neuropsychology assessment

Acquired Brain Injury:

Towards Contemporary Classification of Severity for Acquired Brain Injury (ABI)

A neuropsychological assessment is extremely useful in providing details to aid in prognosis and treatment when someone has sustained an injury either through a car accident or otherwise. When considering classification of the severity of an acquired brain injury, it is important to note that severity is in not always predictive of the outcome. More specifically, people with severe brain injuries can have positive outcomes and there are circumstances where people with a lower classification of severity can have a poorer outcome.

There are many factors that influence the severity of an acquired brain injury. This can include factors such as the site and size of the damage to the brain, the developmental stage of the individual and other factors related to the person and the environment. The severity and outcome following a brain injury may indeed be an expression of the total interaction of the factors.

Neuropsychology Assessment and Classification

The measurement and classification of severity, however, is different. The severity of an acquired brain injury is gained from obtaining information about a person’s mental state and level of consciousness following an injury where there is a suspicion that the brain has sustained some form of damage. Tests and procedures have been developed in an attempt to standardise the data obtained about a person’s state and, overtime, classifications have been associated with performances on these measures and procedures. The two main classification tools / processes used today include the Glasgow Coma Scale and measurement of Post Traumatic Amnesia (PTA).This article focuses on the how the duration of PTA is used define severity also proposes an update to the classification system.

Post Traumatic Amnesia (PTA) is also a commonly relied upon state that is used to estimate the severity of an acquired brain injury. Post-traumatic amnesia is considered to be the best single indicator of the severity of closed head injury.PTA is considered to be a state of confusion that is reflective of damage and disruption to the normal operation of the brain. It is characterised by an alteration to attention, orientation and memory (rapid forgetting). A number of measures have been developed to attempt to determine where a person is in a post-traumatic amnesic state. The Westmead PTA scale is scale designed to measure PTA. The Westmead PTA scale uses a series of orientation and memory questions to produce a score out of 12. When a person consistently achieves a score of 12 over a period of time, they are considered to have emerged from PTA. The questions used in this scale are provided below:

How old are you?
What is your date of birth?
What month are we in?
What time of day is it? (Morning, Afternoon or Night)
What day of the week is it?
What year are we in?
What is the name of this place?
Who do you have to remember? (Show set of 3 photos)
What is their name?
What were the 3 pictures that you had to remember?

The duration that a person is considered to remain is PTA is considered as indicative of the severity of PTA. Accordingly, there have been a number of attempts to apportion a period of time to a severity classification. The most traditional measure classification based on PTA duration is detailed in the table below.

PTA Duration Traditional Classification
< 5 minutes Very Mild
5-60 minutes Mild
1-24 hours Moderate
1-7 days Severe
1-4 weeks Very Severe
> 4 weeks Extremely Severe

However, another classification systemplaces into question the consensus and appropriateness of the above classification. This is work that has occurred around classification at the milder end of the severity of brain injury. Specifically, the diagnostic classification criteria for mild traumatic brain injury by the American Congress of Rehabilitation Medicine is detailed below:

Inclusion criteria—one or more must be manifested:

  • • Any period of loss of consciousness forup to 30 min
  • • Any loss of memory for eventsimmediately before and after theaccident for as much as 24 hrs
  • • Any alteration of mental state at the time of accident (dazed, disoriented, orconfused)
  • • Focal neurological deficit(s) that may ormay not be transient Exclusion criteria—one or more must bemanifested
  • • Loss of consciousness exceeding 30 min
  • • Posttraumatic amnesia persisting longer than 24 hrs
  • • After 30 min, the Glasgow Coma Scale falling below 13

As described above, it is clear that the diagnostic criteria for mild TBI by the American Congress of Rehabilitation Medicine excludes persons with a PTA persisting longer than 24 hours. A number of others have also provided further sub classifications of mild TBI and they have typically been characterised by providing sub classification for mild TBI based on the duration of PTA and also extending to 24 hours.

Therefore any person experiencing a PTA less than that of 24 hours is indicative of some form of Mild Brain Injury. This, however, is at odds with the main classification system that includes a moderate classification as a PTA of being between 1 and 24 hours. Indeed, the lack of consensus has led to different research methodologies based on different criteria for mild TBI. Specifically, the duration of post-traumaticamnesia has been 60 minutes or less in some studies and less than 24 hours in others. Such different research methodologies make it difficult for comparison of research findings.

An attempt to amalgamate the traditional classification system along with more contemporary classification approaches for Mild TBI would have the effect of extending the duration for Mild TBI classification. This, inturn, would extend further the duration of PTA required to reach moderate and severe classifications. Very Severe and Extremely Severe Brain Injury classification groups could be condensed into one group, Very Severe. Others have also noted the addition of a further category, that being the chronic amnesia state. This is classification system is detailed here.

PTA Duration Traditional Classification Proposed Classification
< 5 minutes Very Mild Very Mild
5-60 minutes Mild Mild/ Concussion
1-24 hours Moderate Mild / Concussion
1-7 days Severe Moderate
1-4 weeks Very Severe Severe
> 4 weeks Extremely Severe Very Severe
> 6 months   Chronic amnesia state

We appreciate the limitations on any classification system in this areato have difficulties being able to be entirely predictive of outcome. Nevertheless, the proposed new classification system may more likely be reflective of the distribution of outcomes that occur following traumatic brain injury.

In reality, the severity of brain injury can be considered as simply being on a continuum and that PTA duration is an indicator (being correlated with outcome) that is useful towards providing a framework for classification. From a scientific perspective, pure cut off points for classification, while beneficial for making group comparisons, should be used careful in individual cases. There can be no meaningful difference between the person who is in a post-traumatic amnestic state for the duration of 23 hours compared to the person in PTA for 25 hours. Likewise, there are more similarities between person’s in PTA for 6 days or 7 days than there are meaningful differences.

Classification of severity following a traumatic brain injury has serious implications. The terminology can impact directly upon persons with such injuries and how they reflect on their situations, which in turn can have ripple effects on their prognosis. Labels also affect policy decisions and allocation of resources in an appropriate manner. We should strive to have the most accurate and appropriate classification system in order to allow for more tailored responses. Neuropsychology assessment services should consider these factors.

Neurodynamics maintains a high standard of clinical expertise in order to provide accurate assessment information and appropriate interventions. The referral information section provides further details about the areas where a neuropsychological assessment may be useful.


Dr Nathaniel Popp
Clinical Neuropsychologist
BA., MA., DPsych., MAPS., CCN Member
TAC Provider number: 160 603 50
WorkCover Provider number: PS5676B

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