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.
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.
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.
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.
Figure 3: Here are the left side MEP data. Refer to 14:56 traces.
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.
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.
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.
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!!
- 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.
- 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.
- 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.
- Meyer SC, Swartz K, Johnson JD. Quadriparesis and spinal cord stimulation: case report. Spine 2007;32:565–568.
- Tamkus AA, Scott AF, Khan FR. Neurophysiological Monitoring During Spinal Cord Stimulator Placement Surgery. Neuromodulation. 2015;18(6):460-464.