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]
Abstract
OBJECTIVE:
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.
METHODS:
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.
RESULTS:
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.
CONCLUSIONS:
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.”
http://journals.lww.com/neurotodayonline/Fulltext/2016/11170/Simple_Test_of_Electromyography_on_Arms_Reliably.8.aspx
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