Background on MTBI definitions

When one attempts to define a clinical condition, the definition needs to include operational criteria such that one can clearly demonstrate how one does or does not meet the definitional standard. In the area of mild traumatic brain injury (MTBI; also known as concussion), there have been many attempts to do this. The most widely recognized and cited definitions have been those put forth by the American Congress of Rehabilitation Medicine (ACRM; Kay et al., 1993), the Center for Disease Control and Prevention (2003), the World Health Organization (Holm et al., 2005), the Defense and Veterans Brain Injury Center (2006), and the American Academy of Neurology (1997).

Although all of the definitions put forth by these organizations differ in some respects, they all share one common important feature – they either require the presence of an alteration of mental status or require the presence of an alternation of mental status if more strong indicators of brain injury are not observed (e.g., seizures per the CDC definition). An example is that the ACRM criteria states that the alteration of mental status criteria can be substituted by the presence of a focal neurological deficit (e.g., loss of vision not due to an eye injury). This is because a focal neurological symptom would be strongly indicative of brain injury. Likewise, an alteration of mental status can reasonably attributed to brain injury provided other causes have been ruled out such as a panicked state at the time of injury or alcohol intoxication. Unlike focal neurological symptoms, vague symptoms such as dizziness or headaches can be caused by many different factors and therefore should not be readily attributed to brain damage. Since it is not as easy to detect mental status change in infants (compared to adults) if there is not a loss of consciousness, the CDC allows for lethargy, irritability, and vomiting to count towards the definition of concussion with infants. However, irritability and vomiting are not counted towards the definition of concussion in adults.

From a historical perspective it should be noted that the classic work of Ommaya and Gennarelli (1974) included the requirement of mental status change when they defined a cerebral concussion as “...a grade set of clinical syndromes following head injury wherein increasing severity of disturbance in level and content of consciousness (emphasis mine) is caused by mechanically induced strains affecting the brain in a centripedal sequence of disruptive effect on brain function and structure.”

In 2001, the Concussion in Sports Group (CISG; Aubry et al., 2002) met in Vienna and put forth a “definition” of concussion that reads as follows: “Concussion is defined as a complex pathophysiological process affecting the brain, induced by traumatic biomechanical forces.” The CISG then goes on to describe some features of concussions, such as that they are typically associated with normal brain scans. The main way that the CISG definition differs from those of other organizations is that it is non-operational. That is, CISG only provides an abstract definition (i.e., complex pathophysiological process) with some descriptive features, but provides no clearly operationally defined way to show how a concussion definitively manifests. The CISG does describe some symptoms that indicate that a concussion should be suspected (emphasis by Aubry et al., 2002) such as headaches and dizziness or which may indicate (emphasis mine) that a concussion has taken place. However, these are all statements of possibility and therefore the presence of such symptoms does not define a concussion per the CISG guidelines.

What follows below is a compilation of operational definitions of mild traumatic brain injury, listed in alphabetical order.

American Academy of Neurology

“Concussion is a trauma-induced alteration in mental status (emphasis mone) that may or may not involve loss of consciousness. Confusion and amnesia are the hallmarks of concussion. The confusional episode and amnesia may occur immediately after the blow to the head or several minutes later. Close observation and assessment of the athlete over some period of time is necessary to determine whether evolving neuropathologic change associated with concussion will lead to a confusional state or to the development of memory dysfunction. A history of re-cent head trauma outside the sports setting, such as a motor vehicle accident, should be considered in the evaluation of an athlete with concussion. Frequently observed features of concussion are listed in table 1.

Table 1: Features of concussion frequently observed

Vacant stare (befuddled facial expression)

Delayed verbal and motor responses (slow to answer questions or follow instructions)

Confusion and inability to focus attention (easily distracted and unable to follow through with normal activities)

Disorientation (walking in the wrong direction, unaware of time, date. and place)

Slurred or incoherent speech (making disjointed or incomprehensible statements)

Gross observable incoordination (stumbling, inability to walk tandem/straight line)

Emotions out of proportion to circumstances (distraught, crying for no apparent reason)

Memory deficits (exhibited by the athlete repeatedly asking the same question that has already been answered, or inability to memorize and recall 3 of 3 words or 3 of 3 objects in 5 minutes)

Any period of loss of consciousness (paralytic coma, unresponsiveness to arousal)”

AAN also established a grading symptom for concussions, referred to as grade 1, 2, and 3. Although some clinicians have been known to label concussions as mild, moderate, or severe, it is important to note that this terminology was not used in AAN’s official grading system. The criteria for grade 1, 2, and 3 concussions are as follows:

GRADE 1

1. Transient confusion

2. No loss of consciousness

3. Concussion symptoms or mental status abnormalities on examination resolve less than 15 minutes.

Grade 1 concussion is the most common yet the most difficult form to recognize. The athlete is not rendered unconscious and suffers only momentary confusion (e.g., inattention, poor concentration, inability to process information or sequence tasks) or mental status alterations. Players commonly refer to this state as having been "dinged" or having their "bell rung."

GRADE 2

1. Transient confusion

2. No loss of consciousness

3. Concussion symptoms or mental status abnormalities on examination last more than 15 minutes

With Grade 2 concussion, the athlete is not rendered unconscious but experiences symptoms or exhibits signs of concussion or mental status abnormalities on examination that last longer than 15 minutes (e.g., poor concentration or post-traumatic amnesia). Any persistent Grade 2 symptoms (greater than 1 hour) warrant medical observation.

GRADE 3

1. Any loss of consciousness, either brief (seconds) or prolonged (minutes)

Grade 3 concussion is usually easy to recognize—the athlete is unconscious for any period of time.

American Congress of Rehabilitation Medicine

“A patient with mild traumatic brain injury is a person who has had a traumatically induced physiological disruption of brain functioning, as manifested by at least one of the following:

1. any period of loss of consciousness;

2. any loss of memory for events immediately before or after the accident (amnesia);

3. any alteration in mental state at the time of the accident (eg, feeling dazed, disoriented, or confused); and

4. focal neurological deficit(s) that may or may not be transient.

but where the severity of the injury does not exceed the following: