Language assessment in patients in a “vegetative state”: the key to diagnostic errors?

"Paul" had a heart attack and his brain lacked oxygen for too long. After several resuscitations and a week in a coma, he finally opened his eyes again… but doesn't always seem present. Doctors say he is still unconscious, in an "unresponsive awake state" (vegetative state) - he keeps his eyes open, but does not move his arm or shake his hand when asked. This trying sequence, many families have experienced it. With always the same nagging question: will the patient become conscious again?

In recent decades, intensive care medicine has become particularly effective, to the point of allowing many people who have suffered a serious brain injury to “come back to life”. However, some will never recover their initial state of consciousness: they will remain in a so-called altered state, characterized by a deterioration in their connection to their environment, but also to themselves (their perceptions, emotions, etc.). ). For from the "inert" state to complete awakening, there is a wide range of different states of consciousness, often poorly known to the general public but which neuroscience is working to better define.

Thus, after an episode of coma proper (where the eyes remain closed) lasting between one hour and four weeks, several stages of recovery and intermediate states of consciousness normally follow until "emergence"... but which can last and become chronicles:

• Unresponsive awake state (formerly called vegetative state and renamed in 2010 to better describe the symptoms): the patient opens his eyes but shows no sign of consciousness;
• State of minimal “minus” consciousness: reappearance of signs of consciousness such as oriented behaviors, visual pursuit/fixation, or localization of painful stimuli;
• State of minimal “plus” consciousness: reappearance of linguistic signs of consciousness (response to verbal command, verbalization of words, attempts at communication);
• Emergence: as soon as the patient is able to communicate using a yes/no code or to use everyday objects adequately, he is considered to have emerged from the state of minimal consciousness.

Diagnosis of the state of consciousness following brain damage: coma, unresponsive state of wakefulness (vegetative state), state of minimal consciousness minus, state of minimal consciousness plus and emergence.
Wisłowska et al. (2017). Night and day variations of sleep in patients with disorders of consciousness, Author provided

It is also crucial to be able to distinguish these states of altered consciousness from a syndrome of confinement or “locked-in”. This syndrome also results from a serious lesion in the brain, but localized at the level of the brainstem. This results in paralysis of the limbs, head and face, while consciousness and cognition can be preserved. Communicating then most often involves eye movements.

How to assess states of altered consciousness?

These altered states of consciousness remain difficult to diagnose, in particular because there is not yet a fully recognized link between the processes occurring in the neural circuits and the state of consciousness. Cerebral imaging therefore does not (yet) allow an optimal diagnosis of unresponsive arousal or minimal state of consciousness.

The method which remains the most recognized currently is the evaluation at the bedside of patients thanks to a standardized and validated scale.

The scale Glasgow Coma Scale is the best known and the most studied for its prognostic value. However, it does not allow the diagnosis of a state of consciousness because it does not assess the most frequent signs of the minimal state of consciousness (in particular visual fixation/pursuit).

It is, however, the case of theComa Recovery Scale or Simplified scale of consciousness disorders (Simplified assessment of consciousness disorders), which make it possible to identify auditory, visual, motor and linguistic signs of consciousness. Without it, a diagnosis based on simple clinical observation would present about 40% errors.

But to be considered reliable, these assessments must be repeated. It is recommended to do them approx. five times in a fairly short period of time (eg two weeks). The risk of diagnostic errors would drop from 36% after a single evaluation to 5% after the fifth.

This difficulty in making a correct diagnosis based on behavioral assessments is partly related to patients' fluctuating level of arousal. In addition, they often present disorders associated with that of consciousness. For example, the extent of their lesions may imply the presence of visual disturbances that interfere with the assessment of visual fixations/pursuits. In the case of "palpebral ptosis" (inability to raise the eyelids), the clinician must take care to carry out this visual assessment by opening the patient's eyes himself, at the risk otherwise of wrongly considering him as non-responsive.

A new language approach

“Paul”, to use our initial character, does he understand his relatives when they talk to him? This is probably one of the first questions asked of the nursing staff by the families of a patient who wakes up from a coma. And for good reason: the ability to understand language and to be understood is an essential element of the patient's quality of life. It allows him not only to connect to his environment (to his loved ones), but also to express his needs and desires.

The assessment of language skills by speech therapists is thus a key step in the establishment of communication with the patient, on which health professionals can rely in order to provide the best possible support.

However, the state of consciousness of "Paul" could be underestimated if he no longer understands verbal language, if the language regions of his brain have been damaged too much by the absence of oxygen. Indeed, although conscious, he might not respond to commands simply because he does not understand them… How, then, can we determine whether these patients have language and/or consciousness disorders?

Ce aphasia problem (language disorder following brain injury) in the diagnosis of consciousness was brought to light several years ago. This study then showed that approximately 25% of aphasic but fully conscious patients (following a stroke) could be diagnosed as being in a minimally conscious state using theComa Recovery Scale : the real level of consciousness can therefore be seriously underestimated if the linguistic brain regions are affected by lesions.

All of these data underline the importance of improving the language assessment of patients awakening from a coma.

But how to assess the language skills of these patients, despite their visual, auditory and motor dysfunctions? Current research attempts to answer this question.

Help to limit misdiagnoses

Our recent systematic review of the literature mainly reports the use of electroencephalography (EEG) or magnetic resonance imaging (MRI) methods, which make it possible to measure the activity of brain regions usually related to language. These two techniques are complementary because if MRI makes it possible to better identify the cerebral regions activated by a task, it remains more expensive and difficult to set up than EEG.

Whether with one or the other of these techniques, two types of tasks can be carried out:

• On the one hand, passive listening tasks involve making patients hear various types of words or phrases. For example, we look at the difference in brain activity depending on whether the patient hears noise or verbal language. In the studies reported in our review, about 33% of patients considered to be awake unresponsive show such signs of language comprehension.

Passive tasks vs. active to identify language comprehension in patients awake from coma. The first are based on EEG and MRI and make it possible to assess cerebral activity in response to various language stimuli; the second measures the ability to respond to verbal commands, either behaviorally or via EEG and MRI.
Charlene Aubinet, Author provided

• On the other hand, there are more active tasks, in which the patient is asked to respond to a verbal command. When based on EEG and MRI, these tasks generally employ so-called motor imagery, prompting the patient to imagine themselves carrying out a particular activity. For example, the patient hears the command “imagine yourself walking around your house” or “imagine yourself playing tennis”. Mentally visualizing these actions should normally activate different brain regions: if the patient shows this type of activation, it can be deduced that he has responded to the command heard. About 20% of patients considered to be awake unresponsive manage to perform these tasks.

Le level of consciousness of these patients would therefore be misdiagnosed. Since they respond to commands, they are actually in a minimally conscious state – also referred to in this case as a minimally conscious state*.

One-third and one-fifth of awake unresponsive (ENR) patients respond to passive and active tasks, respectively. The more their level of consciousness increases, through the minimally conscious state (MCS) and until the emergence of the minimally conscious state (MCES), the more residual language abilities are observed in patients.
Charlene Aubinet, Author provided

The consequences of a misdiagnosis

These diagnostic errors can have a significant impact on prognosis and patient management.

Two concrete examples: the nursing staff will be more attentive to the pain treatment of a patient in a state of minimal consciousness compared to a non-responding patient, considered to have altered pain perception. More importantly, end-of-life decisions will be addressed more often in the case of a unresponsive awake patient.

It therefore seems crucial to improve the evaluation of language in order to better target the real state of consciousness of these patients who have survived a coma.

Although neuroimaging examinations can provide essential information to healthcare professionals, they do not always have access to EEG and MRI techniques. This is why new efforts are being made to develop language assessment tests on awakening from coma.

In particular, the BERA tool (brief evaluation of receptive aphasia) Is currently being validated. It consists of presenting pairs of images to the patient, who must stare at the one that corresponds to the word or phrase he hears. Thanks to this test, which will soon also be adapted with an eye tracking device (objective measurement of eye movement), we hope to provide a new tool that is easy to access and inexpensive for all clinicians awake from a coma.

Many advances are therefore still to be expected in this field of clinical research. The methods of evaluation (but also of rehabilitation) will have to evolve in parallel with those of medicine in intensive care, in order to help patients, like “Paul”, to be able to communicate again.

For health professionals wishing to learn more, here is the link to access the material of our new diagnostic scales.

Charlene Aubinet, FNRS researcher, neuropsychologist and speech therapist, university of Liege et Olivia Gosseries, Co-director of the Coma Science Group, FNRS qualified researcher, Neuropsychologist, university of Liege

This article is republished from The Conversation under Creative Commons license. Read theoriginal article.