Troops who do not pass the smell test are likely to have traumatic brain injury

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Decreased ability to identify specific odours can predict abnormal neuroimaging results in blast-injured troops, according to a new study by US federal researchers released online in the journal Neurology.

The US Department of Defense-funded study, led by Michael Xydakis, associate professor of Surgery in the F Edward Hebert School of Medicine at the Uniformed Services University of the Health Sciences (USU), and his colleagues from USU, Walter Reed National Military Medical Center, and the National Institutes of Health, found that testing the sense of smell can be used to assess memory impairment following trauma.

The team, which included Lisa P Mulligan, Walter Reed National Military Medical Center Department of Neurosurgery; Alice B Smith, Cara H Olsen, and Dina M Lyon, from the Uniformed Services University of the Health Sciences, and Leonardo Belluscio, National Institute of Neurological Disorders and Stroke, NIH, studied more than 231 acutely injured polytrauma inpatients at Walter Reed National Military Medical Center who had been air-evacuated from combat zones in Afghanistan or Iraq. Each soldier was evaluated for traumatic brain injury and then administered a test of their sense of smell using the University of Pennsylvania Smell Identification Test.

The olfactory system processes thousands of different odours, sending signals to the brain which interprets the smell by linking it to a past memory. If memory is impaired, as is the case with Alzheimer’s disease, sleep deprivation, and acute traumatic brain injury, the task is not entirely possible. When the smell test was abnormal in a subject, those soldiers were all found to have abnormalities on their brain scans. 

“Although it may seem far-fetched that the sense of smell can be used to identify a concealed brain injury, olfactory impairment was commonly used by neurosurgeons in attempts to localize certain brain tumours prior to the use of advanced neuroimaging in the 1980s,” said Xydakis.

The investigators then concluded that this kind of methodology could be used in combat theatres to assist deployed physicians in determining which injured troops would require immediate neuroimaging, thus significantly enhancing frontline neurologic combat casualty care.

“Getting a CT scan in a combat zone is often the equivalent distance of placing a soldier on a helicopter in Washington, DC, and sending them to Boston. It requires a significant investment in personnel and aviation resources; not to mention flying troops over hostile terrain. Using abnormalities with the sensory systems has opened up an entirely new avenue of investigation for diagnosing brain injuries,” Xydakis said.

The study was funded by the Department of Defense Combat Casualty Care Medical Research and Development Program.

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