Every war has a signature injury associated with it. For World War 1, it was said to be “shell” shock. Post-concussional syndrome gained importance in World War 2. “Agent Orange” came into discussions during and after the Vietnam War.

“Traumatic Brain Injury,” or TBI, is reported to be one of the signature injuries in the Iraq and Afghanistan wars.  In a recent 2015 study, the participants were selected from the US service members who were acutely injured in combat operations in Iraq and Afghanistan and immediately transported back to the US from the combat zones.  All participants had sustained severe blast injuries and were assessed to have “closed neurologic head trauma.”

In this cohort study, the soldiers were initially evaluated for traumatic brain injury and subsequently administered the “smell test.” When the sense of smell is impaired in an individual, there are two mechanisms of dysfunction that can be tested; either a direct effect on the intranasal olfactory receptors or a problem with the neuronal network in the central nervous system (CNS). The blast injured soldiers with no or mild TBI had normal senses of smell, whereas those with TBI had atypical smell test results. In all the groups, a direct impairment of the smell receptors in the nose due to inhalation of chemicals, etc. was ruled out, indicating that the damage resided within the CNS.

Follow-up neuroimaging showed injury to the frontal or temporal lobes in the brains of the soldiers who exhibited an impaired sense of smell. The authors state in the article that “damage to these regions, whether from brain trauma, stroke, or through neurodegenerative processes (e.g., premotor Parkinson disease, Alzheimer disease, multiple sclerosis, frontotemporal dementia), has been demonstrated to significantly impair memory and thereby the ability of the brain to correctly match up and link common inhalational odorant molecules to past learning and experience.”

In a combat zone, injured soldiers have to be evacuated and brought to the USA for assessment and treatment. The authors state “The presence of measurable abnormalities with central olfactory dysfunction provides added value to the practicing physician for preclinical detection of intra- cranial injury and, accordingly, subsequent disease- modifying early interventions.”