Olfactory Impairment May Indicate TBI Among Blast-Injured Troops

Decreased ability to identify odors may be a marker of acute structural neuropathology resulting from trauma, according to research published online ahead of print March 18 in Neurology. Quantitative identification olfactometry has limited sensitivity but high specificity in detecting this pathology and could inform decisions about whether advanced neuroimaging is required, said the authors.

Michael S. Xydakis, MD, a colonel in the US Air Force and Associate Professor of Surgery at the Uniformed Services University of the Health Sciences in Bethesda, Maryland, and colleagues enrolled 231 consecutive patients with polytrauma in a study to determine whether a quantitative assessment of differential olfactory performance could serve as a reliable antecedent marker for the preclinical detection of intracranial neurotrauma. Participants had been acutely injured from explosions during combat operations in Afghanistan or Iraq, required immediate stateside evacuation, and were enrolled prospectively during two and a half years.

All patients underwent evaluation for possible traumatic brain injury (TBI). The investigators stratified the patients into groups according to severity of TBI and neuroimaging results. Blast-injured troops without TBI who had comparable demographic features and severity of polytrauma formed the comparison control group. An otorhinolaryngologist administered the University of Pennsylvania Smell Identification Test to each patient. Patients were described as having normal, decreased, or absent olfactory function, and the latter two categories were considered to represent olfactory impairment.

Impairment Associated With Frontal and Temporal Lobe Injuries
Approximately 6% of participants had impaired olfactory function. All patients in the mild TBI group and the blast-injured control group had normal olfactory function. Median olfactometric scores did not differ significantly between these two groups. All participants with normal neuroimaging, including 127 patients with mild TBI and 47 controls, had normal olfactory function.

Among the 40 patients with abnormal imaging, 35% had olfactory impairment. Data analysis indicated that olfactometric score predicted abnormal neuroimaging significantly better than chance alone. Olfactory testing was administered to 18 of the patients with abnormal imaging within 14 days after injury. Nine of these patients had impaired function. The remaining 22 soldiers with abnormal imaging underwent testing 15 or more days after injury, and five of them had impaired function. “These results suggest that it is worth testing the hypothesis that sensitivity of olfactory testing to identify patients with structural brain injury may be higher if testing is performed closer to the time of injury,” said Dr. Xydakis.

Approximately 79% of patients with olfactory impairment had injury to the frontal lobe, compared with 42% of patients with normal olfactory function. About 86% of troops with olfactory impairment had either frontal or temporal involvement, compared with 50% of patients with normal function. Approximately 36% of troops with olfactory impairment had both frontal and temporal involvement, compared with 12% of patients with normal function.

Test May Detect Injury Preclinically
“The radiographic findings support a higher-order CNS etiology for the observed impairment,” said Dr. Xydakis. The inclusion of the blast-injured control group with normal olfactometric scores may mitigate the concern that observed impairments resulted from peripheral trauma at the intranasal receptor level.

The finding that only troops with concurrent acute traumatic radiographic abnormalities had olfactory impairment “supports the assertion that impaired olfactory identification is only present in the context of significant intracranial neurotrauma,” he added. “Ultimately, it is the radiographic presence and the radiographic locations of the structural brain injuries that define the probability of subsequent olfactory performance degradation, and not simply the abstract and unquantifiable risk factor of a ‘blow or hit to the head region.’

“The presence of measurable abnormalities with central olfactory dysfunction provides added value to the practicing physician for preclinical detection of intracranial injury and, accordingly, subsequent disease-modifying early interventions,” Dr. Xydakis continued. “While the level of sensitivity for screening purposes is insufficient to exclude all types of post-traumatic neuropathology, the absolute specificity and the association with frontal or temporal lobe injury enhance its value in clinical practice.”

—Erik Greb

Decreased ability to identify odors may be a marker of acute structural neuropathology resulting from trauma, according to research published online ahead of print March 18 in Neurology. Quantitative identification olfactometry has limited sensitivity but high specificity in detecting this pathology and could inform decisions about whether advanced neuroimaging is required, said the authors.

Michael S. Xydakis, MD, a colonel in the US Air Force and Associate Professor of Surgery at the Uniformed Services University of the Health Sciences in Bethesda, Maryland, and colleagues enrolled 231 consecutive patients with polytrauma in a study to determine whether a quantitative assessment of differential olfactory performance could serve as a reliable antecedent marker for the preclinical detection of intracranial neurotrauma. Participants had been acutely injured from explosions during combat operations in Afghanistan or Iraq, required immediate stateside evacuation, and were enrolled prospectively during two and a half years.

All patients underwent evaluation for possible traumatic brain injury (TBI). The investigators stratified the patients into groups according to severity of TBI and neuroimaging results. Blast-injured troops without TBI who had comparable demographic features and severity of polytrauma formed the comparison control group. An otorhinolaryngologist administered the University of Pennsylvania Smell Identification Test to each patient. Patients were described as having normal, decreased, or absent olfactory function, and the latter two categories were considered to represent olfactory impairment.

Impairment Associated With Frontal and Temporal Lobe Injuries
Approximately 6% of participants had impaired olfactory function. All patients in the mild TBI group and the blast-injured control group had normal olfactory function. Median olfactometric scores did not differ significantly between these two groups. All participants with normal neuroimaging, including 127 patients with mild TBI and 47 controls, had normal olfactory function.

Among the 40 patients with abnormal imaging, 35% had olfactory impairment. Data analysis indicated that olfactometric score predicted abnormal neuroimaging significantly better than chance alone. Olfactory testing was administered to 18 of the patients with abnormal imaging within 14 days after injury. Nine of these patients had impaired function. The remaining 22 soldiers with abnormal imaging underwent testing 15 or more days after injury, and five of them had impaired function. “These results suggest that it is worth testing the hypothesis that sensitivity of olfactory testing to identify patients with structural brain injury may be higher if testing is performed closer to the time of injury,” said Dr. Xydakis.

Approximately 79% of patients with olfactory impairment had injury to the frontal lobe, compared with 42% of patients with normal olfactory function. About 86% of troops with olfactory impairment had either frontal or temporal involvement, compared with 50% of patients with normal function. Approximately 36% of troops with olfactory impairment had both frontal and temporal involvement, compared with 12% of patients with normal function.

Test May Detect Injury Preclinically
“The radiographic findings support a higher-order CNS etiology for the observed impairment,” said Dr. Xydakis. The inclusion of the blast-injured control group with normal olfactometric scores may mitigate the concern that observed impairments resulted from peripheral trauma at the intranasal receptor level.

The finding that only troops with concurrent acute traumatic radiographic abnormalities had olfactory impairment “supports the assertion that impaired olfactory identification is only present in the context of significant intracranial neurotrauma,” he added. “Ultimately, it is the radiographic presence and the radiographic locations of the structural brain injuries that define the probability of subsequent olfactory performance degradation, and not simply the abstract and unquantifiable risk factor of a ‘blow or hit to the head region.’

“The presence of measurable abnormalities with central olfactory dysfunction provides added value to the practicing physician for preclinical detection of intracranial injury and, accordingly, subsequent disease-modifying early interventions,” Dr. Xydakis continued. “While the level of sensitivity for screening purposes is insufficient to exclude all types of post-traumatic neuropathology, the absolute specificity and the association with frontal or temporal lobe injury enhance its value in clinical practice.”

—Erik Greb

Decreased ability to identify odors may be a marker of acute structural neuropathology resulting from trauma, according to research published online ahead of print March 18 in Neurology. Quantitative identification olfactometry has limited sensitivity but high specificity in detecting this pathology and could inform decisions about whether advanced neuroimaging is required, said the authors.

Michael S. Xydakis, MD, a colonel in the US Air Force and Associate Professor of Surgery at the Uniformed Services University of the Health Sciences in Bethesda, Maryland, and colleagues enrolled 231 consecutive patients with polytrauma in a study to determine whether a quantitative assessment of differential olfactory performance could serve as a reliable antecedent marker for the preclinical detection of intracranial neurotrauma. Participants had been acutely injured from explosions during combat operations in Afghanistan or Iraq, required immediate stateside evacuation, and were enrolled prospectively during two and a half years.

All patients underwent evaluation for possible traumatic brain injury (TBI). The investigators stratified the patients into groups according to severity of TBI and neuroimaging results. Blast-injured troops without TBI who had comparable demographic features and severity of polytrauma formed the comparison control group. An otorhinolaryngologist administered the University of Pennsylvania Smell Identification Test to each patient. Patients were described as having normal, decreased, or absent olfactory function, and the latter two categories were considered to represent olfactory impairment.

Impairment Associated With Frontal and Temporal Lobe Injuries
Approximately 6% of participants had impaired olfactory function. All patients in the mild TBI group and the blast-injured control group had normal olfactory function. Median olfactometric scores did not differ significantly between these two groups. All participants with normal neuroimaging, including 127 patients with mild TBI and 47 controls, had normal olfactory function.

Among the 40 patients with abnormal imaging, 35% had olfactory impairment. Data analysis indicated that olfactometric score predicted abnormal neuroimaging significantly better than chance alone. Olfactory testing was administered to 18 of the patients with abnormal imaging within 14 days after injury. Nine of these patients had impaired function. The remaining 22 soldiers with abnormal imaging underwent testing 15 or more days after injury, and five of them had impaired function. “These results suggest that it is worth testing the hypothesis that sensitivity of olfactory testing to identify patients with structural brain injury may be higher if testing is performed closer to the time of injury,” said Dr. Xydakis.

Approximately 79% of patients with olfactory impairment had injury to the frontal lobe, compared with 42% of patients with normal olfactory function. About 86% of troops with olfactory impairment had either frontal or temporal involvement, compared with 50% of patients with normal function. Approximately 36% of troops with olfactory impairment had both frontal and temporal involvement, compared with 12% of patients with normal function.

Test May Detect Injury Preclinically
“The radiographic findings support a higher-order CNS etiology for the observed impairment,” said Dr. Xydakis. The inclusion of the blast-injured control group with normal olfactometric scores may mitigate the concern that observed impairments resulted from peripheral trauma at the intranasal receptor level.

The finding that only troops with concurrent acute traumatic radiographic abnormalities had olfactory impairment “supports the assertion that impaired olfactory identification is only present in the context of significant intracranial neurotrauma,” he added. “Ultimately, it is the radiographic presence and the radiographic locations of the structural brain injuries that define the probability of subsequent olfactory performance degradation, and not simply the abstract and unquantifiable risk factor of a ‘blow or hit to the head region.’

“The presence of measurable abnormalities with central olfactory dysfunction provides added value to the practicing physician for preclinical detection of intracranial injury and, accordingly, subsequent disease-modifying early interventions,” Dr. Xydakis continued. “While the level of sensitivity for screening purposes is insufficient to exclude all types of post-traumatic neuropathology, the absolute specificity and the association with frontal or temporal lobe injury enhance its value in clinical practice.”

—Erik Greb