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.
Dr. 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 Dr. 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.