DOI: 10.1097/BRS.0b013e3181d4ed2f
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PMID: 24736515
Issn Print: 0362-2436
Publication Date: 2010/03/15
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Excerpt
We would like to comment on the recent paper by Modi et al.1 Does the case in question serve as the first definitive example of a “false negative” for MEP monitoring? We would argue the answer is “no.” Instead, a more likely explanation for the unfortunate outcome of this case can be found hidden within this paper's Figure 2.1
The key point made by the authors was that intraoperative MEPs did not show significant change, yet the patient awoke with paraplegia. However, Figure 2B shows a >50% decline or outright loss of MEP responses in 3 of the 4 monitored muscle groups. This change persists through Figures 2C and 2D for muscles innervated by the C8–T1 levels (presumably hand muscles). But why would MEPs be lost in the hands bilaterally, without change from muscles in the legs (S1–S2 levels)? And why would this change not be mentioned by the authors? Individual MEP responses within this Figure are difficult to resolve, because the high sensitivity of the screen display causes the responses to obscure one another. Nevertheless, it's clear that the apparent latency to MEPs in the leg muscles is considerably less than that for responses in the hands. Again, how can this be?
The one explanation that can unify these anomalies is that electrodes from the hand muscles were mistakenly switched with those from leg muscles when making connections to the intraoperative monitoring amplifiers. This would explain the unusual response latencies, and more importantly, would show that changes in MEP responses did, in fact, predict this patient's postoperative paraplegia.
Other questions about pulse-train number, stimulus intensity, and changes in artifact can be raised from Figure 2. All of these points emphasize the intricacies involved in correctly implementing and interpreting transcranial MEP monitoring.
