Abstract
Background: Olfactory dysfunction is associated with Alzheimer’s disease
(AD), and already present at pre-dementia stage.
Objectives: Based on the assumption that early neurodegeneration in AD is
asymmetrical and that olfactory input is primarily processed in the ipsilateral
hemisphere, we assessed whether unirhinal psychophysical and electrophysiological
assessment of olfactory function can contribute to the diagnostic workup of mild cognitive
impairment (MCI).
Methods: Olfactory function of 13 MCI patients with positive amyloid PET, 13
aged-matched controls (AC) with negative amyloid PET and 13 patients with post-infectious
olfactory loss (OD) was assessed unirhinally using (1) psychophysical testing of olfactory
detection, discrimination and identification performance and (2) the recording of
olfactory event-related brain potentials. Time-frequency analysis was used to enhance the
signal-to-noise ratio of the electrophysiological responses. Psychophysical and
electrophysiological assessment of auditory and trigeminal chemosensory function served as
controls.
Results: As compared to AC and OD, MCI patients exhibited a significant
asymmetry of olfactory performance. This asymmetry efficiently discriminated between MCI
and AC (sensitivity: 85% , specificity: 77% ), as well as MCI and OD (sensitivity: 85% ,
specificity: 70% ). There was also an asymmetry of the electrophysiological responses, but
not specific for MCI. In both MCI and OD, olfactory stimulation of the best nostril
elicited significantly more activity than stimulation of the worse nostril, between
3–7.5 Hz and 1.2–2.0 s after stimulus onset. Trigeminal and auditory psychophysical
testing did not show any difference between groups.
Conclusion: MCI patients exhibit a marked asymmetry of behavioral olfactory
function, which could be useful for the diagnostic workup of MCI.
