Neuromodulation: Technology at the Neural Interface Received: October 13, 2014
Revised: November 24, 2014
Accepted: December 26, 2014
(onlinelibrary.wiley.com) DOI: 10.1111/ner.12273
Neurophysiological Monitoring During Spinal Cord Stimulator Placement Surgery Arvydas A. Tamkus, MD*; Andrew F. Scott, MSE*; Fahd R. Khan, MD† Objectives: The objective of this retrospective study was to study the frequency of intraoperative neuromonitoring (IONM) alerts during the spinal cord stimulator (SCS) placement surgery, postoperative neurological complications and effectiveness of Somatosensory evoked potential (SSEP) and electromyography (EMG) methods to determine laterality of the SCS lead placement. Materials and Methods: Records of 111 consecutive SCS placement surgeries monitored by a commercial IONM company between August 1, 2013 and December 31, 2013 were reviewed. IONM alerts, surgical interventions, and patient outcomes were assessed. Results: Significant decreases of lower extremity SSEPs following the placement of the SCS paddle electrodes into the epidural space were recorded in two (1.9%) patients prompting alerts to the surgeons and removal of the electrode. Somatosensory system dysfunction due to stimulated limb malpositioning was identified by continuous SSEP in four cases (3.8%). All waveform changes resolved and SSEP waveforms returned back to baselines in all six patients after adjustments were made. There was no evidence of sustained neurological injury in any patients in this study. The location of the stimulator was adjusted based on IONM feedback in 8/43 (18.6%) cases. Conclusions: IONM is an effective tool in detecting potential neurological event and facilitating lead placement and potentially avoiding revision surgery. Keywords: Intraoperative neuromonitoring, neurologic complications, somatosensory evoked potentials, spinal cord stimulator Conflict of Interest: Authors confirm that there are no conflicts of interest associated with this publication.
INTRODUCTION
460
The implantation of spinal cord stimulator (SCS) systems has been widely used as an effective and safe treatment for pain. Neuropathic chronic pain, failed back surgery syndrome, ischemic leg pain, arachnoiditis, complex regional pain syndrome and peripheral neuropathy are among the most commonly treated conditions. SCS reduces pain intensity by creating a non-painful tingling paresthesia experienced by the patient. The mechanism of action for SCS is still elusive, but is thought to be primarily due to segmental activation of A beta afferents, blocking of transmission in the spinothalamic tract, supra spinal inhibition, activation of neurotransmitters and neuromodulators, and antidromic activation of pain afferents (1,2). Adverse events during SCS placement are reported to be quite frequent, but life-threatening complications are rare. In a systemic review Turner et al. (3) found that the weighted complication average was 34% with the most common adverse event being stimulator revision for lead repositioning with an additional operation. Other complications include superficial and deep infections, including epidural abscess. Another database review performed by Taylor et al. (4) found that 43% of patients experienced one or more complications following SCS implantation; although no major adverse events were reported. Kumar et al. (5) in a randomized controlled trial found that the principal complications were electrode migration (10%), infection and wound breakdown (8%), and loss of therapeutic effect/paresthesia (7%). Intraoperative neuromonitoring (IONM) is advocated in certain instances to facilitate placement of SCS electrodes. Several studies www.neuromodulationjournal.com
also have reported that IONM can be used for neuroprotection during SCS electrode implantation surgery. Mammis and Mogilner (6) reported successful paddle lead placement in a series of 78 patients under general anesthesia using the electromyography (EMG) method. Somatosensory evoked potentials (SSEPs) also were performed with no changes reported and no neurological complications. Air et al. (7) also reported successful lead laterality placement for 19 patients under general anesthesia using the EMG method. As in the Mammis and Mogilner study, SSEPs were recorded, but no alerts or neurological complications were reported. None of the cited studies reported neurological complications, or IONM alerts leading to surgical intervention to avoid injury. However there were few case studies reporting postoperative weakness following SCS placement (Table 1). Smith et al. (9) reported four patients with post-SCS placement paraparesis secondary to cord contusion, hematoma, and implantation in the setting of broad based thoracic disc herniations. Meyer et al. (10) reported quadriplegia secondary to dural puncture during lead placement. Barolat et al. (11) published a case in which patient suffered a spinal cord injury resulting in quadriplegia after needle penetration in the lower
Address correspondence to: Arvydas Tamkus, MD, 812 Avis Dr. Ann Arbor, MI 48108, USA. Email: [email protected] * Biotronic NeuroNetwork, Ann Arbor, MI, USA; and † Department of Neurosurgery, Stanford University, Stanford, CA, USA Sources of financial support: no significant financial support.
© 2015 International Neuromodulation Society
Neuromodulation 2015; 18: 460–464
IONM DURING SCS PLACEMENT SURGERY
Table 1. Summary of the Literature Reported Complications After SCS Placement. Author (year)
Type of study
Complications
Turner et al., (2004) (3)
Systemic review (22 studies)
Stimulator revision 23.1% Stimulator removal 11.0% Equipment failure 10.2% Pain in stimulator region 5.8% Superficial infection 4.5% Biological complications 2.5% Deep infection 0.1%
Taylor et al., (2004) (4)
Systemic review (18 studies)
Electrode problems 27% Infections 6% Generator problems 6% Extension cable problems 10% CSF leaks 7%
Kumar et al., (2007) (5)
Randomized controlled study (214 patients)
Electrode migration 10%
Manufacturers’ data base review (44,587 patients)
Major motor deficit 0.25%
Levy et al., (2011) (8)
Infection or wound breakdown 8% Loss of paresthesia 7%
Limited motor deficit 0.14% Autonomic changes 0.013% Sensory deficit 0.1% Epidural hematoma 0.19% CSF leaks 0.05%
Smith et al., (2010) (9)
Case report (4 patients)
Paraparesis
Meyer et al., (2007) (10)
Case report (1 patient)
Quadriparesis
Barolat et al., (2005) (11)
Case report (1 patient)
Quadriplegia
cervical cord. In a review of the scientific publications Levy et al. (8) confirmed that many case series do not report SCS complications and concluded that the true incidence of neurological complications cannot be determined from this literature. Therefore, they studied manufacturers’ own databases and found the complication rates to be 0.54% for neurological complications and 0.05% for cerebrospinal fluid leaks. Based on this information, the incidence of spinal cord injury after SCS implantation is unknown and probably underreported. Therefore we performed a retrospective analysis of 111 consecutive patients to analyze the incidence of IONM alerts during SCS placement surgery and postoperative outcomes.
MATERIALS AND METHODS
www.neuromodulationjournal.com
SSEP Protocol SSEPs were recorded using posterior tibial nerve (PTN) stimulation at the ankle and median nerve (MN) or ulnar nerve (UN) stimulation at the wrist. Stimulus parameters were as follows: pulse duration 0.2–0.3 msec; repetition rate: 0.5–5 Hz; stimulus intensity: 5–50 mA. Recordings were performed from cortical, subcortical, and peripheral montages. Recording parameters included: filter bandpass: 10–40 Hz–500 Hz (for cortical recordings), 30 Hz–3000 Hz (for subcortical and peripheral recordings); sweep 100 msec, number of averages: 100–300. IONM alert criteria: repeatable 50% or greater decrease in amplitude from the immediately preceding waveform in all cortical and subcortical SSEPs.
EMG Protocol EMG was recorded from myotomes correlating with the surgery level including upper and lower extremities and abdominal muscles. Filter bandpass: 10 Hz–1000 Hz.
IONM Protocol for Lead Placement Lateralization IONM protocol for lead placement lateralization was performed using either SSEP collision testing and/or antidromic dorsal column activation leading to EMG activity Stimulation through the paddle lead causing decrease of the SSEP amplitude or generation of the recordable EMG responses was considered as a positive testing result. Protocol was used as previously published by Balzer et al. (12) and Shils and Arle (13).
Equipment and Electrodes IONM was implemented using commercially available instrumentation (Xltek Protektor, Natus-Xltek, Inc., San Carlos, CA, USA; or Axon NIM-Eclipse, Medtronic Xomed, Jacksonville, FL, USA). Thirteen-millimeter disposable stainless steel needle electrodes (Rhythmlink, Columbia, SC, USA) were used for IONM stimulation and recordings.
RESULTS One hundred eleven consecutive IONM charts of patients operated during the five-month time period were reviewed for the study. Demographics and diagnosis are summarized in Table 2. Patients were operated on by 44 surgeons at 26 different hospitals and medical centers. Medtronic, St. Jude Advanced Neuromodulation Systems, or Boston Scientific Advances Bionics paddle electrodes were used. All surgeries were performed under general anesthesia. One hundred six patients (95.5%) were monitored for neuroprotection using upper (MN or UN) and lower (PTN) extremity SSEP. Significant SSEP changes were recorded during six surgeries.
© 2015 International Neuromodulation Society
Neuromodulation 2015; 18: 460–464
461
This study was reviewed and approved for exempt status as an anonymous retrospective study by the New England Investigational
Review Board. A retrospective review of records of 111 consecutive SCS placement surgeries monitored by a commercial IONM company between August 1, 2013 and December 31, 2013 was performed. IONM was performed for neuroprotection, lead lateralization, or both. SSEP and free-run EMG monitoring was performed for neuroprotection. SSEP collision and/or EMG activation were performed to facilitate placement of the paddle leads.
TAMKUS ET AL.
Figure 1. Patient F/56, with chronic neuropathic pain in left lumbar region radiating into left hip, left groin, and left leg down to foot. She underwent a T11 laminotomy for placement of a Medtronic 5-6-5 paddle electrode. During initial placement of the paddle electrode an adhesion in the epidural space was encountered and the electrode veered to the left, which was noticed during fluoroscopic guidance. This caused the left lower limb cortical response amplitudes to significantly decline to
Revised: November 24, 2014
Accepted: December 26, 2014
(onlinelibrary.wiley.com) DOI: 10.1111/ner.12273
Neurophysiological Monitoring During Spinal Cord Stimulator Placement Surgery Arvydas A. Tamkus, MD*; Andrew F. Scott, MSE*; Fahd R. Khan, MD† Objectives: The objective of this retrospective study was to study the frequency of intraoperative neuromonitoring (IONM) alerts during the spinal cord stimulator (SCS) placement surgery, postoperative neurological complications and effectiveness of Somatosensory evoked potential (SSEP) and electromyography (EMG) methods to determine laterality of the SCS lead placement. Materials and Methods: Records of 111 consecutive SCS placement surgeries monitored by a commercial IONM company between August 1, 2013 and December 31, 2013 were reviewed. IONM alerts, surgical interventions, and patient outcomes were assessed. Results: Significant decreases of lower extremity SSEPs following the placement of the SCS paddle electrodes into the epidural space were recorded in two (1.9%) patients prompting alerts to the surgeons and removal of the electrode. Somatosensory system dysfunction due to stimulated limb malpositioning was identified by continuous SSEP in four cases (3.8%). All waveform changes resolved and SSEP waveforms returned back to baselines in all six patients after adjustments were made. There was no evidence of sustained neurological injury in any patients in this study. The location of the stimulator was adjusted based on IONM feedback in 8/43 (18.6%) cases. Conclusions: IONM is an effective tool in detecting potential neurological event and facilitating lead placement and potentially avoiding revision surgery. Keywords: Intraoperative neuromonitoring, neurologic complications, somatosensory evoked potentials, spinal cord stimulator Conflict of Interest: Authors confirm that there are no conflicts of interest associated with this publication.
INTRODUCTION
460
The implantation of spinal cord stimulator (SCS) systems has been widely used as an effective and safe treatment for pain. Neuropathic chronic pain, failed back surgery syndrome, ischemic leg pain, arachnoiditis, complex regional pain syndrome and peripheral neuropathy are among the most commonly treated conditions. SCS reduces pain intensity by creating a non-painful tingling paresthesia experienced by the patient. The mechanism of action for SCS is still elusive, but is thought to be primarily due to segmental activation of A beta afferents, blocking of transmission in the spinothalamic tract, supra spinal inhibition, activation of neurotransmitters and neuromodulators, and antidromic activation of pain afferents (1,2). Adverse events during SCS placement are reported to be quite frequent, but life-threatening complications are rare. In a systemic review Turner et al. (3) found that the weighted complication average was 34% with the most common adverse event being stimulator revision for lead repositioning with an additional operation. Other complications include superficial and deep infections, including epidural abscess. Another database review performed by Taylor et al. (4) found that 43% of patients experienced one or more complications following SCS implantation; although no major adverse events were reported. Kumar et al. (5) in a randomized controlled trial found that the principal complications were electrode migration (10%), infection and wound breakdown (8%), and loss of therapeutic effect/paresthesia (7%). Intraoperative neuromonitoring (IONM) is advocated in certain instances to facilitate placement of SCS electrodes. Several studies www.neuromodulationjournal.com
also have reported that IONM can be used for neuroprotection during SCS electrode implantation surgery. Mammis and Mogilner (6) reported successful paddle lead placement in a series of 78 patients under general anesthesia using the electromyography (EMG) method. Somatosensory evoked potentials (SSEPs) also were performed with no changes reported and no neurological complications. Air et al. (7) also reported successful lead laterality placement for 19 patients under general anesthesia using the EMG method. As in the Mammis and Mogilner study, SSEPs were recorded, but no alerts or neurological complications were reported. None of the cited studies reported neurological complications, or IONM alerts leading to surgical intervention to avoid injury. However there were few case studies reporting postoperative weakness following SCS placement (Table 1). Smith et al. (9) reported four patients with post-SCS placement paraparesis secondary to cord contusion, hematoma, and implantation in the setting of broad based thoracic disc herniations. Meyer et al. (10) reported quadriplegia secondary to dural puncture during lead placement. Barolat et al. (11) published a case in which patient suffered a spinal cord injury resulting in quadriplegia after needle penetration in the lower
Address correspondence to: Arvydas Tamkus, MD, 812 Avis Dr. Ann Arbor, MI 48108, USA. Email: [email protected] * Biotronic NeuroNetwork, Ann Arbor, MI, USA; and † Department of Neurosurgery, Stanford University, Stanford, CA, USA Sources of financial support: no significant financial support.
© 2015 International Neuromodulation Society
Neuromodulation 2015; 18: 460–464
IONM DURING SCS PLACEMENT SURGERY
Table 1. Summary of the Literature Reported Complications After SCS Placement. Author (year)
Type of study
Complications
Turner et al., (2004) (3)
Systemic review (22 studies)
Stimulator revision 23.1% Stimulator removal 11.0% Equipment failure 10.2% Pain in stimulator region 5.8% Superficial infection 4.5% Biological complications 2.5% Deep infection 0.1%
Taylor et al., (2004) (4)
Systemic review (18 studies)
Electrode problems 27% Infections 6% Generator problems 6% Extension cable problems 10% CSF leaks 7%
Kumar et al., (2007) (5)
Randomized controlled study (214 patients)
Electrode migration 10%
Manufacturers’ data base review (44,587 patients)
Major motor deficit 0.25%
Levy et al., (2011) (8)
Infection or wound breakdown 8% Loss of paresthesia 7%
Limited motor deficit 0.14% Autonomic changes 0.013% Sensory deficit 0.1% Epidural hematoma 0.19% CSF leaks 0.05%
Smith et al., (2010) (9)
Case report (4 patients)
Paraparesis
Meyer et al., (2007) (10)
Case report (1 patient)
Quadriparesis
Barolat et al., (2005) (11)
Case report (1 patient)
Quadriplegia
cervical cord. In a review of the scientific publications Levy et al. (8) confirmed that many case series do not report SCS complications and concluded that the true incidence of neurological complications cannot be determined from this literature. Therefore, they studied manufacturers’ own databases and found the complication rates to be 0.54% for neurological complications and 0.05% for cerebrospinal fluid leaks. Based on this information, the incidence of spinal cord injury after SCS implantation is unknown and probably underreported. Therefore we performed a retrospective analysis of 111 consecutive patients to analyze the incidence of IONM alerts during SCS placement surgery and postoperative outcomes.
MATERIALS AND METHODS
www.neuromodulationjournal.com
SSEP Protocol SSEPs were recorded using posterior tibial nerve (PTN) stimulation at the ankle and median nerve (MN) or ulnar nerve (UN) stimulation at the wrist. Stimulus parameters were as follows: pulse duration 0.2–0.3 msec; repetition rate: 0.5–5 Hz; stimulus intensity: 5–50 mA. Recordings were performed from cortical, subcortical, and peripheral montages. Recording parameters included: filter bandpass: 10–40 Hz–500 Hz (for cortical recordings), 30 Hz–3000 Hz (for subcortical and peripheral recordings); sweep 100 msec, number of averages: 100–300. IONM alert criteria: repeatable 50% or greater decrease in amplitude from the immediately preceding waveform in all cortical and subcortical SSEPs.
EMG Protocol EMG was recorded from myotomes correlating with the surgery level including upper and lower extremities and abdominal muscles. Filter bandpass: 10 Hz–1000 Hz.
IONM Protocol for Lead Placement Lateralization IONM protocol for lead placement lateralization was performed using either SSEP collision testing and/or antidromic dorsal column activation leading to EMG activity Stimulation through the paddle lead causing decrease of the SSEP amplitude or generation of the recordable EMG responses was considered as a positive testing result. Protocol was used as previously published by Balzer et al. (12) and Shils and Arle (13).
Equipment and Electrodes IONM was implemented using commercially available instrumentation (Xltek Protektor, Natus-Xltek, Inc., San Carlos, CA, USA; or Axon NIM-Eclipse, Medtronic Xomed, Jacksonville, FL, USA). Thirteen-millimeter disposable stainless steel needle electrodes (Rhythmlink, Columbia, SC, USA) were used for IONM stimulation and recordings.
RESULTS One hundred eleven consecutive IONM charts of patients operated during the five-month time period were reviewed for the study. Demographics and diagnosis are summarized in Table 2. Patients were operated on by 44 surgeons at 26 different hospitals and medical centers. Medtronic, St. Jude Advanced Neuromodulation Systems, or Boston Scientific Advances Bionics paddle electrodes were used. All surgeries were performed under general anesthesia. One hundred six patients (95.5%) were monitored for neuroprotection using upper (MN or UN) and lower (PTN) extremity SSEP. Significant SSEP changes were recorded during six surgeries.
© 2015 International Neuromodulation Society
Neuromodulation 2015; 18: 460–464
461
This study was reviewed and approved for exempt status as an anonymous retrospective study by the New England Investigational
Review Board. A retrospective review of records of 111 consecutive SCS placement surgeries monitored by a commercial IONM company between August 1, 2013 and December 31, 2013 was performed. IONM was performed for neuroprotection, lead lateralization, or both. SSEP and free-run EMG monitoring was performed for neuroprotection. SSEP collision and/or EMG activation were performed to facilitate placement of the paddle leads.
TAMKUS ET AL.
Figure 1. Patient F/56, with chronic neuropathic pain in left lumbar region radiating into left hip, left groin, and left leg down to foot. She underwent a T11 laminotomy for placement of a Medtronic 5-6-5 paddle electrode. During initial placement of the paddle electrode an adhesion in the epidural space was encountered and the electrode veered to the left, which was noticed during fluoroscopic guidance. This caused the left lower limb cortical response amplitudes to significantly decline to
