Most concussion grading systems issued in the 1980's and 1990's, such as the Colorado Medical Society and American Academy of Neurologists guidelines, relied heavily on the loss or non-loss of consciousness (LOC) and the presence or absence of post-traumatic amnesia as indicators of concussion severity. Any LOC, however brief, resulted in the concussion being classified as a Grade 3 (severe) concussion under both these guidelines.

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Under Dr. Cantu's revised guidelines, issued in 2001, less emphasis was placed on LOC as a predictor of injury severity and additional weight given to overall symptom duration. Dr. Cantu classifies a concussion involving LOC of less than a minute as a Grade 2 (moderate) concussion but only if post-traumatic amnesia or other post-concussion signs or symptoms were also present lasting longer than 30 minutes but less than 24 hours, and a concussion involving LOC of more than a minute as a Grade 3 (severe) concussion even if no other post-concussion signs or symptoms are present.

Recent research, however, suggests that LOC and amnesia, either alone or in combination, are not good predictors of injury severity:

• A number of studies have established that brief (less than 1 minute) LOC is not associated with abnormal neuropsychological test results at 48 hours post-injury.

• Studies of high school and college athletes with concussions shows no association between (1) LOC and the duration of symptoms or (2) LOC and neuropsychological and balance tests at 3, 24, 48, 72 and 96 hours post-injury.

• A 2000 study revealed that LOC was present in only 9% of concussions sustained by high school and college football players while other signs and symptoms, such as headache, dizziness, confusion, disorientation, and blurred vision were much more common.

As a result of such studies experts now agree that LOC is not always predictive of recovery after a brain injury. Indeed, the presence of LOC does not even require classification of the concussion as "complex" under the Prague concussion guidelines, the most recently published international consensus statement on concussion in sport.

Loss of consciousness, whether it occurs immediately or after an initially lucid interval, however, may signify a more serious brain injury, so that it should never be ignored, especially if prolonged.

Author: Lindsay Barton
Date created: March 15, 2008
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Related Articles

 Concussion Severity & Return to Play: Prague Consensus Statement
 Concussion Grading Systems And Return-To-Play Guidelines: A Comparison
 Post Traumatic Amnesia

For more on this topic

 What are Concussions?
 Post-Concussion Signs & Symptoms: A Checklist

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