Post-Traumatic Amnesia – Disorder of the Save Button
Post-Traumatic Amnesia – Failure to Save Memory
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Post-Traumatic amnesia. Does it exist if it wasn’t documented? Injured quarterbacks have press conferences. Survivors of motor vehicle accidents are asked what day it is. As I type this, I could not tell you without looking at my watch what day it is. But I can tell you words I typed hours ago.
Any number of quarterbacks have returned to play in the game in which they suffered a concussion yet had amnesia for the events of the game they completed. Knowing what day it is tells the diagnostician almost nothing about amnesia. A press conference with a bevy of reporters asking questions about very specific plays and decisions will tell us a lot more. When the quarterback cannot remember the game where he lead his team to victory, that is irrefutable evidence of brain injury.
There are three primary problems with our triage for post-traumatic amnesia and the quarterback analogy illuminates all three:
- Post-traumatic amnesia can occur without confusion or other symptomatology;
- Post-traumatic amnesia, can begin minutes or hours after an accident, interrupted by brief episodes of clear memory; and
- Post-traumatic amnesia cannot be fully evaluated unless the injured person is evaluated in the days after the accident, until the amnesia resolves.
But before we spend multiple pages talking about post-traumatic amnesia, we need to discuss why it is important.
For most of modern medical science, all but the best of doctors applied one simple rule to the diagnosis of brain injury: if the individual was not knocked out, then no brain injury occurred. The term “loss of consciousness” is used in lieu of “knocked out” and it is typically abbreviated, as we will do “LOC.” Without an acute (meaning while the person was still symptomatic of the concussion) diagnosis, there could be no later diagnosis of brain damage.
While there were exceptions to this rule, until the last generation, almost all medical doctors applied the rigid LOC rule to virtually everyone who did not subsequently lapse into a coma or need brain surgery. The principal exceptions:
Delayed Loss of Consciousness. Immediate LOC was never required for there to be brain damage diagnosis in cases of increasing intracranial pressure (“ICP”). See our treatment of severe brain injury.
Penetrating Head Injury. Cases where there was penetration of the skull without a LOC. For example, nail guns can penetrate the brain without there being a loss of consciousness. There is the famous case of Phineas Gage, where a large iron rod penetrated his head without knocking him out.. There even are cases of bullets penetrating the brain without a LOC.
Finally, about 1990 some significant recognition spread throughout the medical world that LOC was not a requisite element of a brain injury. The most significant step in this direction was the definition of Mild Traumatic Brain Injury (“MTBI”) by the American Congress of Rehabilitation Medicine (“ACRM”). That definition gave three additional alternative acute events that could point to the existence of the MTBI. The four acute events of concussion were as follows:
- Change in Mental State
- Amnesia or
- Focal Neurological Deficits.
Of the above four elements, the most significant for predicting outcome is post-traumatic amnesia. (The existence of retrograde amnesia, would also be significant, but as significant as post-traumatic amnesia because of its relative rarity in a concussion.) Post-traumatic amnesia is also the only element with any realistic hope for being documented in a person who has a short term change in mental function around the time of the trauma. This statement is well documented by objective, albeit somewhat limited research and also by any examination of cases studies of amnesia, of which there are legions. The problem with the objective studies of amnesia is the objective portions of the tests do not ask questions that properly distinguish between amnesia and confusion which we will discuss in detail below.
According to Lezak, Neuropsychological Assessment, 4th, page 160, citing Bigler 1990, the length of post-traumatic amnesia classifies the severity of a brain injury as follows:
- Less that five minutes, very mild.
- 5 minutes to 60 minutes, mild.
- 1 to 24 hours, moderate.
- 7 days, severe.
- 1-4 weeks, very severe
- More than 4 weeks, extremely severe.
But the key to applying Bigler’s scale is first understanding what post-traumatic amnesia is and then assuring that the diagnostician asks and records the right questions.
Amnesia, and particularly post-traumatic 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 post-traumatic 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 question out of 10 that does more that test for confusion. 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 take into account 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.
 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, cut and paste this web link: http://www.tbilaw.com/AboutMildBrainMovie.php
 The most universal test for classifying brain injury is the Glasgow Coma Scale, but it has little value in a mild brain injury case. 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.