Case Report: Neuromonitoring Alert in Spinal Cord Stimulator Surgery

In a previous post, I described methods for optimizing spinal cord stimulator (SCS) placement under anesthesia with the use of neuromonitoring. In that post, I described the stages of SCS surgery, the recommended monitoring plan, and different neurophysiological methods for mapping the laterality of the electrode. If you’re not familiar with this surgical procedure, you should read the first part of that post just to get oriented.

Introduction:

SCS placement surgery can be performed with the patient either awake or asleep. While it is becoming increasingly uncommon, performing this procedure on an awake patient has two benefits: 1) it allows for ongoing neurological assessment, and 2) electrode placement and SCS programming can be optimized with direct feedback from the patient. Due to a variety of risks associated with operating on awake patients, surgeons are increasingly opting to perform this surgery with the patient under anesthesia. Because the patient cannot respond to commands, or give feedback, we need surrogate methods for neurological assessment and optimizing electrode placement. That’s where neuromonitoring comes in.

Operating on the spinal cord carries obvious risk, and there are reports in the literature of iatrogenic spinal cord injury resulting in paralysis during SCS placement surgery (Kumar et al., 2007; Levy et al., 2011; Smith et al., 2010; Meyer et al., 2007; Barolat et al., 2005; Tamkus et al., 2015). Oddly, many surgeons forego the “neurological assessment” capabilities of neuromonitoring during these procedures, and opt only for “optimizing electrode placement” with EMG. In other words, the surgeons are offered MEPs and SSEPs to monitor the function of the spinal cord, and they decline these tests; taking on what I consider to be unnecessary risk.

In the case report below, I present a neuromonitoring alert during spinal cord stimulator surgery. In this procedure, MEPs and SSEPs warned the surgeon of impending spinal cord injury, and likely saved the patient from a negative outcome.

Note: I did not monitor this case, and I am totally blind to the identify of the patient, surgeon, hospital, etc. A colleague of mine provided the de-identified data.

H&P and Preop Planning:

History: The patient is a 50 year old male with a history of lumbar radiculopathy and now complaining of low back pain s/p failed lumbar laminectomy and instrumented fusion surgery. He is ambulatory without assistance. Of note on radiographic imaging, there is stenosis at the T8/T9 level. Diagnosis: chronic pain syndrome & failed back surgery.

Surgical Plan: T9/10 laminotomy for T8/9 implantation of epidural paddle electrode, tunneling for implantation of of pulse generator, programming of spinal cord stimulator.

Neuromonitoring Plan: Transcranial electric motor evoked potentials (tceMEPs) from bilateral first dorsal interosseous (FD), rectus abdominis (RA), quadriceps (QD), tibialis anterior (TA) and abductor hallucis (AH) muscles; somatosensory evoked potentials (SSEPs) from bilateral ulnar nerve (UN) and posterior tibial nerve (PTN); train of four (TOF) from left PTN to left AH and from right PTN to right AH; spontaneous (S) and electrically-triggered (T) electromyography (EMG) from bilateral RA, QD, TA and AH; 2-channel electroencephalography (EEG).

Anesthesia Plan: TIVA (Propofol+Remifentanil) for induction and maintenance of anesthesia, 20 mg Rocuronium to facilitate ETT placement. No inhalational anesthetics.

Intraoperative Events:

Baseline Description: “s/p prone positioning, TOF is consistent with adequate clearance of neuromuscular blockade for reliable tceMEP and EMG monitoring (T4:T1>70%). Correct positioning of 2 soft bite blocks verified prior to tceMEP stimulation. TceMEPs successfully recorded from bilateral FD, RA, QD, TA & AH, and are of sufficient size and consistency for reliable monitoring. UN and PTN SSEPs are bilaterally present and reliable for monitoring. Surgeon informed of and acknowledged all baseline recordings. Anesthesia team informed there is no evidence of impending brachial plexopathy, and depth of hypnosis is adequate for incision.”

14:50: “T9/10 laminotomy Complete. TOF is 4/4 without fade, consistent with adequate conduction across the NMJ for reliable monitoring of EMG and MEPs. No remarkable (neurotonic, A-train) EMG activity observed. MEPs and SSEPs are unremarkable relative to baseline, consistent with unchanged spinal cord sensorimotor conduction. Surgeon informed, acknowledged. Prep for placement of paddle electrode.” 

14:55: “ALERT: right PTN SSEP exhibits >10% latency shift and amplitude attenuation during placement of padle electrode. Left PTN SSEP remains within acceptable limits of baseline. MAP = 96 mmHg. Surgeon informed and acknowledged. Surgical pause and request for MEP test.”

Figure 1: Here are the SSEP data. Refer to 14:55 traces.

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Figure 1: At 14:55, SSEPs begin to deteriorate.

14:56: “ALERT (cont’d). s/p MEP test, MEPs from bilateral lower extremities are markedly attenuated in amplitude (left RA; bilateral QD & TA; right AH). MEPs recorded from left AH are unremarkable relative to baseline, consistent with intact motor conduction to the left foot. Surgeon informed, acknowledged.”

Figure 2: Here are the left side MEP data. Refer to 14:56 traces.

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Figure 2: At 14:56, MEPs from the left RA, QA & TA show amplitude attenuation. Left AH remains consistent with baseline.

Figure 3: Here are the left side MEP data. Refer to 14:56 traces. 

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Figure 3: At 14:56, a test of the right side revealed absent MEPs from the QA, TA and AH muscles. It’s hard to see because of scaling, but there is a small AH response present that shows minimal improvement (see Figure 4).

Figure 4: With the screen gain changed, we can see partial recovery of the MEP recorded from the right AH, without recovery of the MEPs recorded from the ipsilateral TA and QA muscles. 

 

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Figure 4: The scale of the EPs from Figure 3 has been changed to show MEPs present from the right AH muscle. The baseline trace was removed to make this response more visible. The surgeon is immediately notified of the change in data.

15:01: “ALERT (cont’d). SSEPs are now attenuated bilaterally. MEPs remain as described previously.”

After several minutes of a surgical pause with MAP >90 mmHg, the MEPs and SSEPs did not exhibit enough improvement to justify continuing with the procedure. As a result of these observations, the paddle electrode was removed and the surgery was aborted.

Post-op Findings:

Upon emergence, the patient was able to move both distal lower extremities: however, he exhibited asymmetric, proximal lower extremity weakness (right weaker than left). The patient’s neurological function improved rapidly post-op, and displayed full symmetrical strength in PACU.

Summary:

The present case report demonstrates how neuromonitoring of spinal cord function can alert the surgeon to impending spinal cord injury. The outcome is a “true positive” because neuromonitoring correctly detecting impending spinal cord injury, which was evidenced by the patient’s post-op weakness. While the patient made a full recovery, he will probably not be able to have their pain treated with a SCS because the surgery in this case is too risky. So, that’s a major drawback to aborting the surgery – the patient will probably continue to live with intractable pain.

Inevitably, some people will read this case report and argue that we don’t know for certain if the patient would have been any worse off without neuromonitoring. In other words, in the absence of MEP/SSEP monitoring, the surgery would have been completed and it’s entirely possible that the patient may have emerged from surgery with the exact same outcome, except he would have a SCS in place to actually treat the pain. Since we don’t know for certain whether or not the patient would have emerged paralyzed or neurologically-intact (at least partially), some will argue that the benefit of neuromonitoring remains questionable. Furthermore, as the argument goes, the incidence of post-op deficit secondary to SCS surgery is reportedly low (~0.6%), usually resolves, and may not justify the cost MEP/SSEP monitoring in every case. In this era of cost-cutting in medical care, some surgeons may opt for MEP/SSEP monitoring in only the most risky of cases, or simply not at all.

While these arguments have some semblance of validity, I don’t share the perspective. I think, if there is risk to the spinal cord, then it should be appropriately monitored with the endeavor to reduce or eliminate that risk. If the choice of whether or not to protect someone’s spinal cord were taken out of the hands of the surgeons who don’t monitor, the payors who don’t pay, and the legislators who don’t understand, and placed into the hands of the patients who may or may not become paralyzed, I wonder if we would see more or less MEP/SSEP monitoring during SCS placement. Of course, I could probably extend this topic and easily go on-and-on about the stupidity of our over-reliance on meta-analyses and randomized, placebo-controlled, double-blind experiments…. but I digress.

Personally, I’ve seen quite a few MEP alerts during SCS placement or removal. I think MEPs and SSEPs are useful in these procedures. What do you guys think? What do you think about this case report? Feel free to post your comments and questions below.

Oh, and Happy New Year!!

References:

  1. Barolat G, Peacock WJ, Staudt LA. Pain and spasticity. In: Benzel EC, ed. Spine surgery: techniques, complication avoidance, and management, Vol. 2, 2nd ed. Philadelphia: Elsevier Churchill Livingstone, 2005.
  2. Kumar K, Taylor R, Jacques L et al. Spinal cord stimulation versus conventional medical management for neuropathic pain: a multicenter randomized controlled trial in patients with failed back surgery syndrome. Pain 2007;132:179–188.
  3. Levy R, Henderson J, Slavin K et al. Incidence and avoidance of neurologic complications with paddle type spinal cord stimulator leads. Neuromodulation 2011;14:412–422.
  4. Meyer SC, Swartz K, Johnson JD. Quadriparesis and spinal cord stimulation: case report. Spine 2007;32:565–568.
  5. Tamkus AA, Scott AF, Khan FR. Neurophysiological Monitoring During Spinal Cord Stimulator Placement Surgery. Neuromodulation. 2015;18(6):460-464.

7 thoughts on “Case Report: Neuromonitoring Alert in Spinal Cord Stimulator Surgery

  • Reply Ellen Snider February 2, 2016 at 14:12

    Commenting on your statement: “….the incidence of post-op deficit secondary to SCS surgery is reportedly low (~0.6%)” – Are you aware of any published data that looks at incidence of post-op deficit secondary to stimulator placement by level-lumbar, thoracic, cervical?

    Also, on your summary point “Personally, I’ve seen quite a few MEP alerts during SCS placement or removal.” It would be great to see a comparison of your SSEP and MEP findings in your series of SCS cases, and the respective post-op outcome findings. My personal bias, based on similarly published comparisons of SSEP and MEP data from Idiopathic Scoliosis, is that MEP monitoring leads to much higher alarm rates than SSEP with little evidence to support that these higher rates of alarm are in fact true positives that would have resulted in post op neurologic complications gone undetected by unchanged SSEP.

    • Reply Richard Vogel February 2, 2016 at 16:18

      Hi Ellen,

      Great comments. I’m not aware of any data that look at incidence of post-op deficit secondary to stimulator placement by level of the spine. Regarding your second point, I’m not doing a case series, but if I did, I’d certainly want to make that comparison. With marked attenuation or loss of MEPs in SCS placement/removal surgery, I’ve seen patients wake up fine, while others wake up weak and recover. The former is more frequent. I think there is a lot of evidence to support your bias, and we obviously take each patient independently and make decisions about the data at hand. I personally don’t look at attenuated/lost MEPs as telling me whether or not the patient, if awake, would exhibit neurologic complications. Rather, I look at them as telling me that some part of the nervous system has been perturbed. The motor change has opened a window of opportunity to identify and resolve that perturbation. If left unresolved, that window begins to close and the likelihood of post-op deficit increases. Of course, we draw our conclusions from surgical context, patient variables and multiple IONM modalities, to get the clearest picture and make the most accurate prognosis.

  • Reply John-Paul April 10, 2016 at 11:13

    Hello Dr. Vogel
    I recently monitored a Cervical SC Stim case, lost UE SSEPs upon initial placement, surgeon was alerted and ackn. Proceeded with testing EMG (only proximal CMAPs obtained) Surgeon adj paddle Lost LE SSEPs. surgeon again alerted and ackn. I then started to document and prove it was not technical crawling under drape and testing UE stimulation electrode impedances (patient was wrapped and in Mayfied unable to get a UE peripheral on). All stim electrodes were under 5Komhs and balanced. LE had peripheral pick up from Abd Hal. Post op patient woke up with paralysis and paresis. Emergency removal and motor function returned. Patient has proprioception deficits and is going to rehab.

    Meps were declined, however how often are MEPs an indicator of post op deficits when anesthesia is never optimal where I work? I felt 100% confident in my calling the changes to SSEPs since this was a posterior cervical surgery and SSEPs are the most reliable EP in IOM.

    I love all your articles and tips for monitoring!

    • Reply John-Paul April 10, 2016 at 11:14

      Forgot to add I requested paddle be removed and surgeon declined that too!

      • Reply Richard Vogel April 10, 2016 at 15:44

        Hello. Interesting case. There are certainly numerous reports in the literature of paralysis during SCS placement surgery, and I’ve certainly seen a few cases where we lost MEPs, aborted, and the patient woke with mild, transient weakness. We’ve all read about cases where patients are monitored with SSEPs only, and they wake paralyzed with no changes in the SSEPs. Strange that we always have to remind surgeons that it’s a test of sensory function, not motor function. In Philadelphia, every surgeon who does SCS implants under general anesthesia uses MEPs, but I know every region is different. There are plenty of surgeons out there who don’t use IONM at all. When you do use IONM, though, as a surgeon you have to use it correctly and pay attention to the results. Otherwise, what’s the point? From what I can tell, it sounds like you managed the case well. You recommended MEPs, surgeon declined. You identified evolving injury from your data (MEPs might have detected this earlier). You recommended removing the electrode, surgeon declined. Hopefully that’s all documented. Sometimes, sadly, the best that you can do is make the right recommendations, interpret the data accurately, communicate well and document thoroughly. If the surgeon doesn’t want to listen, there’s not much you can do, but you can rest a little easier knowing you did your job well.

  • Reply Sanjeev Jaswal July 4, 2016 at 13:49

    I have intra operative neuromonitoring reports of my son who underwent unsuccessful corrective spine surgery. I was told IOM do not show any sign of deficiency. Is it possible and can some one analyse the reports and tell me what went wrong. I do not understand these graphs. I agreed for the surgery only because this monitoring was to be used. I can send the reports. Pl provide me Email ID.

  • Reply Dr Alan Forster July 9, 2017 at 04:31

    Was papaverine tried? as well as reversing last surgical event eg putting paddlein, resting, increasing BP (NB BP at the cord!!), papaverine will work in some – I tend to see this in glioma removal with corticospinal tracts,where in one case we lost MEP’s at least 10times, resting & papaverine on each occasion giving gradual recovery, guiding but leaving no deficit………..might have made it possible to complete the surgery if papaverine had been tried??

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