Abstract
Objective: To determine whether a structured and quantitative assessment of differential olfactory performance—recognized between a blast-injured traumatic brain injury (TBI) group and a demographically comparable blast-injured control group—can serve as a reliable antecedent marker for preclinical detection of intracranial neurotrauma.
Methods: We prospectively and consecutively enrolled 231 polytrauma inpatients, acutely injured from explosions during combat operations in either Afghanistan or Iraq and requiring immediate stateside evacuation and sequential admission to our tertiary care medical center over a 2½-year period. This study correlates olfactometric scores with both contemporaneous neuroimaging findings as well as the clinical diagnosis of TBI, tabulates population-specific incidence data, and investigates return of olfactory function.
Results: Olfactometric score predicted abnormal neuroimaging significantly better than chance alone (area under the curve = 0.78, 95% confidence interval [CI] 0.70–0.87). Normosmia was present in all troops with mild TBI (i.e., concussion) and all control subjects. Troops with radiographic evidence of frontal lobe injuries were 3 times more likely to have olfactory impairment than troops with injuries to other brain regions (relative risk 3.0, 95% CI 0.98–9.14). Normalization of scores occurred in all anosmic troops available for follow-up testing.
Conclusion: Quantitative identification olfactometry has limited sensitivity but high specificity as a marker for detecting acute structural neuropathology from trauma. When considering whether to order advanced neuroimaging, a functional disturbance with central olfactory impairment should be regarded as an important tool to inform the decision process.
Classification of evidence: This study provides Class III evidence that central olfactory dysfunction identifies patients with TBI who have intracranial radiographic abnormalities with a sensitivity of 35% (95% CI 20.6%–51.7%) and specificity of 100% (95% CI 97.7%–100.0%).
GLOSSARY
- CI=
- confidence interval;
- ISS=
- injury severity score;
- TBI=
- traumatic brain injury;
- UPSIT=
- University of Pennsylvania Smell Identification Test
Footnotes
The views expressed in this manuscript do not necessarily reflect the official position of the U.S. Department of Defense or any of the institutions with which the authors are affiliated.
Go to Neurology.org for full disclosures. Funding information and disclosures deemed relevant by the authors, if any, are provided at the end of the article. The Article Processing Charge was paid by the U.S. Department of Defense Combat Casualty Care Medical Research and Development Program.
Supplemental data at Neurology.org
- Received August 29, 2014.
- Accepted in final form January 5, 2015.
- © 2015 American Academy of Neurology
This is an open access article distributed under the terms of the Creative Commons Attribution-Noncommercial No Derivative 3.0 License, which permits downloading and sharing the work provided it is properly cited. The work cannot be changed in any way or used commercially.
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