Can patients in vegetative state experience pain and have conscious awareness?

The diagnosis of prolonged disorders of consciousness remains problematic despite the available guidelines; misdiagnosis between the vegetative state (VS) and minimally conscious state (MCS) is estimated to hover around 40%. Neurologists are also confronted with many unresolved issues that vex both the patient’s family and the health team, prominent among which are pain, affective responsiveness, and conscious awareness. Do patients in VS experience pain? Are patients inMCS capable of some cognition? In this issue of Neurology®, Yu et al., studied 44 patients in a VS, or unresponsive wakefulness syndrome, for whom recordings were played of human voices expressing pain and suffering. In 24 of them, fMRI detected hemodynamic activation of brain structures that extended beyond the primary sensory areas and were virtually identical to those of healthy subjects. The authors suggested that these patients can feel their own pain and that some of them also experience the pain of others in the absence of conscious awareness. Additionally, 4 patients also responded to imagery instructions, such as imaging tasks of playing tennis or moving around the rooms of their home, suggesting that activation of cortical structures, as demonstrated by fMRI, PET, or by cognitive evoked responses, can indicate conscious awareness, as suggested by others previously. The present study’s findings indicate that brain mechanisms underlying affective consciousness can survive even very severe lesions that make impossible higher conscious functions such as attention, working memory, or language comprehension. However, these studies raise issues that require careful evaluation. Are images of increased blood oxygen level–dependent signal (fMRI) or oxygen/glucose uptake (PET) equivalent to conscious perception, or indicative of awareness, or are they simply document-retained modular function in the absence of the integrative processes necessary for consciousness? For instance, activation of the striate cortex may be preserved in patients who have become cortically blind after a stroke that destroyed connections with other cortical regions; the striate cortex module is no longer integrated with other cortical structures necessary for visual perception. Are the responses measured in this study evidence of conscious emotional perception of pain and suffering, or simply autonomic reflexes? Yu et al. correctly acknowledge they cannot answer these pivotal questions. There are some limitations of the study, mainly a lack of clinical neurologic details and the failure to differentiate clinically between VS and MCS; placing everyone under the classification of unresponsive wakefulness syndrome allows speculation that the patients who responded to “imagery” would represent, at a minimum, those with MCS. Neuroimaging measures are attractive because they are quantitative, but they are uncertain surrogates for something as complex as consciousness. Can neuroimaging studies truly differentiate patients with a sentient mind from patients with a body but without sentience—assuming we can define “sentience” in a manner acceptable to all? If functional imaging is the only reliable (if imperfect) method to provide evidence of cerebral integrative processing, does every patient in VS require an fMRI evaluation? Clearly, fMRIs are only available in selected centers and at present are mainly a research tool. Yet the ability of the clinician to differentiate between VS and MCS may be essential in the management and prognosis of patients, the allocation of resources, and the setting of health care policies. Luauté et al., in a study of 51 patients with prolonged disorders of consciousness, noted that “in contrast to patients in VS, a third of patients in MCS improved more than 1 year after coma onset.” Visual pursuit responses observed over multiple times were indicative of evolution from VS to MCS, suggesting the importance of multiple clinical observations. The foregoing suggests that we may need to update diagnostic and prognostic guidelines and conduct additional research to define and establish a more reliable boundary between VS and MCS. The ethical issues, the cost/benefit ratio, and the legal and popular perception of any new recommendations also need to be considered. Should repeated clinical evaluation prove inadequate to establish a diagnosis, could the scientific