What is the role of olfactory-evoked response in the diagnosis of taste and smell disorders?

Updated: Dec 11, 2018
  • Author: Eric H Holbrook, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Answer

To standardize the patient reaction to eye movements, electroencephalogram (EEG) electrodes and an electrooculogram measure olfactory-evoked potentials. A visual tracking task is performed to ensure constant alertness to the task, and headphones playing white noise are worn to mask auditory clues.

Either carbon dioxide (no odor but a trigeminal stimulant) or hydrogen sulfide is delivered via an olfactometer to the nose in a constantly flowing air stream. N1 is the first negative peak measured, and P2 is the second positive trough. Latencies are measured to these two values.

As a common testing method, olfactory-evoked responses are impractical for clinical use. In patients with neurologic disease, the UPSIT revealed abnormality more frequently than did olfactory-evoked responses.

For clinical olfactory function testing, the authors' experience is that the self-administered UPSIT test allows for practical use during a busy clinical practice. However, in the absence of the olfactory tests described above, a simple screening test using a common alcohol pad can be used. The envelope is opened at one end and presented to the patient. With the patient's eyes closed, the pad is then positioned at the level of the umbilicus and slowly brought closer to the nose. The patient is instructed to notify the tester when the alcohol is again detected. The distance of the pad from the nose correlates with the patient's olfactory ability, with a distance of less than 20 cm indicating hyposmia.


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