Goldstein LE, Fisher AM, Tagge CA, Zhang XL, Velisek L, Sullivan JA, Upreti C, Kracht JM, Ericsson M, Wojnarowicz MW, Goletiani CJ, Maglakelidze GM, Casey N, Moncaster JA, Minaeva O, Moir RD, Nowinski CJ, Stern RA, Cantu RC, Geiling J, Blusztajn JK, Wolozin BL, Ikezu T, Stein TD, Budson AE, Kowall NW, Chargin D, Sharon A, Saman S, Hall GF, Moss WC, Cleveland RO, Tanzi RE, Stanton PK, McKee AC.
Chronic traumatic encephalopathy in blast-exposed military veterans and a blast neurotrauma mouse model.
Sci Transl Med. 2012 May 16;4(134):134ra60.
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This is a very interesting paper demonstrating that the neuropathology seen in some soldiers exposed to blast overpressure with clinical symptoms suggesting chronic traumatic brain injury is very similar to that of athletes with repetitive concussive head injuries. Importantly, a carefully calibrated mouse model was developed in which it was shown that blast overpressure per se does not injure the brain; instead, it is the head movement induced by the blast that causes the brain trauma. This is well known to any boxer: Make the head on your opponent accelerate in an uncontrolled manner and you will have a good chance of winning the bout on a knockout. The mouse model will be very useful for finding strategies to prevent a progressive tauopathy from developing after brain trauma.
The study is very interesting, and there are a few groups that are obtaining similar results with their animal models.
There has been a big controversy about the relevance of head impact studies to military trauma. There is a large group that assumes that the physics of blast waves is completely unrelated to head impacts of the type received during car accidents, playing football, falling on the ice, and the like. This study provides a good argument that they are, in fact, similar injury mechanisms. Effectively, the blast wave passes through the skull and brain, but it isn't until the blast wind causes a shock to the head that you get the damaging relative motion between the brain and the skull. It does not take a lot of displacement to cause an injury; a rapid acceleration is sufficient.
There are some possible issues to consider. The skull of a mouse will not impede the blast wave very much, but we know that pig skulls alter the blast wave considerably. Human skulls are going to be somewhere in between, and we don't necessarily know what effect that might have. It is also likely that a large enough blast wave will just liquefy most of the internal organs. Having said that, I think these results provide pretty convincing evidence that the physics of head trauma are dominated by the impulse delivered to the head.
Lastly, I think the fact that there seem to be similar mechanisms involved in military and sports head traumas provides circumstantial evidence that PTSD and CTE are related, but there is the potential for a number of other factors to be involved in PTSD. One of the most important things we can do to help soldiers and athletes is to find ways to detect the damage early and localize it to specific structures in the brain. This would enable clinicians to develop treatments specific to a given patient. Because of this study, I think we are much closer to reaching that goal.