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Evolution in the Understanding of Concussion – Length of Amnesia Correlates to Severity of Brain Damage

Continuing on with the discussion of my Concussion Clinic videos, today’s topic is The Length of Amnesia is the Best Predictor of Severity of Injury. Today’s video is here:

Brain injury is one of those things that everyone feels the need to classify, typically into categories of mild, moderate and severe. A severe brain injury is one that involves extended coma. I don’t have any trouble with that definition for severe brain injury.

The controversy in classifying brain injuries revolves primarily around whether there was a brain injury at all and where the break point is between mild and moderate brain injury. The problem with all classification battles in the mild to moderate category is too much is based upon the identification of symptoms in the first hour, where it is not how symptomatic a person is at two hours, but how long the symptoms last that is significant. This is especially true with the most predictive symptom, amnesia.

With respect to severe brain injury, the Glasgow Coma Scale is a reasonably accurate indicator of severity. It also has the benefit of nearly universal adoption, making outcome studies based upon it reliable because of the large number of patients studied. But when the brain injury is below the severity level that loss of consciousness or a change in mental state is witnessed by a medical professional, the GCS has little validity. Most concussed individuals will get the highest score of 15, regardless of how significant the concussion is and how symptomatic they are at the time given the score. The GCS score at the mild end is only a test for confusion, not amnesia. To get a “perfect” GCS score, a patient needs only have his eyes open, be able to carry on a conversation demonstrating orientation (he knows who he is and where he is) and that he can follow simple commands. Compare that to how oriented a quarterback must be to continue to play in the game.

In contrast, basing outcome on the length of amnesia not only correlates well with the GCS score in the severely brain injured population, it is sensitive enough to provide meaningful diagnostic guidance in the less severely injured. According to Lezak, Neuropsychological Assessment, citing Bigler 1990, the length of amnesia predicts as follows:

  • Less that five minutes, very mild.
  • 5 minutes to 60 minutes, mild.
  • 1 to 24 hours, moderate.
  • 1- 7 days, severe.
  • 1-4 weeks, very severe.
  • More than 4 weeks, extremely severe.


But the key to applying this score is first understanding what amnesia is and then assuring that the diagnostician, asks and records the right questions. Amnesia is not like the Hollywood head injury myth, where the main character does not remember who he is until he magically flashes on something, or gets that second blow to the head. According to Lezak as amnesia “does not end when the patient begins to register experience again, but only when registrations is continuous.” Lezak, 4th Edition, page 160.

The problem is that distinguishing between some imprinting of memory and “continuous” imprinting of memory does not lend itself to established tests which primarily focus on confusion. One standardized test for amnesia, the GOAT, (“Galveston Orientation and Amnesia Test”) has only one good question out of 10. The best question on the GOAT is “can you describe in detail the first event you remember after the accident.” But because this is the “subjective” question, it is the one researchers pay the least attention to. But even this best question, doesn’t account for the fact that amnesia may begin after the period for which this question is being asked. It is not what the person remembers about the first 10 minutes post-accident, it is what they continuously remember the next hours and days that is significant.

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