Tuesday, December 18, 2007

Traumatic Brain Injuries

The Lancet 2007; 370:1879
Grappling with traumatic brain injury
Vastly improved trauma care on the battlefield is one of the great success stories of modern medicine. One of its grimmer outcomes, though, is the spectre of badly wounded soldiers who survive their injuries, but with multiple, often severe disabilities. Survival rates have greatly increased, but an acceptable quality of life might be an entirely different matter. Traumatic brain injury and its sequelae are increasingly common in soldiers returning from Afghanistan and Iraq, which poses serious challenges for medicine and society.
USA Today recently calculated that some 20000 US troops might have signs of traumatic brain injury, a number five times greater than the Pentagon's official tally. (Veterans with injuries discovered after leaving war zones are not included in official statistics.) In previous US wars, the military estimated the frequency of traumatic brain injury at 14-20%. But now, with more than half of all combat injuries resulting from explosive devices, that proportion has increased to nearly 60%, according to 2004 US military data. Blasts from rocket-propelled grenades, landmines, and improvised explosive devices have sharply increased the number of soldiers with traumatic brain injury. One of the confounding factors in making an accurate determination of the frequency of brain injury is that, as the Department of Defense acknowledges, the US military has neither a uniform definition of traumatic brain injury nor a method of systematically reporting it.
The military's problems in part reflect the state of the science of head injury. Much about traumatic brain injury is not well understood, especially blast-related injury. Whether the mechanisms of blast-related brain injury are the same as those known from more conventional head injuries is unclear. Changes in atmospheric pressure caused by the explosion are at least partly the mechanism of primary blast injury. But because explosions also release acoustical, thermal, electromagnetic, and other types of energy, it is no longer certain that overpressure alone causes primary traumatic brain injury; the physics of the event require further investigation. And some components of explosive devices, such as trinitrotoluene, are toxic, perhaps neurotoxic, but the effects of other elements need to be understood as well.
Unfortunately, no good experimental models of blast-induced brain injury exist. Although rodents provide a great deal of reliable information about memory, it is hard to ask a rat about emotional lability and trouble concentrating. Clinically, post-concussive injury is difficult to distinguish from post-traumatic stress disorder, which is also common in this population. The two disorders have some characteristics in common, and the difference between the symptoms of mild traumatic brain injury-problems with memory, attention, and concentration, and headaches, sleep disturbances, irritability, and depression-and those of post-traumatic stress disorder can be subtle.
Screening for signs of head injury, now done routinely in all returning veterans, poses its own challenges. The results naturally depend on what the screening consists of-eg, whether questionnaires are used or formal neurological examination is done. Furthermore, signs and symptoms might appear well after the actual traumatic event. Many diagnoses of traumatic brain injury depend on self-reporting or complaints from family members and friends. More standardised, less emotionally fraught, and cost-effective measures are needed. Biomarkers, an area of intense investigation, would make for a definitive diagnosis, but these remain to be elucidated.
With its mechanisms murky, diagnosis tricky, incidence under-reported, treatment uncertain, and personal, societal, and economic tolls enormous, traumatic brain injury is a clear crisis for the US military. The Department of Defense is pouring millions of dollars into research on the injury, and has just established a Defense Center of Excellence for Psychological Health and Traumatic Brain Injury. But does traumatic brain injury deserve attention outside a military setting? Absolutely. Brain-injured veterans join an estimated 1·4 million cases of traumatic brain injury among civilians that occur each year in the USA alone. In a civilian population, the main causes are falls, road accidents, hitting or being hit by an object, and assaults. In the USA alone, about 5·3 million people are disabled as a result of traumatic brain injury. These statistics are not trivial.
In view of the costs of the wars in Afghanistan and Iraq, putting resources into research on the health consequences for military personnel is not only the pragmatic thing to do, but also, according to all available scientific and medical evidence, urgently needed. The results of such research will benefit soldiers and civilians alike.
The Lancet

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