Dr. Jan Claassen
NewYork-Presbyterian/
“Our study suggests that patients with hidden consciousness can hear and comprehend verbal commands, but they cannot carry out those commands because of injuries in brain circuits that relay instructions from the brain to the muscles,” says study leader Jan Claassen, MD, chief of critical care and hospitalist neurology at NewYork-Presbyterian/
Our study suggests that patients with hidden consciousness can hear and comprehend verbal commands, but they cannot carry out those commands because of injuries in brain circuits that relay instructions from the brain to the muscles.
— Dr. Jan Claassen
The findings from the Recovery of Consciousness Following Intracerebral Hemorrhage (RECONFIG) study, which were published in Brain on August 14, 2023, could help physicians more quickly identify brain-injured patients who might have hidden consciousness and better predict which patients are likely to recover with rehabilitation.
“Disorders of consciousness have been known for a long time,” says Dr. Claassen on an episode of NewYork-Presbyterian’s Advances in Care podcast. “[Researchers] describe this state as a deep sleep that somebody could not be awakened from.”
However, over the years, physicians began to discover that patients who appeared unresponsive could be conscious.
Uncovering Hidden Consciousness in Patients with Brain Injury
Hidden consciousness, also known as cognitive motor dissociation (CMD), occurs in about 15% to 25% of patients with brain injuries stemming from head trauma, brain hemorrhage, or cardiac arrest.
“As a physician, sometimes you go to the bedside and have this gut feeling that there’s more there. I can’t really put it into words,” says Dr. Claassen. “I thought, ‘we should think about [conducting] a study where we study patients that have acute brain injury and are unconscious and see whether we can identify any patient with CMD early after brain injury.’”
Dr. Claassen would have conversations with families about their unconscious loved ones’ wishes for life-sustaining treatment. “A decision is made based on the assumption of what the patient would want to do. Not what the family wants to do, not what the physician wants to do, but what the patient would want to do,” he says. “I thought that it would be fundamentally important to try to find out whether we can become better and more precise at predicting the ultimate outcome of these patients because that would then feed into goals-of-care discussions in the long-term.”
In previous research conducted at NewYork-Presbyterian/
Brain MRI scans of two CMD patients
“[We found that] 15% of the patients [in our initial study] had CMD,” says Dr. Claassen. The study also showed that patients with CMD had a much higher chance of recovering behavioral features of consciousness before hospital discharge. “When we looked a year after the injury, 44% of the patients with CMD had functional recovery,” he says.
In a second observational cohort study, Dr. Claassen and colleagues screened 598 patients with acute brain injury. The study results, published in the Lancet Neurology in 2022, found CMD in 14% of the cohort, and confirmed the previous research showing that CMD was an independent predictor of shorter recovery time.
However, the precise pathways in the brain that become disrupted in this condition were unknown.
Brain Circuits Disrupted in Patients with Hidden Consciousness
In the RECONFIG and CONSCIOUSNESS studies, Dr. Claassen and his laboratory used the previously described EEG technique with 107 brain injury patients. The technique can determine when patients are trying, though unable, to respond to a command such as “keep opening and closing your right hand.”
The analysis detected CMD in 21 of the patients. The researchers then analyzed structural MRI scans for all patients.
“Using a technique we developed called bi-clustering analysis, we were able to identify patterns of brain injury that are shared amongst patients with CMD and contrast to those without CMD,” says co-lead author Qi Shen, PhD, associate research scientist in the Claassen lab and an expert in signal processing, machine learning, and biostatistics.
CMD (green) vs. non-CMD patients (red) anatomical distribution of lesion patterns on structural MRI
The researchers found that the CMD patients had intact brain structures related to arousal and command comprehension, supporting the notion that these patients were hearing and understanding the commands but were unable to carry them out.
“We saw that CMD patients had deficits in brain regions responsible for integrating comprehended motor commands with motor output, preventing CMD patients from acting on verbal commands,” says Dr. Claassen.
The findings may allow researchers to better understand which brain injury patients have CMD, which will be useful for clinical trials that support recovery of consciousness.
More research is required before these approaches can be applied to clinical practice. “However, our study shows that it may be possible to screen for hidden consciousness using widely available structural brain imaging, moving the detection of CMD one step closer to general clinical use,” Dr. Claassen says.
“Not every critical care unit may have resources and staff that is trained in using EEG to detect hidden consciousness, so MRI may offer a simple way to identify patients who require further screening and diagnosis,” Dr. Claassen says. He hopes to democratize this research for all neurologists and neurointensivists to use so that treatment for CMD can occur anywhere using basic tools.
Our study shows that it may be possible to screen for hidden consciousness using widely available structural brain imaging, moving the detection of CMD one step closer to general clinical use.
— Dr. Jan Claassen
The RECONFIG and CONSCIOUSNESS studies are continuing enrollment. Dr. Claassen hopes that through this study, and future research, they can become more precise and accurate in outcome predictions. “In some ways, it’s like personalized medicine,” he says. “Every patient is different, and you take into account all of the factors that influence outcome and that’s how we could come up with a more precise, long-term prediction for recovery.”
A version of this article originally appeared on Columbia University Irving Medical Center’s website. Click here to listen to Dr. Claassen discuss hidden consciousness and his research on CMD on the Advances in Care podcast.
Our study shows that it may be possible to screen for hidden consciousness using widely available structural brain imaging, moving the detection of CMD one step closer to general clinical use.
— Dr. Jan Claassen
