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Defining the Future of Concussion

Take a moment to think about the future of understanding concussion.

Despite significant financial investment in concussion research during the past decade, there is no evidence-based research that explains the natural history of concussion. We know many things, but most of our concussion knowledge is based on consensus statements. Let’s consider, for example, the definition of concussion – there are more than 42 working definitions of concussion. In an attempt to determine the evidence basis for these definitions, researchers from the Brain Trauma Foundation performed an analysis of the literature with regard to concussion definition. Of 5,437 abstracts, 1,333 were available for full-text review. Of those, 182 articles met inclusion criteria with regard to reasonable evidence basis, and of these articles, only 26 had a sound evidence basis for a concussion definition. The overwhelming majority of articles that define concussion utilized literature that was based on consensus opinion and most of the consensus articles were recirculated.

Why is this an issue? Let’s explore the Zurich 12 definition of concussion*:

Concussion is a brain injury and is defined as a pathophysiological process affecting the brain, induced by biomechanical forces. Several common features that incorporate clinical, pathologic and biomechanical injury constructs that may be utilized in defining the nature of a concussive head injury include:

  1. Concussion 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. Concussion 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 over a number of minutes to hours.
  3. Concussion may result in neuropathological changes, but the acute clinical symptoms largely reflect a functional disturbance rather than a structural injury and, as such, no abnormality is seen on standard structural neuroimaging studies.
  4. Concussion results in a graded set of clinical symptoms that may or may not involve loss of consciousness. Resolution of the clinical and cognitive symptoms typically follows a sequential course. However, it is important to note that in some cases symptoms may be prolonged.

 

Although this definition appears to be comprehensive, we are left with the following shortcomings:

  1. This definition presents concussion as a homogenous entity. There is no reference to the area(s) of the brain that is dysfunctional, and the level of dysfunction is not specified. An individual with right dorsolateral pre-frontal lobe dysfunction will manifest in a much different manner than someone with midbrain dysfunction.
  2. The ‘pathophysiological process’ is not specified further. Although this all-encompassing description might at first glance seem to cover the bases, there is no specificity with regard to the actual underlying pathophysiology. Axonal stretch will manifest differently than axonal shearing. Brain micro-hemorrhage will present differently than no hemorrhage. A microglia-induced inflammatory process will manifest differently than a process without inflammation.
  3. The notion of ‘short-lived impairment’ creates an environment in which concussion could be treated as other well-known clinical entities with short-lived neurological impairment such as burners and stingers. The impairment often lasts days, and may be more prolonged, and we don’t understand the basis for such impairment.
  4. When we describe concussion as a ‘functional disturbance,’ we create an environment in which concussion is treated simply as a metabolic derangement without physical consequence. Concussion may involve acute micro-hemorrhages along the axons that can be detected with standard 3Tesla MRI machines. This is much different than a functional metabolic change.
  5. When our focus on concussion is a set of graded clinical symptoms, we are focused solely on subjective criteria.

 

Please join us in keeping an open mind with regard to concussion diagnosis and management. We can simultaneously work with current guidelines (derived from the best available research) while taking an evidence-based look at where we need to go so that we can diagnose and manage this condition with more specificity.

 

*McCrory P et al. Consensus statement on concussion in sport: the 4th International Conference on Concussion in Sport held in Zurich, November 2012. Br J Sports Med 2013; 47:250-258.