²¹ 7%³⁵
Pain at generator site	0.9%-5.8%^38,³⁹ *
Excessive bleeding	Theoretical
Sepsis	Theoretical, unpublished case report at the Cleveland Clinic
Battery failure/hardware failure	1.6%,⁴⁰ * 2%³⁵
Lead migration	33%,²⁷ 24%³⁰

* Extrapolated from spinal cord stimulation devices.

The overall risk of complications associated with PNS therapies appears to be very low. In contrast to SCS, PNS techniques target nerves external to the spinal canal, eradicating potential development of bleeding and infection within the epidural space, catastrophic central neurologic deficit, and emergent spine surgery. However, there exists a risk of a range of procedural, postprocedural, device-related, and infectious complications even when PNS is performed by the most experienced practitioners. Consequently, any physician who undertakes a PNS procedure must be prepared to manage any unexpected sequelae.

Before undertaking a PNS procedure, several factors should be considered, according to a review of surgical procedures pertaining to implantable neuromodulation technology.⁵ These factors include the incidence, severity, and time to resolution of complications, as well as the net impact on the patient given that complications may detract from the beneficial effect of the procedure.

One of the cornerstones of iatrogenesis avoidance in PNS is patient selection. This includes restricting PNS eligibility to patients with neuropathic pain who have failed to gain relief from more conservative therapies. Because infection is one of the most common complications of PNS procedures, patients must be free of serious skin and systemic infections and must not be immunocompromised. Furthermore, patients receiving PNS must be able to tolerate weaning from nicotine, steroids, and blood thinners and must be thoroughly prescreened to determine their psychological suitability for undergoing PNS procedures.

Procedural Complications

Common potential procedure-related complications surrounding PNS procedures involve tissue trauma, infection, allergic reactions, and anesthesia-related complications. In general, avoidance of such complications necessitates high-quality fluoroscopic guidance to promote optimal lead placement, as well as meticulous surgical technique to prevent infection from contaminated skin, implanted equipment, and other causes. However, development of complications from PNS procedures is still possible even with extensive preventive measures, use of technologically advanced equipment, and years of practitioner expertise.

Harm caused to tissues during PNS procedures may consist of bleeding, peripheral nerve trauma, and damage to vital structures (e.g., vessels and organs). Because vital internal structures are vulnerable in PNS, the use of high-quality fluoroscopy is indicated; for example, pneumothorax, a potential organ-related complication of PNS device installation in the thoracic region, is best circumvented by high-quality imaging.⁶ In deeper tissues, damage to vessels can be evaded by using an open rather than percutaneous technique, which may help to prevent blind injury of vasculature, embolism, and other negative sequelae.

Hemorrhage is a potential adverse outcome in any surgical procedure. In PNS, bleeding can occur in the region of the generator or lead incision, promoting hematoma and wound dehiscence. In some instances, serosanguineous fluid rather than blood may accumulate, leading to seroma. Both of these problems are limited to the area of surgery and do no usually result in life-threatening disorders.

Because the risk of excessive bleeding and seroma development exists, standard precautions against hemorrhage and fluid leakage should be exercised. Specifically, in the preoperative period, patients should discontinue medications likely to promote bleeding, and patients with a history of excessive bleeding should have a coagulation profile performed. During the procedure, the practitioner should focus on careful tissue dissection, containment of bleeding, and thorough inspection of the wound before closure. In addition, expert surgeons recommend irrigation and complete closure of surgical wounds to diffuse any sources of infection and restriction of pocket size to no larger than necessary to inhibit seroma formation.

The use of PNS therapy was commonly used to treat pain after previous nerve damage as described by Mobbs et al ⁴ in their retrospective study (currently the largest in the literature) of 38 patients implanted with 41 nerve stimulators. The previous nerve damage included blunt and or sharp nerve trauma (in 14 of 38 patients) and inadvertent injection of a nerve (in nine of 38 patients). The incidence of nerve damage from PNS therapy itself is unknown and believed to be rare. To avoid nerve damage, practitioners should maintain excellent knowledge of relevant anatomy and watch for patient neuralgia and radicular pain in the postoperative period. Treatment of suspected nerve injury may include steroid protocol, anticonvulsants, and referral for neurologic consult.

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