Preserved consciousness in vegetative and minimal conscious states: systematic review and meta-analysis

Abstract

Active, passive and resting state paradigms using functional MRI (fMRI) or EEG may reveal consciousness in the vegetative (VS) and the minimal conscious state (MCS). A meta-analysis was performed to assess the prevalence of preserved consciousness in VS and MCS as revealed by fMRI and EEG, including command following (active paradigms), cortical functional connectivity elicited by external stimuli (passive paradigms) and default mode networks (resting state). Studies were selected from multiple indexing databases until February 2015 and evaluated using the Quality Assessment of Diagnostic Accuracy Studies-2. 37 studies were identified, including 1041 patients (mean age 43 years, range 16-89; male/female 2.1:1; 39.5% traumatic brain injuries). MCS patients were more likely than VS patients to follow commands during active paradigms (32% vs 14%; OR 2.85 (95% CI 1.90 to 4.27; p<0.0001)) and to show preserved functional cortical connectivity during passive paradigms (55% vs 26%; OR 3.53 (95% CI 2.49 to 4.99; p<0.0001)). Passive paradigms suggested preserved consciousness more often than active paradigms (38% vs 24%; OR 1.98 (95% CI 1.54 to 2.54; p<0.0001)). Data on resting state paradigms were insufficient for statistical evaluation. In conclusion, active paradigms may underestimate the degree of consciousness as compared to passive paradigms. While MCS patients show signs of preserved consciousness more frequently in both paradigms, roughly 15% of patients with a clinical diagnosis of VS are able to follow commands by modifying their brain activity. However, there remain important limitations at the single-subject level; for example, patients from both categories may show command following despite negative passive paradigms.

Somatosensory attention identifies both overt and covert awareness in disorders of consciousness

“…25 There have also been reports of correlations between cognitive ERPs and behavioral markers of awareness, 14,24 as well as the prediction of recovery from DoC using cognitive ERPs. This step is important given that a recent meta-analysis estimates a 15% rate of covert awareness among patients diagnosed as in a VS. 27 Previous studies of the P300 in patients with DoC are likely to have included patients capable of covert command following, thus obscuring the relationship reported here. This step is important given that a recent meta-analysis estimates a 15% rate of covert awareness among patients diagnosed as in a VS. 27 Previous studies of the P300 in patients with DoC are likely to have included patients capable of covert command following, thus obscuring the relationship reported here.…”

“…8,19 Researchers have developed assessments of brain function to place a patient along a hierarchy of increasingly complex attentional information processing. 27 Similarly, most studies of patients with DoC employ auditory stimulation because many patients lack oculomotor control; however, this tendency limits the characterization of a patient's sensory abilities to the auditory domain. 26 These inconsistencies may have occurred because multimodal assessments were not used to identify patients in a nonbehavioral MCS.…”

Vegetative State: Difficulty in Identifying Consciousness and Predicting Outcome

“…В настоящее время для изучения функционального состояния головного мозга при проведении МРТ у па-циентов в ВС и СМС используется три вида парадигм: состояние покоя, пассивная и активная парадигмы [25]. Наиболее удобным для изучения является состояние покоя, когда пациенту не подается никаких стимулов.…”

“…D. Kondziella и соавт. [25], проведя метаанализ 36 работ по изучению «состояния покоя» при выполнении фМРТ у больных в ВС и СМС, пришли к вы-воду, что у всех пациентов отмечается снижение активно-сти в структурах «сети пассивного режима работы мозга», однако в некоторых случаях степень вовлечения в работу сети предклинья позволяет провести дифференциальный диагноз между ВС и СМС, т.к. у пациентов в ВС актив-ность предклинья выражена меньше, чем у пациентов в СМС.…”

“…Метаанализ специфичности и чувствительности в выявлении сознания активной и пассивной парадигм показал, что из 292 пациентов, соответствующих крите-риям диагноза ВС, 42 (14,4%), по данным фМРТ, имели признаки сознания: активность мозга этих пациентов менялась в соответствии с предложенным стимулом [25]. T.A.…”