Olfactory identification and white matter integrity in amnestic mild cognitive impairment: A preliminary study

Increasing evidence suggests that olfactory impairment is associated with an increased risk of conversion from mild cognitive impairment (MCI) to Alzheimer's disease. This study was to explore how olfactory identification relates to white matter (WM) integrity, using diffusion tensor imaging (DTI) in individuals with amnestic MCI. DTI was performed from nineteen individuals with amnestic MCI (mean age: 69.95 ± 8.20 years). Olfactory identification was assessed using the Cross-Cultural Smell Identification Test (CC-SIT), a widely used test for odor identification involving a scratch and sniff test of 12 micro-encapsulated odorants. Cross-sectional voxel-wise analyses of relationships between CC-SIT scores and DTI indices were performed using Tract-Based Spatial Statistics. Higher CC-SIT scores were associated with lower mean, axial and radial diffusivities in areas such as the body and splenium of corpus callosum, frontal WM (lateral orbitofrontal, caudal middle frontal, precentral, left superior frontal, and right pars opercularis), right superior longitudinal fasciculus, anterior and superior corona radiata, and internal and external capsules, while CC-SIT scores were not significantly associated with fractional anisotropy across all MCI participants. In individuals with amnestic MCI, impaired olfactory identification is associated with alterations in WM integrity expressed as a lower diffusivities value. This cross-sectional preliminary study suggests that olfactory impairment contributes to WM microstructural alterations in individuals with amnestic MCI.