1 in 4 Unresponsive Coma Patients May Retain Some Awareness

At least 25% of unresponsive patients with a disorder of consciousness show signs of brain activity, an estimate that is higher than previous studies suggest.

“We found that at least 1 in 4 patients who are unresponsive to commands might actually be quite present and highly cognitive,” study investigator Nicholas D. Schiff, MD, Feil Family Brain & Mind Research Institute and Department of Neurology, Weill Cornell Medicine, Rockefeller University Hospital, New York, told Medscape Medical News.

“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 on August 14 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 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.

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 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.

Higher Rate of Awareness Than in Previous Research

The investigators noted that the percentage of participants with CMD in their study was up to 10 percentage points higher than in previous studies. This may be due to the multimodal approach that classified participants undergoing assessment with both fMRI and EEG on the basis of responses on either technique, they said. 

The median age was lower among participants with CMD than those without CMD (30.5 years vs 45.3 years).

Compared with participants without CMD, a higher percentage of those with such dissociation had brain trauma as an etiologic factor (65% vs 38%) and a diagnosis of minimally conscious state–minus on the CRS-R (53% vs 38%).

Among people with CMD, 18% were assessed with fMRI only, 22% with EEG only, and 60% with both fMRI and EEG.

Schiff noted that the use of both fMRI and EEG appears to be more sensitive in detecting brain activity during tasks compared with use of one of these techniques alone.

Of the 112 participants with a diagnosis of minimally conscious state–plus or who had emerged from the minimally conscious state, 38% had a response to commands on task-based fMRI, task-based EEG, or both. Among these participants, 23% were assessed with fMRI only, 19% with EEG only, and 58% with both fMRI and EEG.

Research shows “it’s very clear that people with severe brain injury continue to get better over time,” noted Schiff. “Every month and week matters, and so it probably is the case that a lot of these patients are picking up the level of recovery, and the later we go out to measure them, the more likely we are to find people who are CMD than not.”

These new results should prompt further study to explore whether detection of CMD can lead to improved outcomes, the investigators noted. “In addition, the standardization, validation, and simplification of task-based fMRI and EEG methods that are used to detect cognitive motor dissociation are needed to prompt widespread clinical integration of these techniques and investigation of the bioethical implications of the findings.”

All study participants with chronic brain injury had survived their initial illness or injury and had access to a research facility with advanced fMRI and EEG capabilities. “This survival bias may reflect greater cognitive reserve and resilience over time among the participants. As such, the results of our study may not be generalizable to the overall population of patients with cognitive motor dissociation,” the investigators wrote.

Another study limitation was that participating sites used heterogeneous strategies to acquire, analyze, and interpret data, which led to differences in the number, type, and ordering of the cognitive tasks assessed on fMRI and EEG.

“These differences, along with variations in recruitment strategies and participant characteristics, may have contributed to the unequal percentage of participants with cognitive motor dissociation observed at each site. Our findings may therefore not be generalizable across all centers,” the researchers wrote. 

Only a few academic medical centers have the specially trained personnel and techniques needed to assess patients for CMD — which, the researchers noted, limits the feasibility of performing these assessments in general practice.

Challenging Research

Commenting for Medscape Medical News, Aarti Sarwal, MD,  professor of neurology and section chief, Neurocritical Care, Virginia Commonwealth University, Richmond, Virginia, noted that this was a “very challenging” study to perform, given that only a few academic centers are equipped to perform both fMRI and quantitative EEG analysis.

“In general, finding patients this far out, who have access to clinical, radiological, and electrophysiological testing and were provided good care enough to receive these, is a mammoth task in itself.” 

Sarwal said the study builds on efforts of the Curing Coma Campaign , a clinical, scientific, and public health effort of the Neurocritical Care Society to tackle the concept of coma as a treatable medical entity.

“It continues to highlight the challenges of prognostication in acute brain injured patients by showing a higher presence of cognitive function than previously perceived,” she said.

Sarwal believes that the study’s largest impact is underscoring the need for more research into understanding the degree and quality of cognitive processing in patients with a disorder of consciousness. But it also underlines the need for a “healthy debate” on the cost – benefit analysis of pursuing such research, given the limited number of patients with access to resources. 

“This debate needs to include the caregivers and families outside the traditional realms of stakeholders overseeing the science.” 

Although communication with comatose patients is still “a ways away,” this research is “a step in the right direction,” said Sarwal. 

The study was funded by the James S. McDonnell Foundation and others. Schiff and Sarwal report no relevant financial disclosures.