All Concussions Are Different But Share Four Common Features

The 5th International Consensus Statement On Concussion In Sport issued in April 2017 (1)(“Berlin Consensus Statement”) while it modifies slightly the definition of sport-related concussion, continues to note that it provides no insights into the underlying process through which the brain is impaired, fails to distinguish between grades of severity, and leaves unresolved the question of whether concussion is on the same spectrum as  severe traumatic brain injury.

Four common features

The Berlin Consensus Statement continues to define a sport-related concussion (SRC) as a traumatic brain injury induced by biomechanical forces.  While no two concussions are exactly the same, the Berlin Consensus Statement, as with its predecessors, states that they all share four common features which may be utilized in making a clinical diagnosis of concussive head injury:

1. Direct blow to head not required. SRC may be caused either by a direct blow to the head, face, neck, or elsewhere on the body with an impulsive force transmitted to the head.
2. Rapid onset and gradual resolution of symptoms. SRC typically results in the rapid onset of short-lived impairment of neurological function that resolves spontaneously.  However, in some cases, symptoms and signs may evolve of a number of minutes to hours.
3. Brain function disrupted. A concussion may result in neuropathological changes, but the acute clinical signs and symptoms largely reflect a functional disturbance rather than a structural injury to the brain itself, and, as such, no abnormality is seen on standard structural neuroimaging studies.
4. Loss of consciousness not required. Concussion results in a range of clinical signs and symptoms that may or may not involve loss of consciousness.  Resolution of the clinical and cognitive features typically follows a sequential course.  However, it is important to note that in some cases symptoms may be prolonged.

For a diagnosis of concussion, the clinical signs and symptoms cannot be explained by drug, alcohol, or medication use, other injuries, peripheral vestibular dysfunction, etc.) or other co-morbidities (e.g. psychological factors or coexisting medical conditions).

Unresolved issues

While leaving the definition of concussion unchanged, the authors of the Berlin Consensus Statement admit that the operational definition of concussion is not particularly helpful to clinicians in several respects:

First, it provides no “insights into the underlying processes through which the brain is impaired.  Second, it does not distinguish between different grades of severity.  Third, it fails to reflect newer insights into the persistence of symptoms and/or abnormalities on specific investigational modalities,” an issue “clouded not only by a lack of data, but also by confusion in definition and terminology.  The authors specifically note that the use of the term mTBI, which, as noted above, is often used interchangeably with concussion, is “similarly vague and not based on validated criteria.”

“One key unresolved issue,” the Berlin Consensus Statement notes, is whether concussion is part of a TBI spectrum associated with lesser degrees of diffuse structural change than are seen in severe TBI, or whether concussive injury is the result of reversible physiological changes. Because the term concussion, “while useful, is imprecise, and because disparate author groups define the term differently, comparison between studies is problematic.”

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1. McCrory P, Meeuwisse W, Dvorak J, et al. Consensus statement on concussion in sport: the 5th International Conference on Concussion in Sport held in Berlin, October 2016. Br J Sports Med.  2017;51:838-847.

2.  Dematteo CA, Hanna SE, Mahoney WJ. et al. My child doesn’t have a brain injury, he only has a concussion. Pediatrics2010;125(2):327-334.

3.  Giza CC, Hovda DA, The Neurometabolic Cascade of Concussion. J. Ath Train 2001;36(3):228-235.