“We found that at least 1 in 4 patients who are unresponsive to commands might actually be quite present and highly cognitive,” said study investigator Nicholas D. Schiff, MD, Feil Family Brain & Mind Research Institute and Department of Neurology, Weill Cornell Medicine, Rockefeller University Hospital, New York.
“In other words, if you go to the bedside and carefully examine someone with a severe brain injury and find no evidence of responsiveness, no one has been able to give you an a priori number to say how likely you are to be wrong in thinking this person is actually unaware, not processing language, and not capable of high-level cognitive work. And the answer to that now is at least 1 in 4 times.”
The findings were published online in The New England Journal of Medicine.
Clinical Implications?
Cognitive motor dissociation (CMD) is a condition whereby patients with a severe brain injury who are unresponsive to commands at the bedside show brain activity on functional MRI (fMRI) or electroencephalography (EEG) when presented with selective motor imagery commands, such as “imagine playing tennis,” or “ imagine opening and closing your hand.”
Previous research shows that CMD is present in 10%-20% of people with a disorder of consciousness, a rate similar to that in patients with acute or chronic brain injury.
Understanding that a patient who appears unconscious has signs of cognitive processing could change the way clinicians and family interact with such individuals. Unresponsive patients who are aware may eventually be able to harness emerging communication technologies such as brain-computer interfaces.
In addition, knowing an individual’s CMD status could aid in prognosis. “We know from one study that there’s a four times increased likelihood that patients will be independent in a year in their function if they have cognitive motor dissociation,” said Dr. Schiff.
Unlike most previous studies of CMD, which were conducted at single sites and had relatively small cohorts, this new study included 353 adults with a disorder of consciousness (mean age, 37.9 years; 64% male) at six multinational sites.
Participants were recruited using a variety of methods, including consecutive enrollment of critically ill patients in the intensive care unit and enrollment of those with chronic illness or injury who were in the postacute phase of brain injury.
Response to Commands
Study participants were at different stages of recovery from an acute brain injury that had occurred an average of 8 months before the study started.
To determine the presence or absence of an observable response to commands among participants, trained staff used the Coma Recovery Scale–Revised (CRS-R); scores on this instrument range from 0 to 23, and higher scores indicate better neurobehavioral function.
About 40% of individuals were diagnosed with coma or vegetative state, 29% with minimally conscious state–minus, and 22% with minimally conscious state–plus. In all, 10% had emerged from a minimally conscious state.
Researchers assessed response to timed and repeated commands using fMRI or EEG in participants without an observable response to verbal commands, including those with a behavioral diagnosis of coma, vegetative state, or minimally conscious state–minus, and in participants with an observable response to verbal commands.
Of the 353 study participants, 61% underwent at least one fMRI assessment and 74% at least one EEG assessment. Both fMRI and EEG were performed in 35% of participants.
Dr. Schiff explained the two assessment types provide slightly different information, in that they measuring different types of brain signals. He also noted that although “every medical center in the world” has EEG, many do not have fMRI.
The brain imaging assessments captured brain activity within the motor area of the frontal cortex when tasked with motor imagery.
Of the 241 participants deemed to be in a coma or vegetative state or minimally conscious state–minus on the basis of CRS-R score, 60 (25%) had a response to commands on task-based fMRI, task-based EEG, or both.
The percentage of participants with CMD varied across study sites, from 2% to 45%, but Dr. Schiff said the reason for this is unclear.
The proportion of participants with CMD may have been even higher if all individuals had been assessed with both imaging techniques, he said.