Olfactory dysfunction in Alzheimer's disease- and Lewy body-related cognitive impairment

Abstract

Introduction: Olfactory dysfunction is common in Alzheimer's disease- and Lewy body-related disorders, but its neural correlates have not been clearly elucidated.

Methods: We retrospectively recruited 237 patients with Alzheimer's disease-related cognitive impairment (ADCI) and 217 with Lewy body-related cognitive impairment (LBCI). They were identically evaluated using the Cross-Cultural Smell Identification Test, neuropsychological tests, and brain magnetic resonance imaging.

Results: LBCI had more severe olfactory dysfunction than ADCI. Patients with more severe cognitive dysfunction had worse olfactory function in both groups. In ADCI, lower Cross-Cultural Smell Identification Test scores correlated with a lower cortical thickness in brain regions typically affected in Alzheimer's disease, most prominently in the right parahippocampal cortex, whereas in LBCI, the scores correlated with white matter abnormalities in regions vulnerable to Lewy body, including subcortical regions of the orbitofrontal and frontoparietal cortices.

Discussion: Our results suggest that cortical atrophy in ADCI and white matter abnormalities in LBCI play important roles in olfactory dysfunction.

Keywords: Alzheimer's disease; Cognitive impairment; Cortical atrophy; Dementia with Lewy bodies; Olfaction; Parkinson's disease.