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Wednesday, December 14, 2011

All Brain Injuries are Not the Same: Part 1

One of the most popular myths in the media and among some health care providers is that traumatic brain injury (TB) can be discussed as a unitary concept. In other words, the topic is discussed as if it is not necessary to make a distinction between a mild and moderate to severe TBI. In fact, it is quite necessary to make the distinction rather than broadly discussing the effects of “brain injury.”

Unfortunately, what often happens is that findings from patients with moderate to severe TBIs are misapplied to those with injuries on the mild end of the spectrum. As Dr. Michael McCrea (2008) writes in his evidence based text, moderate to severe TBI is a completely different animal than mild TBI (also known as concussion). There are many examples, which are nicely summarized in McCrae’s text and the interested reader should read that book for specific references supporting the statements below. Some of these examples are presented and expanded upon below to help better inform the public.

1. USEFULNESS OF SEVERITY GRADING TOOLS: In moderate to severe TBI, there are measures available that are useful for grading the severity of the injury whereas the scales on the mild end of the spectrum are not as helpful. The most commonly used severity index is the score on the Glasgow Coma Scale (Teasdale & Jennett, 1974) which assesses level of consciousness. The scale ranges from 3 to 15 points and provides a way to rate patients on their eye movements, motor responses, and verbal responses. The TBI classification scheme based on the GCS is as follows: 13-15 (mild), 9-12 (moderate), and 3-8 (severe). While a significant injury and/or alteration in consciousness is required to obtain a GCS score between 3 and 12, the same cannot be said for the mild end of the TBI severity range. For example, consider a person who merely bumps his head into a wall with a minimal degree of force that was not significant enough to cause a brain injury. Assume, however, that the person develops a headache and is concerned that he has a brain injury, causing him/her to go to the ER. When the person goes to the ER, he/she is physically examined and a GCS score of 15 is assigned because there were no abnormalities with eye movements, motor responses, or verbal responses. According to the criteria above, a GCS score of 15 is equated with a mild TBI. Clearly, however, this example shows a GCS score of 15 does not always equate to brain injury.

2. ACUTE INJURY CHARACTERISTICS: In moderate to severe TBIs, the acute injury characteristics are the strongest predictors of outcome. In mild TBIs, there is only a limited correlation between acute injury characteristics and outcome. For example, in mild TBI, a brief and transient loss of consciousness is not strongly predictive of outcome. Conversely, loss of consciousness in a severe TBI patient, which could last for weeks and beyond, is strongly correlated with outcome. One of the problems is that acute injury characteristics are not as clearly documented in MTBI cases because of a lack of witnesses and the transient nature of the event. For example, a mild TBI patient may lose consciousness for a few minutes but if no one was present to witness this, it cannot be confirmed. Conversely, in a moderate to severe TBI case, LOC usually lasts long enough such that paramedics or some other observer would be able to confirm its presence.

3. CRITERIA FOR DIAGNOSIS: The criteria for diagnosing moderate to severe TBI tends to be more consistent throughout the literature compared to mild TBI. The criteria used to diagnose MTBI are largely based on self-reported subjective symptoms (e.g., altered mental status) without collaborating and/or objective data (e.g., witnesses, neuroimaging findings). In moderate to severe TBI, objective data are often sufficient enough (e.g., diffuse bleeds throughout the brain) such that self-report is not required to make the diagnosis.

Come back tomorrow for part 2, in which more distinctions will be provided.

 REFERENCES


McCrea, M. (2008). Mild traumatic brain injury and postconcussion syndrome. The new evidence base for diagnosis and treatment. New York: Oxford University Press.


Teasdale, G, Jennett, B. (1974). Assessment of coma and impaired consciousness. A practical scale. Lancet, 2:81–84.

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