A twitch of consciousness: defining the boundaries of vegetative and minimally conscious states.

Some patients awaken from their coma but only show reflex motor activity. This condition of wakeful (eyes open) unawareness is called the vegetative state. In 2002, a new clinical entity coined ‘‘minimally conscious state’’ defined patients who show more than reflex responsiveness but remain unable to communicate their thoughts and feelings. Emergence from the minimally conscious state is defined by functional recovery of verbal or nonverbal communication. Our empirical medical definitions aim to propose clearcut borders separating disorders of consciousness such as coma, vegetative state and minimally conscious state but clinical reality shows that these boundaries can often be fuzzy (fig 1). Recent clinical, electrophysiological and neuroimaging studies are shedding light on these challenging limits of consciousness encountered following severe acute brain damage. At the patient’s bedside, it is very challenging to differentiate reflex or automatic motor behaviour from movements indicating signs of consciousness, and hence some minimally conscious patients might be misdiagnosed as being vegetative. For some motor responses (eg, blinking to visual threat, brief fixation, normal flexion response to pain, etc) it remains unclear whether they truly are voluntary or willed because we lack convincing scientific evidence. We also lack consensus on how to practically assess some of these behavioural responses. For example, there is no agreement on what stimulus to employ in the assessment of visual pursuit movements— often one of the first clinical signs heralding the transition from the vegetative to the minimally conscious state. Vanhaudenhuyse and colleagues recently studied visual pursuit in 51 post-comatose patients comparing eye tracking of a moving object, person or mirror. It was shown that more than a fifth of the minimally conscious patients with visual pursuit only tracked when studied by means of a moving mirror and not when studied by means of a moving object (ie, the stimulus most frequently used in our routine neurological examination) or by means of a moving person. Such behavioural studies permit improvement in the challenging behavioural assessment and diagnosis of severely brain damaged patients. At present, the clinical examination remains the gold standard in defining the boundaries of disorders of consciousness. However, similar to the role of confirmatory para-clinical tests in brain death, validated objective markers of consciousness could improve our diagnosis of vegetative and minimally conscious states. In this issue, Bekinschtein and colleagues investigated command following (ie, ‘‘move your hand’’) while recording EMG activity in eight patients with the clinical diagnosis of the vegetative state (only patients with preserved withdrawal reflex and preserved auditory evoked potentials were included) (see page 826). In one such patient (studied 3 months after a traumatic brain injury and with only mild cerebral atrophy on MRI), significant command related sub-behavioural thresholdEMGchangesweredemonstrated. This finding indicates that the patient understood the task (no EMG changes were seen when a ‘‘do not move’’ command was presented) and repeatedly performed the task during a sustained period of time(ie,30 s).Hence,thereportedpatient,clinicallydiagnosedasvegetative,wasconscious. The proposed methodology is comparable—albeit much simpler, cheaper and portable—to the functional MRI methodology validated by Boly et al measuring blood oxygen level dependent cerebral activation in non-communicative patients. Using this functional MRI technique, Owen et al objectively showed signs of consciousness in a patient (studied 5 months after trauma) with the diagnosis of the vegetative state. These studies are clinically and ethically important, as the careful and controlled complimentary examinations changed the patient’s bedside diagnosis. The next challenge will be to adapt this technology such that it permits the patient to communicate his or her views and feelings (ie, thought translation devices or brain computer interfaces). The patient reported by Bekinschtein and colleagues recovered brief fixation and unintelligible vocalisation but failed to show any functional communication at the time of writing (12 months post-injury). Such behaviourally unresponsive patients, only showing identifiable signs of consciousness by means of sophisticated electrophysiological or neuroimaging techniques, will challenge our current standards for care and end of life decision making paradigms. It should, however, be emphasised that the reported patients suffered a traumatic brain injury and were studied within 6 months after injury. 5 Convincing signs of consciousness have so far never been reported in the post-anoxic vegetative state. In addition to the boundaries defining emergence from the vegetative state, the upper boundaries defining minimally conscious patients have been challenged. Recently, Nakase-Richardson and colleagues studied the clinical criteria for emergence from the minimally conscious state—that is, functional interactive communication—operationally defined as accurate yes/no responses to six of six situational orientation questions on two consecutive evaluations. Having performed standardised cognitive testing in 336 responsive patients recovering from traumatic brain injury, the authors conclude that these criteria might be too