Clinical Assessment Procedure
The diagnosis of the vegetative and minimally conscious state is currently made on the basis of the patients clinical history supported by detailed behavioural observations. The clinical assessment procedure does NOT include functional brain imaging or cognitive electrophysiology as standard.
The Royal College of Physicians of the United Kingdom (2003) have produced guidance on the diagnosis and management procedure for vegetative state. Similarly an international working group have produced diagnostic criteria for the minimally conscious state (Giacino et al., 2002). However, no National or International standard currently exists for the assessment of these conditions and practices vary widely between centres. The information below reflects many of the recommendations from the above working groups together with the personal opinion and experience of Martin Coleman, Impaired Consciousness Research Group, University of Cambridge.
Preconditions for diagnosis
The working group guidelines both set out clear preconditions before a diagnosis can be considered:
1. The cause of the condition should be established.
2. The possibility that the persisting effects of sedative, anaesthetic or neuromuscular blocking drugs must be excluded as the continuing cause of reduced conscious level.
3. The possibility that there is a treatable cause – structural or metabolic should be excluded.
Clinical Features
Vegetative state
The vegetative state is commonly described as a condition of wakefulness without awareness. A person in a vegetative state will open their eyes and show sleep-wake cycles, but they do not show any evidence of awareness of themselves or environment. The vegetative state is distinguished in part from the minimally conscious state by (1) no evidence of purposeful, sustained or reproducible response to visual, auditory, tactile or noxious stimulus, (2) no evidence of awareness of self or environment, and (3) no evidence of language comprehension or expression. Unlike patients in coma a person in the vegetative state demonstrates evidence of eye opening and sleep/wake cycles. Patient's may have preserved or partially preserved reflexes, but exhibit no purposeful behaviour. The vegetative state reflects a spectrum of impairment rather than one condition. At the lowest boundary a patient may demonstrate limited periods of eye opening and partially preserved reflexes, such as blinking to a loud noise. At the upper boundary a patient may exhibit prolonged periods of eye opening, fleeting fixation upon people or objects (less than 5 seconds) and preservation of more complex reflex responses, such as withdrawal to tactile stimulation. In both cases the patient demonstrates no evidence of awareness of themselves or environment.
A person can be described as in a Permanent Vegetative State (or more accurately to have a lower probability of further recovery), if at 12 months post traumatic (i.e., road traffic accident) or at 6 months post non-traumatic (i.e., cardiac arrest) they continue to show no awareness of self or environment during rigorous multidisciplinary assessment.
Minimally conscious state
The term minimally conscious state describes a person who shows intermittent, but clear evidence of awareness of themselves or their environment. This condition describes a broad spectrum of purposeful behaviour. At the lowest boundary a person might demonstrate visual fixation or pursuit of a person or object through their visual field. At the highest boundary the person might intermittently, but reproducibly, respond to command using movement or speech. Critically the minimally conscious state is distinguished from the vegetative by (1) often inconsistent, but crucially reproducible evidence of awareness of self or environment, and /or (2) purposeful and reproducible responses to sensory stimuli. Just like vegetative patients they also demonstrate evidence of eye opening and sleep wake cycles, but basic reflexes are typically diminished, replaced by cortically mediated purposeful behaviour.
Assessment
The diagnosis of the vegetative or minimally conscious state should be made with great care. The Royal College of Physicians suggests that this process should be undertaken by two independent and highly experienced doctors. They should take into account the views and observations of the multidisciplinary team working with the patient and the patients carers and relatives. There is strong evidence that the vegetative state has previously been diagnosed in error (Andrews et al., 1996; Childs et al, 1993). Misdiagnosis has been attributed to confusion about the definitions of these conditions, inadequate observation, failure to consult those who see the patient most and critically the inherent difficulty of detecting signs of awareness in patients with significant perceptual and motor impairments. In order to avoid these difficulties the following steps are recommended:
Step 1: Review Clinical History
It is vital that an accurate and detailed clinical history for the patient, including premorbid history is obtained. This information forms the basis of the diagnosis. There should be an identified cause of the condition which is recognised to be capable of resulting in the vegetative or minimally conscious state. Detailed information concerning the circumstances of the accident, duration and on the scene medical care are vitally important. Initial and repeated computed tomography or magnetic resonance imaging data also provide valuable information to establish the cause of the condition. However, note that these conditions are defined by the behaviours the patient exhibits and not a uniform pathological presentation. The vegetative and minimally conscious state can arise following a traumatic brain injury, infection, metabolic disturbance, vascular and degenerative disease. The injuries sustained by patients are particularly heterogeneous. Post mortem work has suggested three categories of injury: (1) injuries to the brainstem and subcortical structures mediating wakefulness, with a relatively intact cerebral cortex, (2) diffuse damage to the cerebral cortex, mediating awareness, with a relatively intact brainstem, and (3) injuries involving both these areas of the brain.
Review of the patients clinical history provides vital information pertinent to the differential diagnosis, especially exclusion of the locked-in syndrome. This condition typically arises from an insult to the ventral pons, most commonly an infarct, haemorrhage or trauma. The condition can also arise from extensive bilateral destruction of the corticobulbar and corticospinal tracts in the cerebral peduncles. The basic characteristics of this condition are quadriplegia and anarthria with preservation of consciousness. Patients generally retain vertical eye movement, facilitating non-verbal communication. This presentation is generally referred to as the classic presentation. However, there are other variants (a) incomplete – where in addition to the classic presentation a person retains remnants of voluntary movement other than vertical eye movement, and (2) total – where the person is totally immobile and unable to perform vertical eye movement, but retains full consciousness. The locked-in syndrome can be hard to diagnose as some patients emerge from coma into locked-in syndrome after a variable delay and often superficially resemble patients in a vegetative state. In the acute period vigilance and eye movement may be inconsistent, limited and easily exhausted. It has been shown that on average it takes 2.5 months after the injury before a diagnosis of locked-in syndrome is confirmed. Indeed, the Royal College of Physician guidelines suggest there should be no rush to make a diagnosis and instead careful and repeated observations by the multidisciplinary team should continue over a prolonged period.
Step 2: Excluding other factors
Many medications in addition to anaesthetic and neuromuscular blocking drugs have sedative side effects. The examining doctor will make every effort to exclude the possibility of these drugs underlying the reduced consciousness level. Similarly before detailed behavioural observations are performed, the doctor will review and where possible reduce dosage or wean a patient off certain medications. This will facilitate the best possible opportunity for the patient to respond to command.
Step 3: Neurological examination
The examining doctor will perform a detailed neurological examination of the patient. This provides valuable input to the subsequent interpretation of behavioural assessments. For instance, the presence of a third nerve palsy, dysconjugate eye movement and/or ptosis have implications for the subsequent interpretation of behaviours exhibited by the patient in response to visual stimulation. Similarly, muscle wastage and tendon shortening have implications for the range of movement the patient can undertake and may severely impede their ability to respond to command. Third nerve palsy, manifest as dysconjugate eye movement or inability to move eyelids (ptosis), prevents the assessment of key behavioural markers of awareness, such visual pursuit.
Step 4: Nutrition and hydration
Nutrition and hydration are typically provided via a percutaneous gastrostomy (PEG). In order for the patient to have the best possible opportunity to respond to sensory and cognitive stimulation it is vitally important that their nutritional and hydration requirements are ensured.
Step 5: Positioning and posture
One of the greatest influences on a patients ability to respond to command is their position and posture. A patient lying in bed, regularly rolled onto their side to avoid pressure sores or surrounded by pillows is likely to have a compromised visual field and range of movement. It is essential prior to formal behavioural assessment that any patient is assessed by the occupational and physio-therapy team to ensure optimal positioning and posture. Ideally a patient should be positioned in a seated, upright position, preferably in a wheel chair. The patient should have adequate support, optimised range of movement and an unimpaired visual field. This will ensure the patient has the best opportunity to respond to stimulation. It will also facilitate a greater range of spontaneous behaviours.
Step 6: Respiration and swallowing
A considerable number of patients have a tracheostomy, which depending upon the type, may mask the possibility of vocalisation or a response to smell. A tracheostomy tube is held firmly in place and as a result it can restrict the amount of larnygeal elevation needed to ensure complete closure of the lower respiratory tract during swallowing. An over-inflated cuff can also anchor the larynx firmly in the neck and contribute towards aspiration. Air is no longer drawn through the nasal cavity and, as a result, the sense of smell is greatly reduced or even absent.
Step 7: Behavioural assessment techniques
A number of behavioural assessment scales specifically for this patient group have been validated. Each have their merits and limitations, but the most commonly used are the sensory modality assessment and rehabilitation technique (SMART) and the JFK Coma Recovery Scale (CRS).
SMART
The SMART is a 10 session assessment process that consists of measuring the patient's resting behaviour and behaviour in response to different stimuli. Each session consists of measuring the patients spontaneous behaviour for 10 minutes in a non-stimulating environment. This is immediately followed by an assessment of behavioural responses (sensory and cognitive) to different stimuli in the five senses (visual, auditory, tactile, olfactory and gustatory), as well as motor function, communication and level of wakefulness. A five-point hierarchical scoring system categories responses from (1) no response, (2) reflex response, (3) withdrawal response, (4) localising response, and (5) differentiating response.
The SMART is a well designed and thorough assessment of the patients behavioural portfolio. Like the CRS it looks at a patients response in each sensory modality, carefully applying controlled stimuli and differentiating between reflex and purposeful responses. The scale also utilises important information gleaned from spontaneous behaviours and listens to what family members have observed. The great strength is that it is applied over a prolonged period of time and different times of the day. This ensures the examiner really gets to know the patient. The SMART scale directly links to the diagnostic distinction between the vegetative and minimally conscious states. The SMART is also the only assessment scale to incorporate treatment planning and assessment. Indeed, after the initial 10 session assessment, a treatment block is designed, applied and the effects upon behaviour assessed again using the SMART.
In order to use the SMART scale the developers run a one-week course twice a year at the Royal Hospital for Neurodisability in London. This course aims to ensure everyone using the SMART is sufficiently knowledgeable and experienced in order to maintain a quality of assessment across centres and also reduce the rate of misdiagnosis arising from application by inexperienced staff.
More information about the SMART course can be found here [link]
Gill-Thwaites H & Munday R. The sensory modality assessment and rehabilitation technique (SMART): a valid and reliable assessment for vegetative and minimally conscious state patients. Brain Injury, 2004; 18(12): 1255-1269.
CRS
The CRS was originally developed to more fully characterise and monitor patients functioning at level I (generalised response) to level IV (confused-agitated response) on the Rancho Los Amigos Levels of Cognitive Functioning Scale. The CRS is comprised of six subscales addressing auditory, visual, motor, oromotor, communication and arousal processes with the individual subscale items ordered in a hierarchical manner. The lowest item on each subscale represents reflexive activity while the highest items represent cognitively mediated behaviours. The CRS uses slightly different methodology to the SMART and does not record spontaneous behaviour or family observations. Nevertheless it does link directly to the diagnostic distinction between the vegetative and minimally conscious states.
Giacino JT, Kalmar K, Whyte J. The JFK Coma Recovery Scale-Revised: measurement characteristics and diagnostic utility. Archives of Physical Medicine and Rehabilitation, 2004; 85(12): 2020-2029.
More information about the CRS can be found here [link]
Step 8: The behavioural assessment procedure
Once medication, posture, positioning and nutrition have been addressed and optimised, implementation of the above behavioural assessment scales can begin. Assessments should take place at different times of the day and in different positions (sitting, standing, lying) over a prolonged period. The environment in which the patient is assessed should be controlled as much as possible. Hence, testing should be conducted in a quite room, free of extraneous noise and disturbance with only the assessor(s) present. The room should be neutral in colour and the patient should be positioned in the centre of the room with their back to the window. In essence creating a quite environment free from distraction and thus optimised for determining whether the patient is responding specifically to the assessment stimuli.
The SMART scale begins with a 10 minute period of observation during which all spontaneous behaviours are recorded. This is repeated at the beginning of all 10 sessions, with each assessment eventually collated to form the overall report. Watching a patient at rest can often reveal vitally important information. For example, visual fixation, localisation or object manipulation. Observations at rest also tell you a lot about the wakefulness/arousal level of the patient.
The next stage is to record the patients response to specific stimuli applied in the visual, auditory, tactile, olfactory and gustatory modality. The SMART and CRS apply similar stimuli and specify the method of application, which is designed to exclude extraneous variables, such as the assessor standing in the field of view when determining if the subject localises to a sound presented from the left or right. Assessment of the patients response to stimuli in each modality follows a hierarchical pattern, moving from determining whether the patient demonstrates a basic reflex response to light to purposeful responses. For example, the visual modality begins with determining what the patient does when presented with a bright light. Does the patient demonstrate (1) no response, (2) a startle response, (3) blinking, (4) a single blink followed by eye closure, or (5) orientation and fixation upon the stimuli? The stimuli then progressively become more complicated. For instance, the patients response is then assessed to a visual stimulus moving in the line of vision or response to written instructions. At each stage the CRS and SMART specify how the stimuli should be presented and where the assessor should stand. Stimuli are typically repeated twice and the assessor should carefully document the patients response. It is recommended that each session begins with a different modality and that all hierarchical elements of the scales are applied, regardless of whether the patient initially responds or not. For example, basic reflex responses typically diminish for patients in the minimally conscious state and are replaced by purposeful, consciously mediated responses. Hence, initially the patient may show no response to a bright light. However, move up the scale and apply more complex stimuli, such as a written instruction and the patient responds purposefully.
These assessments should be applied repeatedly at different times of the day over several weeks in order to reveal the true behavioural pattern of the patient. Interpretation based on a single session is totally inappropriate for several reasons. Firstly, it is impossible to document the full behavioural portfolio of a patient, the assessor does not know what that person is like at a different time of day, in response to other people or in a different position, i.e., supine versus seated. Through repeated observation these confounding variables can be largely overcome.
Step 9: Collecting the observations of the family and carers
In addition to the observations made during the formal CRS and SMART assessments, it is vital that the observations of patients family and immediate multidisciplinary care team are also collected. Family members spend the longest period with the patient and can often highlight important behaviours for the assessor to investigate in a controlled environment. Similarly, important behaviours are often exhibited by patients during interventions and the multidisciplinary care team are vital sources of information for the assessor.
The SMART scale formally incorporates this information through several pre-assessment informs, which are used to investigate behaviours highlighted by the family in a controlled environment.
Step 10: Collating information
After prolonged behavioural assessment, all the information recorded on the SMART or CRS is put together with the patients detailed clinical history and other sources of medical information, such as CT scan. In the SMART this information is used to plan a treatment block, which focuses upon one or more consistent behaviours and tries to facilitate more purposeful/communication responses using that behaviour. A treatment block may last several weeks, after which the SMART assessment is repeatedly acquired for a further 10 sessions to evaluate progress. After the second assessment a second treatment block may be instigated and the SMART assessment repeated.
Step 11: Diagnosis
Having established the cause of the syndrome, excluded potential contributing factors such as the effects of sedation or neuromuscular blockade and treated any reversible cause, the two doctors making the assessment will separately consider the results of all investigations performed over a prolonged period. The Royal College of Physicians guidelines states that there is no rush for such decisions to be made. Rehabilitation interventions should be instigated on the basis of assessments such as the SMART and recovery over time should be monitored. Indeed, within the time thresholds for decisions about prognosis (12 months post traumatic and 6 months post non-traumatic) there is good argument to label patients as having impaired consciousness following brain injury, rather than vegetative state. In practice once a term like vegetative state is used, it often carries, regardless of the patients true behavioural presentation. It is therefore wise to avoid the use of this term until prognostic decisions are made at 12 or 6 month thresholds. The proceeding time period is often one of great change and potential for recovery, with about 20% of traumatically brain injured patients regaining consciousness within the first six months. A diagnosis made too early, without provision for monitoring change over time, is therefore prone to errors.
The formal thresholds for decisions about long-term prognosis and permanent vegetative state are 12 months post traumatic brain injury and 6 months post non-traumatic brain injury (this later threshold is 3 months in the USA). Although further recovery can not be ruled out and several incredible recoveries up to 10 years post-ictus have been published, the chances of recovery generally diminish with time after severe brain injury. Hence, the term 'permanent' is misleading. It should really say the possibility of further recovery is less with time.
Step 12: Other sources of information
1. Functional Brain Imaging
At present functional brain imaging remains confined to the use of a few specialist research units. Although insufficient population data exists to convene an expert panel to appraise the use of functional imaging with this patient group, there are already many reports highlighting the potential utility of this equipment. It is true only a small number of patients have been investigated with these techniques, but where carefully designed cognitive paradigms have been employed, the potential to circumvent the behavioural assessment reliance upon overt motor activity and the subjective nature of interpretation, have been striking. Brain imaging certainly has the potential to reveal covert aspects of key cognitive processes and even awareness in the absence of behavioural markers. However, it is probably appropriate for such investigations to remain confined to a few specialist centres, rather than rolled out to more general care settings. This is necessary to guard against the use of poorly designed paradigms and incorrect interpretation. For instance, increased blood flow in response to hearing your mothers voice, versus scanner noise, does not imply the patient recognised the mothers voice or was aware of doing so. Brain activation in one condition and not in another does not necessarily reveal task specific correlates. Similarly, the absence of activation during one task does not imply the person was unable to perform the task. False negative responses are widely reported in healthy volunteers and therefore only positive findings can be interpreted. Hence, while carefully designed and interpreted functional brain imaging paradigms offer valuable additional information to the clinical assessment, they should only be used in specialist research units with the experience and knowledge to perform and interpret this data.
2. Cognitive electrophysiology
Probably at a greater pace than functional brain imaging, cognitive electrophysiology has for many years demonstrated considerable potential for revealing covert aspects of key cognitive processes, in addition to providing prognostic information. Electrophysiology has many benefits over brain imaging in terms of assessing patients at the bedside with relatively inexpensive equipment. However, cognitive electrophysiology is not performed as standard at the present time. This is partly due to the fact that many clinical neurophysiology departments in district general hospitals do not routinely perform cognitive paradigms and many clinical EEG systems only offer basic P300 oddball paradigms.
References
Royal College of Physicians. The vegetative state: guidance on diagnosis and management [Report of a working party]. Royal College of Physicians, London, 2003.
Multi-Society Task Force on the Persistent Vegetative State. Medical aspects of a persistent vegetative state. New England Journal of Medicine, 1994; 330: 499-508, 572-579.
Giacino JT, Ashwal SA, Childs N, Cranford R, Jennett B, Katz DI, Kelly J, Rosenberg J, Whyte J, Zafonte R. & Zasler N. The minimally conscious state: Definition and diagnostic criteria. Neurology, 2002; 58: 349-353.
Jennett B. The vegetative state: medical facts, ethical and legal dilemmas. Cambridge University Press, Cambridge, 2002.
Gill-Thwaites H & Munday R. The sensory modality assessment and rehabilitation technique (SMART): a valid and reliable assessment for vegetative and minimally conscious state patients. Brain Injury, 2004; 18(12): 1255-1269.
Giacino JT, Kalmar K, Whyte J. The JFK Coma Recovery Scale-Revised: measurement characteristics and diagnostic utility. Archives of Physical Medicine and Rehabilitation, 2004; 85(12): 2020-2029.
Coleman MR. The assessment and rehabilitation of vegetative and minimally conscious patients. Psychology Press, Hove, 2005.
Andrews K, Murphy L, Munday R. & Littlewood C. (1996). Misdiagnosis of the vegetative state: Retrospective study in a rehabilitation unit. British Medical Journal, 1996; 313: 13-16.
Childs NL, Mercer WN. & Childs HW. Accuracy of diagnosis of persistent vegetative state. New England Journal of Medicine, 1993; 43(8): 1465-1467.