Odor Identification and Regional Gray Matter Atrophy in Patients with Alzheimer's Disease, Parkinson's Disease, and the Healthy Elderly: A Cross-Sectional Structural MRI Study.

Simonas Jesmanas,Rymantė Gleiznienė,Daiva Rastenytė,Mindaugas Baranauskas,Vaidas Matijošaitis

doi:10.3390/brainsci11101296

Simonas Jesmanas, Rymantė Gleiznienė + Show 3 more

Open Access

https://doi.org/10.3390/brainsci11101296

Copy DOI

Abstract

Multiple associations between impaired olfactory performance and regional cortical and deep gray matter atrophy have been reported in separate studies of patients with Alzheimer’s disease (AD), Parkinson’s disease (PD), and of the healthy elderly. We aimed to evaluate such possible associations among these populations in a unified manner. Twenty AD, twenty PD patients’ and twenty healthy age- and sex-matched controls’ odor identification performance was assessed with the Lithuanian adaptation of the Sniffin’ Sticks 12 odor identification test, followed by morphometric gray matter analysis by MRI using FreeSurfer. AD patients had significantly lower cognitive performance than both PD patients and the healthy elderly, as evaluated with the Mini-Mental State Examination (MMSE). Odor identification performance was significantly worse in AD and PD patients compared with the healthy elderly; AD patients performed slightly worse than PD patients, but the difference was not statistically significant. Among patients with AD, worse odor identification performance was initially correlated with atrophy of multiple cortical and deep gray matter regions known to be involved in olfactory processing, however, only two measures—decreased thicknesses of the right medial and left lateral orbitofrontal cortices—remained significant after adjustment for possible confounders (age, MMSE score, and global cortical thickness). Among patients with PD and the healthy elderly we found no similar statistically significant correlations. Our findings support the key role of the orbitofrontal cortex in odor identification among patients with AD, and suggest that correlations between impaired odor identification performance and regional gray matter atrophy may be relatively more pronounced in AD rather than in PD.

Highlights

Olfactory function can be divided into odor detection, discrimination, and identification [1,2]
Cognitive impairment and neurodegenerative diseases negatively influence olfactory function: Alzheimer’s disease (AD) significantly impairs higher-order olfactory processing with a slightly weaker effect on lower-order olfactory processes, while Parkinson’s disease (PD) impairs both higher-order and lower-order olfactory processes more homogenously; deficits in odor detection are relatively more evident in patients with PD [1,6,7]. This slightly different nature of olfactory dysfunction can be in part explained by the greater cognitive and semantic deficits noted in most cases of AD, which may contribute to preferential impairment of higher-order olfactory processing rather than the cognitively simpler odor detection [1,6]
While the age of AD and PD groups did not differ significantly compared with control subjects, AD patients were significantly older than PD patients (72.3 and 64.1 years, respectively; p = 0.012)

Summary

Introduction

Olfactory function can be divided into odor detection, discrimination, and identification [1,2]. Cognitive impairment and neurodegenerative diseases negatively influence olfactory function: Alzheimer’s disease (AD) significantly impairs higher-order olfactory processing (odor discrimination and identification) with a slightly weaker effect on lower-order olfactory processes (odor detection), while Parkinson’s disease (PD) impairs both higher-order and lower-order olfactory processes more homogenously; deficits in odor detection are relatively more evident in patients with PD [1,6,7] This slightly different nature of olfactory dysfunction can be in part explained by the greater cognitive and semantic deficits noted in most cases of AD, which may contribute to preferential impairment of higher-order olfactory processing rather than the cognitively simpler odor detection [1,6]. Other causes of impaired olfaction include upper respiratory tract infections, sinonasal disease, and head trauma [10]

Objectives

Methods

Results

Conclusion