Dorsal root ganglion stimulation lead fractures: potential mechanisms and ways to avoid
- 1 Anesthesiology, Chronic Pain Divison, UPMC, Pittsburgh, Pennsylvania, USA
- 2 Pain Management, Cleveland Clinic Foundation, Cleveland, Ohio, USA
- Correspondence to Dr Gaurav Chauhan; CHAUHANG@UPMC.EDU
Abstract
Dorsal root ganglion stimulation (DRGS) therapy is a rapidly emerging tool being used by pain physicians in the treatment of chronic pain. Complex regional pain syndrome (CRPS), a debilitating disease whose mechanism is still has yet to be fully elucidated, is a common pathology targeted by DRGS therapy, often better results than traditional spinal cord stimulation. DRGS therapy, however, is not bereft of complications. Lead migration and fracture are two examples in particular that are among the most common of these complications. The authors report an unusual case of lost efficacy due to lead fractures in patients with CRPS treated with DRGS. The case report narrates identification, management and probable mechanism of DRGS lead fracture. The structural instability of DRGS leads can yield distressing symptoms at any point during the therapy, and physicians should be cognisant of the complications of DRGS therapy.
Background
Complex regional pain syndrome (CRPS) is one of the most debilitating and clinically challenging chronic pain conditions.1 The underlying mechanism of neural injury in CRPS, still not fully understood, implicates a complex inflammatory process which phenotypically presents with unremitting symptoms of pain or allodynia of affected area, trophic changes of skin and appendages, abnormal vasomotor tone and sudomotor patterns, increased stiffness of affected joints and in rare cases tremor, myoclonus or fixed dystonia.1 2
CRPS has an estimated incidence of 5.5–26.2 cases per 100 000 patient-years, which extrapolates to approximately 200 000 patients with CRPS in the USA.3 4 Due to the lack of prophylactic or preventive treatments, the therapeutic rationale for CRPS is limited to symptom management that facilitates rehabilitation to preserve and improve the function of the affected limb.5 In recent years, DRGS, a neurostimulation technique developed to target dorsal root ganglia (DRG), has proved to be superior to conventional treatment for patients with CRPS.6
The DRG is located in the intervertebral foramen, comprised of primary sensory neurons, and plays a vital role in the development, modulation and maintenance of chronic pain pathways.7–9 DRGS is also more cost-effective and superior than conventional dorsal column spinal cord stimulation (SCS) in CRPS.10 Preliminary data on the DRGS therapy for CRPS have reported significantly higher success rates (74.2% for DRGS vs 53% for SCS), more precise relief of the painful areas with better quality pain relief (95% for DRGS vs 61% for SCS) equivalent or better safety profile as compared with the SCS therapy.11 However, DRGS therapy, approved for clinical use in 2016, is still relatively speaking in its infancy, and with time the device-related complications and their potential issues will become more apparent. The authors report an unusual case of DRG lead fractures in patients with CRPS of the lower extremities.
Case presentation
The patient gave informed consent for the case report. A 56-year-old Caucasian woman, on DRGS therapy for CRPS, presented at our pain clinic with episodes of sudden electrical shock-like sensation in her back, cramping pain in her calf muscles along with involuntary plantar flexion of feet. The patient was diagnosed with CRPS type I of right leg, based on Budapest criteria 2 years ago.12 At the time of diagnosis, the patient reported allodynia, hyperalgesia, temperature asymmetry and a reduced range of motion of the right ankle joint. The patient also had a severe limitation of the outdoor activities. The patient further reported that she has a desk job at a law firm and is contemplating filing for a disability claim.
The patient had suboptimal pain control with gabapentin (1200 mg three times daily), Non- Steroidal anti-inflammatory drugs (NSAIDs), lidocaine 5% patches and tricyclic antidepressants (amitriptyline 30 mg at bedtime). The patient was deemed to be an appropriate candidate for DRGS after appropriate psychological evaluation. A successful DRGS trial followed, with lead placement at the right L4 level, with a more than 70% decrease in her pain. Subsequently, the patient underwent an uneventful DRGS lead placement at the right L4 and L5 levels. At 1-week and 3-month follow-up after the DRGS implant, the patient reported more than 75% decrease in her pain. The patient also reported that she was able to complete her physical therapy sessions with minimal discomfort. A year after the implant, the patient continued to maintain gainful employment and reported resolution of the left foot swelling, skin sensitivity, erythema and antalgic gait.
After 1.5 years of improved function and significant pain relief, the patient reported that she felt mild electrical shock sensation in her left foot, in addition to a sudden onset of involuntary plantar flexion which eventually resolved after approximately 1 min. The patient had switched-off her device since the episodes of electrical shock-like pain. The patient also reported a few episodes of sudden cessation of stimulation a few days prior to the episode, despite adequately charging the device.
Investigations
The patient underwent fluoroscopic evaluation of the DRGS leads in lumbar spine that reported no overt disconnections of the leads and pulse generator, and both leads were found to be in relatively appropriate anatomic positions (figure 1). On interrogation of the DRGS leads, the impedance levels were found to be high (up to 6000 ohm) at all contacts (each contact was tested up to manufacturer recommended maximum of 600 mA). The decision was made to proceed with the DRGS lead revision. On extraction, both of the leads were found to contain fractures of the wires inside the leads while the plastic coating was intact (figure 2).
Intact dorsal root ganglion (DRG) stimulator at the right L4 and L5 neuroforamen. The leads appear to be intact with no apparent cracks or breaks.
Closer examination of the dorsal root ganglion stimulator lead revealed that the wires inside the lead was fractured while the sheath around the lead was intact.
Outcome and follow-up
The patient was made aware of the new findings, and she agreed to undergo reimplantation of the DRGS leads. Subsequently, the DRGS leads were again placed at the right L4 and L5 with appropriate levels of impedance. At 6 months after the procedure, the patient continues to have excellent pain relief from the newly implanted leads without complication.
Discussion
DRGS therapy is not bereft of complications. Sivanesan et al analysed the Manufacturer and User Facility Device Experience database for DRGS devices and identified 979 unique DRGS-related incidents.13 Sivanesan et al reported that device-related complications (47%) were most common, followed by procedural complications (24.2%) such as new neurological symptoms, dural punctures, infections and haematoma, patient complaints (12.2%), such as implantable pulse generator (IPG) site pain and unwanted stimulation and serious adverse events (2.4%). In the majority of cases, the mainstay of troubleshooting was surgical revision (49.8%) rather than explant (16.4%). The most common device-related complications were lead migration (59.1%) and lead damage (21.5%) followed by hardware malfunction (5.2%), lead connection failure (1.7%), erosions (4.1%) and sheath damage (1.3%).13
The device-related complications are attributed to the ergonomics of the DRGS lead placement and the design engineering of the leads. The DRGS leads have a much smaller cross-sectional area, contact size and are much less rigid than the conventional SCS leads.7 This design engineering of the DRGS leads is to accommodate placement in the tiny space around the DRG, enhance manoeuvrability, placement within intervertebral foramen and the creation of strain relief loops.7 To a certain degree, the structural integrity of the lead is compromised to achieve better lead flexibility. An increased manipulation for the formation of strain loops during the lead placement further compounds the problem by inducing microfractures along the length of the leads, making them susceptible to breakage, kinks and fractures.13 Furthermore, the fixed space at the dorsal intervertebral foramen, where the lead is placed, further accentuates the effect of postural or traumatic strain on the leads.7 13 Small damage in the insulation of the lead may occur during the insertion of the DRGS lead as a result of friction between the lead and the sheath or rarely the epidural needle used for placement.14 The loss of insulation and the proximity of the damaged lead to the DRGS may lead to overstimulation, stimulation of unwanted region or the neurological sequelae that may be transient in nature.8 15
The damage to the DRG lead in our patients appears primarily to the wire component of the leads. There was no damage in the insulation coat of both leads. The break in the circuit ultimately caused the increased impedance malfunction of the lead. It seems that the repetitive folding and the looping of the lead can induce stress weak points along the lead. These points on the lead, depending on the placement, may act as a hinge and undergo repetitive cycles of stress and strain during spinal movement, as well as paraspinal muscle repetitive tension with pressure force exerted against adjacent bony structures, thus accumulating fatigue fractures leading to varying degrees of gross structural deformities in the lead’s wires while the plastic insulation of the leads might sustain such stress for a longer time. That is the most logic explanation of what our patients sustained in the cases described in this report. The loss of insulation and the proximity of the damaged lead to the DRGS may lead to overstimulation, stimulation of unwanted region or the neurological sequelae that may be transient in nature.8 15
The authors unanimously agree that some of the measures to reduce mechanical damage to the SCS lead might be effective for DRGS lead as well. The epidural needle, used for introducing the sheath containing the DRGS leads, should be inserted at a low angle to minimise the bending force of the interspinous ligament, ligamentum flavum and the paraspinal muscles on the soft DRG leads after removal of the epidural needle and the sheath. That might decrease the shearing effect of the friction between the ligaments and muscles, and relatively less rigid DRGS leads. Of note, also injecting normal saline into the sheath before loading the DRG lead will decrease the surface tension and minimise the friction between the rigid sheath and the very soft and malleable DRG lead.13 14
In addition, limiting the repetitive acute folding and bending of the DRGS lead may minimise the fatigue load and damage to the microstructural elements of the lead. In a case of newly onset neurological symptoms and/or loss of benefit of the DRGS, a physician should maintain a high index of suspicion for DRGS lead fracture or migration. The diagnostic algorithm should start with checking impedance and interrogation of the current pattern of stimulation followed by simple X-rays of the spine to rule out gross hardware anomalies such as IPG disconnections or lead migration/fracture. It is prudent to explant the device as, in some cases, a closer examination of the DRGS lead may reveal the extent of damage, unapparent on X-rays.
These cases add to the database on the potential complications of DRGS therapy. At this point, there is a consensus among chronic pain physicians that DRGS therapy is safe, superior and more cost-effective for a patient with CRPS than conventional SCS. As the DRGS therapy becomes more prevalent, with time, it will become apparent if the similar events are sporadic cases or a part of the natural clinical course of the DRGS therapy due to the inherent elements of the anatomy of the back and design of the DRG leads. The latter might require re-examination of the lead design as well as the procedural aspects of DRGS. The physicians should be cognisant of the complications of DRGS therapy. In the case of newly onset neurological symptoms, it is vital to assume causality due to the implanted neuromodulation device, and the diagnostic algorithm should be aimed at that. The patient should be adequately informed and counselled, and the continuation of therapy should be based on shared decision-making between the patient and the provider.
Learning points
-
Dorsal root ganglion stimulation (DRGS), a rapidly emerging tool in the pain physician’s arsenal in the treatment of CRPS, is bereft of complications.
-
It is important to improve the implant surgical technique to avoid or reduce the fractures of the leads.
-
Newly onset neurological symptoms and/or loss of pain relief from DRGS may be due to DRGS lead fracture or migration.
-
The diagnostic algorithm should start with checking impedance and interrogation of the current pattern of stimulation followed by simple X-rays of the spine to rule out gross hardware anomalies.
-
In some cases, it is prudent to explant the device as a closer examination of the DRGS lead may reveal the extent of damage, unapparent on X-rays.
Footnotes
-
Contributors GC: Drafting of the manuscript, proofreading. BIR: Drafting of the manuscript. NM: Defining the intellectual content, proofreading.
-
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
-
Competing interests None declared.
-
Provenance and peer review Not commissioned; externally peer reviewed.
- © BMJ Publishing Group Limited 2021. No commercial re-use. See rights and permissions. Published by BMJ.
References
Use of this content is subject to our disclaimer