The Role of Neuroimaging Techniques in Establishing Diagnosis, Prognosis and Therapy in Disorders of Consciousness

Abstract

Non-communicative brain damaged patients raise important clinical and scientific issues. Here, we review three major pathological disorders of consciousness: coma, the unresponsive wakefulness syndrome and the minimally conscious state. A number of clinical studies highlight the difficulty in making a correct diagnosis in patients with disorders of consciousness based only on behavioral examinations. The increasing use of neuroimaging techniques allows improving clinical characterization of these patients. Recent neuroimaging studies using positron emission tomography, functional magnetic resonance imaging, electroencephalography and transcranial magnetic stimulation can help assess diagnosis, prognosis, and therapeutic treatment. These techniques, using resting state, passive and active paradigms, also highlight possible dissociations between consciousness and responsiveness, and are facilitating a more accurate understanding of brain function in this challenging population.

Keywords: Coma; EEG; PET scan; fMRI; minimally conscious state; neuroimaging; unresponsive wakefulness syndrome.

Fig. (1)

Nosology and evolution after a severe brain injury. UWS, unresponsive wakefulness syndrome; MCS, minimally conscious state. Adapted from [137].

Fig. (2)

Neuroimaging assessments in two patients behaviorally diagnosed as UWS. The patient on the left presents the typical pattern of UWS (i.e., low brain metabolism as shown in blue with FDG-PET, no resting state default mode network, severe atrophy of the white matter tracts as shown with DTI, and no brain activation during motor and spatial imagery tasks). The patient on the right presents a pattern not compatible with UWS, and should hence be diagnosed as MCS*. FDG-PET: fluorodesoxyglucose-positron emission tomography, fMRI: functional magnetic resonance imaging, here the resting state is the default mode network. DTI: diffusion tensor imaging. Taken from [14].

Fig. (3)

Glucose metabolism at rest in minimally conscious state (MCS) and in unresponsive wakefulness syndrome (VS/UWS). Blue represents areas with low metabolism and red represents areas with preserved metabolism when compared to healthy participants. Adapted from [27].

Fig. (4)

Resting state connectivity networks across healthy participants, patients in minimally conscious state (MCS), unresponsive wakefulness syndrome (UWS) and coma. For each network, a decrease is observed as a function of the level of consciousness. Taken from [64].

Fig. (5)

TMS-EEG Discriminates Between UWS and MCS. A. Descriptive brain responses to TMS in a UWS patient who evolved to MCS and to EMCS. Response under the TMS stimulation (top figure, black trace) and the following spreading of the activity in the brain (colors represent the location of the brain areas). White cross displays the site of the TMS stimulation (parietal cortex). The behavioral recovery was assessed with the Coma Recovery Scale-Revised (CRS-R). B. Quantitative brain responses to TMS in UWS, MCS, emergence of MCS and locked-in patients.The perturbational complexity index (PCI) progressively increases from UWS to MCS and exit MCS. PCI attains levels of healthy awake participants in locked-in patients whereas UWS show similar value as non-rapid eye movement sleep (NREM) and anesthesia in healthy participants. The threshold for consciousness is 0.31. Adapted from [112, 114].