Olfaction is a critical sensory function and changes in the ability to detect smells could affect quality of life by diminishing appreciation of food, drink, and other aroma-based experiences, increase danger of hazardous exposures, and cause a loss of employment. Additionally, decrements in olfaction have been related to onset of some neurodegenerative conditions. Olfactory impairments in military populations are highly prevalent and often attributed to the long-term effects of mild traumatic brain injury (mTBI) and chronic psychiatric disorders. The main goal of this investigation was to examine olfactory function in a cohort of combat veterans using a quantitative smell test.

Participants underwent a neurological examination using a revised version of the Neurological Outcome Scale for Traumatic Brain Injury. Olfactory function was examined using a set of essential oil vials with common odors. Based on the number of correctly identified odors, the following grading system was employed: no deficit; mild; moderate; severe deficit; and absence of smell detection. All study assessments were performed prior to March of 2020 (onset of COVID-19 pandemic). In addition, participants completed performance validity testing (PVT) and screening for ongoing substance misuse using the Alcohol Use Disorders Identification Test and Drug Abuse Screening Test-10. Lifetime history of brain injury, combat-related extracranial injuries, and deployment characteristics were assessed using structured interview. All available medical records were reviewed.

Participants were 38 veterans with a deployment-related mTBI who passed the PVT and did not have ongoing substance misuse issues. Olfactory examination revealed normosmia in 20 participants and various degrees of deficit in 18 (11= mild; 4=moderate; and 3=severe). The groups did not differ in demographics, post-injury interval, or current clinical (non-psychiatric) conditions. Participants with hyposmia frequently reported being exposed to a higher number of blasts and being positioned closer to the nearest primary blast, and more often endorsed a period of loss of consciousness after the most serious mTBI. In addition, they more often reported tympanic membrane perforation, extracranial injuries, and histories of both blast and blunt force mTBI. Comorbid diagnoses of posttraumatic stress disorder (PTSD), depression, chronic headaches, and pain were more common among these participants as well.

Several blast exposure and specific injury-related characteristics increase the likelihood of long-term olfactory impairments, comorbid psychiatric conditions, and chronic pain among veterans with a history of deployment-related mTBI. Notably, none of the participants with hyposmia had a clinical diagnosis of olfactory dysfunction or were receiving service-connected disability for a loss of sense of smell at the time of their assessment. Multidisciplinary rehabilitation care provided to combat veterans with history of mTBI and/or PTSD should include olfactory examination using both quantitative and qualitative smell tests, education regarding the adversities related to loss of smell, management of current psychiatric symptoms, and follow-up assessments. The lack of a comparison group without a history of mTBI and the small sample size were the main limitations of this investigation.