Olfactory identification in amnestic and non-amnestic mild cognitive impairment and its neuropsychological correlates

Background: Olfactory identification impairment in amnestic mild cognitive impairment (aMCI) patients is well documented and considered to be caused by underlying Alzheimer's disease (AD) pathology, contrasting with less clear evidence in non-amnestic MCI (naMCI). The aim was to (a) compare the degree of olfactory identification dysfunction in aMCI, naMCI, controls and mild AD dementia and (b) assess the relation between olfactory identification and cognitive performance in aMCI compared to naMCI. Methods: 75 patients with aMCI and 32 with naMCI, 26 patients with mild AD and 27 controls underwent the multiple choice olfactory identification Motol Hospital Smell Test with 18 different odors together with a comprehensive neuropsychological examination. Results: Controlling for age and gender, patients with aMCI and naMCI did not differ significantly in olfactory identification and both performed significantly worse than controls (p < 0.001), albeit also better than patients with mild AD (p < .001). In the aMCI group, higher scores on MMSE, verbal and non-verbal memory and visuo-spatial tests were significantly related to better olfactory identification ability. Conversely, no cognitive measure was significantly related to olfactory performance in naMCI. Conclusion: Olfactory identification is similarly impaired in aMCI and naMCI. Olfactory impairment is proportional to cognitive impairment in aMCI but not in naMCI. (C) 2015 Published by Elsevier B.V.