Controversies in Concussion Frequently Encountered by Attorneys and Expert Forensic Neuropsychologists: Subconcussion or Subconcussive Blows
Some of the most significant controversies in the field currently relate to (1) diagnosis of TBI retrospectively (particularly concussion), and (2) chronic symptoms following TBI. It is difficult, in some cases, for experts to agree on short and long term consequences of mild TBI. Particularly controversial as well is the condition known as chronic traumatic encephalopathy (CTE) which is thought by some to be due to repeated concussive (or sub-concussive) blows. Cases of claimed or reported TBI become particularly challenging when the potential injury is unwitnessed or unreported at the time the injury was reportedly experienced. This can be seen in military populations, where reporting of injury was downplayed or hidden to avoid duty limitations or to “remain in the fight.” Other individuals may also downplay symptoms to avoid job loss or negative evaluations. This can be particularly easy to do in cases of reported “subconcussive blows,” although the idea that such “blows” would have lasting impact has had insufficient research support.
It is important to remember amid all of the controversy that severity of TBI is determined at the time of injury and not by level of functioning at some later point in time. The DoD and VA healthcare systems use the American Congress of Rehabilitation Medicine (ARM) 1993 criteria are commonly accepted, but other classification systems are used as well.
Currently, some people are arguing for broader inclusion of suspected concussion and that the threshold for diagnosing concussion should be lowered. At this point, the research on lowering the concussion threshold (for example, on subconcussive blows) is largely theoretical and has not been supported sufficiently in the scientific literature to gain more wide acceptance. Some initial studies suggest that there could be white matter changes in some subset of individuals with subconcussive blows, but it is not know what is meant by that.
As far as I can tell, some researchers are suggesting that a subconcussive blow does not reach the threshold of a concussion or mild TBI but yet is thought to have some sort of lasting impact on a person’s functioning or lead to lasting symptoms. This research raises more questions than answers. For example, how would a subconcussive blow differ from bumping or striking one’s head? What is the threshold of force required to be considered a subconcussive blow? How many subconcussive blows would one have to experience to equate to the impact of a more significant injury? Is there any consistent relationship between subconcussive blows and cognitive functioning? I have not observed a trend in the literature to suggest that there would be a relationship between subconcussive blows and cognitive functioning, as of this writing. In general, the notion of subconcussive blows implies a fragility of the brain that may not be substantiated by the overwhelming body of literature. The brain as we know it is not an “eggshell.” Instead, it is cushioned by a natural shock absorption system, the cerebrospinal fluid. The brain is also designed to endure a temporary disruption in functioning, many argue, as cognitive and emotional symptoms of mild TBI virtually always resolve within a few days to weeks of concussion.
The worry and beliefs about negative outcomes associated with subconcussive blows may have outpaced the research for the time being. Decades of research ahead will have the last word!