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Home / Beyond mild, moderate and severe: A new way of classifying traumatic brain injuries
By Isobel Cory and Izzy Parker, Assistant Psychologists at Brainkind
Traumatic brain injury (TBI) is a common and complex medical condition that can result from falls, accidents, sports injuries, and other impacts to the head. Traditionally, clinicians have classified TBI severity using the Glasgow Coma Scale (GCS) [1]. However, this focuses mainly on the level of consciousness, without integrating objective biological or imaging data. As a result, it oversimplifies the wide range of injury effects and outcomes [2].
Recognising these issues, a new multidimensional framework has been developed by the US National Institutes of Health – National Institute of Neurological Disorders and Stroke (NIH-NINDS), with the aim of improving the characterisation of acute TBI. This framework incorporates clinical assessments, blood biomarkers, imaging findings, and individual modifiers to provide a more complete and personalised profile of a person’s injury [3].
As mentioned, the current classification of TBI relies mainly on the Glasgow Coma Scale (GCS). This scale groups injuries as mild, moderate or severe based on a total score. However, while this has several limitations, these can partly be addressed by combining it with the GCS – Pupils score [4]. For example, the labels “mild” and “severe” can carry a stigma and do not adequately describe the full injury spectrum of TBI severity, which is a continuum [5]. The GCS based system also focuses solely on clinical consciousness level and ignores other important diagnostic indicators such as the brain imaging or blood biomarkers. These limitations can lead to barriers in follow up care.
In response to this problem, the US National Institutes of Health – National Institute of Neurological Disorders and Stroke (NIH-NINDS) convened an international expert initiative in 2022 to rethink how acute TBI is characterised and labelled.
Ninety-four experts from 14 different countries, including the UK, were involved in a structured, consensus-based, process across multiple working groups to systematically evaluate evidence and develop recommendations.
Of the participants, clinicians, researchers, implementation scientists, and individuals with lived experience were all involved. The goal was to create a more precise and multidimensional framework for acute TBI that could be used to improve clinical care and research validity.
The core output of the initiative is a new characterisation system called CBI-M, which integrates four key pillars of assessment.
The clinical pillar uses the GCS scores and pupillary reactivity (which is how the pupil in our eyes reacts to light), offering richer clinical information than GCS alone. The GCS measures eye opening, verbal and motor response. Scores on these areas are summed, and result in a total which ranges from 3 to 15. Traditionally, scores between 3 and 8 have been described as severe, those between 9-12 as moderate, and those between 13–15 as mild [4, 5]. In addition to this scale, the use of automated pupil responses has been recommended. There are three possible outcomes: both pupils respond to light, only one pupil responds, neither pupil responds [4]. The assessment of signs and symptoms has also been noted as an additional component, including symptoms such as headache, dizziness and sensitivity to noise. Incorporating pupillary reactivity builds on prior evidence that combining GCS with pupil assessment improves prognostic accuracy [4].
The biomarker pillar incorporates blood-based biomarkers that reflect biological mechanisms of injury (e.g., markers of neuronal damage or inflammation) [8]. Biomarkers within the blood can indicate that microstructural damage occurred in patients with normal CT (computerised tomography) scans [8]. Initially biomarkers were only used in research, however, they have become increasingly used in clinical settings to provide objective indicators of tissue damage prior to CT scans [9, 10].
The imaging pillar uses imaging measures such as CT or MRI (magnetic resonance imaging) to identify and describe the extent and pattern of structural damage to the brain. This pillar focuses on the CT scan, the most used imaging technique within the first 24hrs after injury [8].
The modifier pillar accounts for other factors that influence presentation or outcomes, such as age, pre-existing health conditions, medication, or other traumatic injuries. Presentation, recovery and outcome of TBI are all influenced not only by the biomechanical and physiological features of the brain injury event but also by social, psychological and environmental factors specific to each individual [11]. The relevance of these modifiers varies by sub-population (e.g., gender) [12]. Some of the modifiers have early effects (e.g. hypotension), whereas others can influence the course of recovery (e.g., mental health, substance misuse) [13]. Modifiers are not measures of injury severity, but contextual factors that influence clinical course and outcome.
Together, these four pillars aim to provide a multidimensional, individualised profile of TBI rather than the simplistic mild-moderate-severe labels.
The CBI-M system, which was designed by involving those with lived experience and fostering a multidimensional and collaborative approach with input from international experts across a wide range of disciplines, aims to reflect the biological and clinical complexity of acute TBI and support personalised clinical management decision-making. This should enhance the scientific validity of future research, including patient clinical trials.
One practical benefit of the new system is the ability to characterise a brain injury with some components of a pillar, when an entire pillar is not available, allowing flexible use. Another benefit is the ability of the system to contribute to the aim of reducing the stigma associated with the traditional labels for injury severity, by providing a more accurate description and prognosis.
A key limitation of the system is the lack of validation in large clinical populations. The proposed framework has not yet been empirically validated in large and diverse patient cohorts, and it has been noted that validation studies are a key priority for future research [3]. Another limitation is the limited evidence available supporting biomarkers and imaging integration. While the framework includes blood biomarkers and advanced imaging, many of these measures are not yet available as a standard, or routinely used in clinical settings.
The system focuses very strongly on the acute phase of TBI, shortly after injury, but does not address the chronic and later stages. It has been reported that 42% of people with a TBI did not seek medical assistance at the time of injury [14], which means that this system would not be applicable to inform their care.
Finally, the implementation of a multidimensional framework could be challenging in environments with limited resources, such as staff and the necessary technology [3]. This raises concerns about the equitable availability across different healthcare systems and makes it more difficult to adopt in fast-paced clinical environments.
The proposers of the CBI-M framework have emphasised that it is not yet a finished clinical tool and that several key steps are needed before this is the case. Validation in large and diverse clinical populations is required, along with an exploration of how it might be applied beyond the acute phase of TBI [3].
The feasibility of this system in different healthcare settings also needs to be assessed, and strategies to assist with this transition are still to be developed [6].
In summary, this initiative moves TBI classification away from a one-dimensional score towards a more holistic characterisation, based on clinical signs, biomarkers and imaging. The intended impact of the proposed CBI-M framework is to improve both patient care and research quality by better capturing the complexity of acute TBI.
