• Michael S Xydakis, Lisa P Mulligan, Alice B Smith, Cara H Olsen, Dina M Lyon, and Leonardo Belluscio.
• From Otorhinolaryngology/Head & Neck Surgery (M.S.X.), Neurosurgery (L.P.M.), and Neuroradiology (A.B.S.), Walter Reed National Military Medical Center, Bethesda; Traumatic Brain Injury Surgical Research Program (M.S.X., L.P.M., D.M.L.), Otorhinolaryngology/Head & Neck Surgery (M.S.X.), Neurosurgery (L.P.M.), Neuroradiology (A.B.S.), Preventive Medicine & Biostatistics (C.H.O.), Uniformed Services University (M.S.X., L.P.M., A.B.S., D.M.L.), Bethesda; and Neurological Disorders and Stroke (L.B.), National Institutes of Health, Bethesda, MD. michael.xydakis@usuhs.edu.
• Neurology. 2015 Apr 14; 84 (15): 1559-67.

ObjectiveTo 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.MethodsWe 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.ResultsOlfactometric 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.ConclusionQuantitative 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 EvidenceThis 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%).© 2015 American Academy of Neurology.

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