Lesenfants D, Habbal D, Chatelle C, Schnakers C, Laureys S, Noirhomme Q.
Electromyographic decoding of response to command in disorders of consciousness. Neurology. 2016 Oct 21. pii: 10.1212/WNL.0000000000003333. [Epub ahead of print]
To propose a new methodology based on single-trial analysis for detecting residual response to command with EMG in patients with disorders of consciousness (DOC), overcoming the issue of trial dependency and decreasing the influence of a patient's fluctuation of vigilance or arousal over time on diagnostic accuracy.
Forty-five patients with DOC (18 with vegetative/unresponsive wakefulness syndrome [VS/UWS], 22 in a minimally conscious state [MCS], 3 who emerged from MCS [EMCS], and 2 with locked-in syndrome [LIS]) and 20 healthy controls were included in the study. Patients were randomly instructed to either move their left or right hand or listen to a control command ("It is a sunny day") while EMG activity was recorded on both arms.
Differential EMG activity was detected in all MCS cases displaying reproducible response to command at bedside on multiple assessments, even though only 6 of the 14 individuals presented a behavioral response to command on the day of the EMG assessment. An EMG response was also detected in all EMCS and LIS patients, and 2 MCS patients showing nonreflexive movements without command following at the bedside. None of the VS/UWS presented a response to command with this method.
This method allowed us to reliably distinguish between different levels of consciousness and could potentially help decrease diagnostic errors in patients with motor impairment but presenting residual motor activity.
Volitional EMG response to motor command was detected in all 13 MCS+ cases, even though only six of them had presented a behavioral response on the day of the EMG assessment. An EMG response was also detected in all three of the patients emerging from a MCS and both of the patients with locked-in syndrome.
The researchers noted, however, that the locked-in patients in their study were in an incomplete locked-in state, meaning they showed residual motor abilities. Had they suffered from complete or classic locked-in syndrome, no signal could have been detected on EMG.
None of the 15 patients in a vegetative state showed any response on EMG. While two of the MCS- patients did show a response, the authors were unwilling to conclude on that basis that they retain awareness, as the results could have been false positives.
One of the patients initially diagnosed as being in a vegetative state showed no initial response on the EMG test, but when the patient later recovered enough to be clinically diagnosed as being MCS+, the EMG test was positive.
“The biggest limitation of the study,” Dr. Lesenfants said, “is that the technique is motor-dependent, whereas EEG or fMRI-based brain-computer interfaces could offer motor-independence and allow the detection of responses to command in patients without motor abilities. Perhaps some of these vegetative patients retain some awareness and we just do not see it on EMG. The problem with brain-computer interfaces, on the other hand, is that many patients who show awareness behaviorally do not show it on the imaging. There are too many false negatives.”