Abstract
To the Editor
Akabari et al studied 28 patients who underwent decompressive surgery for cervical myeloradiculopathy, whereby only 9 (32%) had a ‘positive change’ intraoperatively, defined as a decrease in latency of 10% or an increase in motor evoked potential (MEP) amplitude of 50% with transcranial electrical stimulation (TES). It was concluded that patients showing this had significant functional improvement at 6 months postoperatively compared to those without. 1
This was seen in contrast to our findings in 69 patients, whereby 100% improvement in MEP amplitude alone was evident in 53% receiving 5 pulses and 72% receiving 9 pulses with TES. We also demonstrated that supramaximal MEP amplitude was achieved with a lower TES intensity in the 9 pulse protocol compared to the 5 pulse protocol. 2
Akabari et al did not specify the TES protocol utilized, but the above comparison suggests that they may not have achieved supramaximal MEP amplitude intraoperatively. This aspect, as demonstrated in previous studies employing the triple stimulation technique 3 or with multi-train TES, 4 may even lead to false negative results during intraoperative monitoring (IOM). 5
While the authors have attempted to control for age, disease duration, operating time and blood loss in this small study, it is necessary to standardize their TES protocol, 6 as well as the recording muscles for MEP. 7 These fundamental aspects were also not addressed in 2 previous studies of a similar nature.8,9
To that end, a stable and supramaximal baseline MEP elicited with a standardized and efficacious TES protocol is a crucial first step for evaluating intraoperative MEP changes, and a prerequisite for IOM in spinal surgery. This should be in place before any further prognostication study be performed. Future research in this area should ideally be designed to incorporate these aspects, so as to ensure the validity of findings. 2
ORCID iD
Yew Long Lo https://orcid.org/0000-0002-7448-2642