Odor identification deficit in mild cognitive impairment and Alzheimer's disease is associated with hippocampal and deep gray matter atrophy

Even in early stages, Alzheimer's disease (AD) is associated with olfactory deficit. We assess the association of volumetric differences in subcortical deep gray matter (DGM) structures and odor identification deficit (OID) in subjects with amnestic mild cognitive impairment (aMCI), AD and normal controls (NCs), and relate findings to the current gold standard right sided memory measure, visual reproduction. Eighty subjects (19 aMCI; 42 CE; 19 NC) were included in this study. We obtained olfactory testing and normalized structural brain volumes from 3T T1 MRI scans. Associations between MRI, olfactory- and memory impairment were studied using Pearson- and partial-correlation adjusted for age. AD patients had significantly higher olfactory deficits, lower visual reproduction scores, and reduced brain volumes (p<0.05). Within aMCI, OID was associated with lower right hippocampal- and left amygdala volume (p<0.05). In AD, OID was associated with bilaterally lower hippocampus and left amygdala volumes. In contrast, visual reproduction was associated with bilateral volume loss regardless of study group. OID is a more specific marker of early pathological right mesial-temporal involvement than the currently regarded gold standard of right sided-memory (visual reproduction). OID may be valuable in the longitudinal evaluation of disease modifying treatments in early disease course.