Neuroimaging Biomarkers for Disorders of Consciousness
Neuroimaging Biomarkers for Disorders of Consciousness
After a severe traumatic brain injury (TBI) or stroke, the differential diagnosis between coma, vegetative state (now called unresponsive wakefulness syndrome), minimally conscious state, and locked-in syndrome can be complex, because of the absence of communication.
Behavioral assessment scales, such as the CRS-R, have been developed (2) and are superior to a diagnosis based on clinical consensus. However, some patients may still be misclassified. Neuroimaging can be a window into the brain of these non-communicative patients. In 2010, our group published a groundbreaking paper (3) in which several patients who were thought to be in the vegetative state (i.e. unconscious) showed similar functional MRI activations, on mental imagery tasks, as healthy volunteers, thereby revealing signs of preserved consciousness. However, more than 5 years later, the translation from bench to bedside is still challenging (4).
Using resting-state fMRI, we have shown that the connectivity of the default mode network (DMN) was positively correlated with the degree of consciousness (5). FDG-PET, measuring the brain’s metabolic activity, is more sensitive than fMRI regarding the differential diagnosis between the disorders (6). While these imaging studies have focused on patients at the chronic stage, our French colleagues have designed a diffusion tensor imaging (DTI)-based index (7), which could be used as an early predictor of the outcome, supporting decisions in the ICU.
Among the electrophysiological biomarkers for disorders of consciousness, the perturbational complexity index (PCI), calculated by perturbing the cortex with transcranial magnetic stimulation (TMS) to engage distributed interactions in the brain and by compressing the spatiotemporal pattern of these electrocortical responses (EEG) to measure their algorithmic complexity, is the most promising (8).
The quest for biomarkers in disorders of consciousness, and for early predictors of the outcome, is not only a medical challenge. While treatment options are still limited, a better diagnosis and early prediction can have a significant psychological and societal impact, for the patient, his/her family, and for healthcare professionals (1,4). Several cases, largely reported in the media because of the patient’s popularity or because of legal battles regarding end-of-life decisions, illustrate well the ethical issues raised by disorders of consciousness and the need for more objective biomarkers.
European Congress of Radiology 2015
References
Laureys et al. Lancet Neurology 2004.
Schnakers et al., BMC Neurol. 2009.
Monti et al. N Engl J Med 2010.
Hermoye et al. Future Neurology 2013.
Vanhaudenhuyse et al. Brain 2009.
Stender et al. Lancet 2014.
Galanaud et al. Anesthesiology 2012.
Casali et al. Sci Transl Med 2013.