A multiple case study investigating the sub-categorization of the minimally conscious state

The minimally conscious state (MCS) was sub-categorized in MCS+ and MCS- based on language-related behaviors (i.e., command-following, intelligible verbalization or intentional communication). Due to pronosis implications, it is important to detect signs of MCS+ and evaluate patients’ likelihood to recover such behaviors. We here aim to describe behavioral and neuroimaging data of severe brain-injured patients who evolved from MCS- to MCS+. Four patients were thus assessed at two time points by means of repeated Coma Recovery Scale-Revised. During their first week of assessments, they were diagnosed as MCS-. They later recovered language-related behaviors (i.e., MCS+), when reassessed during their second week of evaluations. All patients underwent a positron emission tomography (PET-scan) and magnetic resonance imaging (including voxel-based morphometry – VBM) exams during both weeks of assessments. We here compared the neuroimaging differences between the two exams in these four patients. PET-scan results showed that all patients presented partial recovery of metabolism in temporal lobules, reflecting compensation either from left-sided language areas or from their contralateral regions. VBM results showed that two patients presented a significant increase of grey matter volume, particularly concerning either bilateral frontal areas or the left caudate, which was related to memory, learning and language abilities. The other two patients did not show difference in grey matter structure between MCS- and MCS+. We conclude that the clinical evolution of patients from MCS- to MCS+ suggests the reappearance of language-based behavioral signs, but also the partial recovery of metabolism and grey matter structure in cerebral regions that are involved in language processing. All patients recovered signs of MCS+ at an advance chronic stage. These neuroimaging results highlight the remaining neuroplasticity in chronic MCS.