Evolution of the Definition of Concussion

My last blog focuses the acute symptom of amnesia, the symptom that is now believed to be the most significant predictor of outcome after concussion. However, that is the modern way of looking at concussion, and unfortunately, not even all treatises or commentators on brain injury, are even willing to look at amnesia in absence of a documented loss of consciousness at the time of concussion.

I have a fairly extensive library of brain injury treatises in my library, something many of you who have seen my websites or brain injury videos will recognize. If we were going to look at those books, you might be surprised as to how different the definition of concussion is in those books from what is the current thinking about concussion.

For example, one of the treatises that is on more neurologists shelf than almost any other, Adams and Victor, Principles of Neurology- that books says that you can not have a mild brain injury, you can not have a concussion, without a loss of consciousness.

That frankly is wrong.

But this book has been restating that basic principle since it was originally published in 1977. The copy on my shelf was printed in 1997, and the most recent version says the same thing. That is not the current thinking about concussion, not the thinking of the CDC, not the thinking of the American Academy of Neurology. But because it is content on one of the leading treatises in neurologist’s own libraries, it is the thinking of a far greater percentage of neurologists than should in fact be the case.

The definition of concussion really started to change about 1992, even though the research behind that change dates back at least as far as 1971. What happened in 1992 is that there was the American Congress of Rehabilitation Medicine’s (“ACRM”) published its definition of “mild traumatic brain injury.” In that definition, the ACRM abandoned the absolute requirement that you had to have a loss of consciousness to be diagnosed with a brain injury. The ACRM definition substituted this requirement with four different, alternative, what I describe on my website as acute events. Those events were Loss of Consciousness, a Change in Mental State, Amnesia, and Focal Neurological deficits. Source: Mild Traumatic Brain Injury Committee of the Head Injury Interdisciplinary Special Interest Group of the American Congress of Rehabilitation Medicine, published at J Head Trauma Rehabil 1993:8(3):86-87 For the full context of the ACRM definition, click here.

The only one of those that really adds a significant amount to the diagnostic picture is amnesia. But because amnesia is one of those things that doesn’t have a true objective measure and something that is not particularly sensitive to be identified in the emergency room, amnesia has not helped us define mild brain injury/ in the cases where people are long term disabled as much as it should. See the previous blog on Amnesia, and the blogs that will follow later this week.

The 1992 ACRM definition of concussion was ultimately followed by the American Academy of Neurology’s work with concussion in sports. Those two movements had a major impact on changing the definition of concussion. That has ultimately lead to the extremely important “Heads Up Brain Injury in Your Practice “ which is published and distributed by the CDC. For those materials, click here.

Tomorrow: Concussion in Sport and How Relevant that is to Other Concussions