Multimodal assessment of patients with disorders of consciousness

A realistic scenario after coma is that a patient suffers from a disorder of consciousness(or DOC). This ranges from complete unawareness (UnresponsiveWakefulnessSyndrome) to consistent but fluctuating signs of awareness(Minimally Conscious State). In these cases, it is crucial to make a correctdiagnosis as it will impact clinical management. This thesis introduces thebackground of clinical (Chapter 1) and auxiliary (Chapter 2) assessments ofDOC patients. Four original research projects are presented in this thesis.In the first study of this thesis (Chapter 3), the brain’s structural changesin DOC patients were studied. Atrophy was more severe for patients thatwere longer in a DOC, mostly so for unconscious patients. Furthermore, regionalwhite and grey matter volume were found to discriminate differentawareness levels. The wide availability of MRI makes this technique appealingfor diagnostic purposes. The most important grey matter regionsfor diagnosis encompass the default mode network. This network is strictlyrelated to consciousness.Given the centrality of the default mode network for consciousness, thesubsequent study investigated how glucose metabolism in this network dependson its white matter structural integrity (Chapter 4). Afunction–structurerelationship was observed in brain-damaged patients for most of the defaultmode network regions. The relationship between thalamic glucose uptakeand thalamocortical tracts was stronger in patients who recovered from thedisorder of consciousness, suggesting an important role for the thalamus inrecovery of consciousness.In the last chapter (Chapter 5) of this thesis simultaneously acquired FDGPETand high-density EEG were combined to evaluate the diagnostic accuracyof both techniques, and to study cerebral electro-metabolic coupling. Inthe first study we show that the diagnostic accuracy of high-density EEG wascomparable to that of FDG-PET. In the second study we investigate how EEGand glucose uptake are related to each other at the regional level. Theta activityhas been suggested to originate from the default mode network andis positively related to glucose uptake in healthy control subjects. Alpha isimportant for relaxation and information processing, but also informationsuppression, and is negatively related to glucose uptake. These effects are reverted in patients with disorders of consciousness, which could be relatedto low default mode network activity and limited information processing.To conclude, this thesis shows that objective neuroimaging measures,specifically derived from T1-weighted structural MRI and EEG, are promisingto complement clinical diagnosis. Second, by combining various neuroimagingtechniques we can study the relationship between brain structureand function which can provide important contributions to neuroscience ingeneral.