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Advanced Neurology Brain regions in olfactory dysfunction in PD

associated with PD, olfactory dysfunction is one of the of detecting even minor variations in brain volume or
most prevalent. 1-3 density. 20-23
Studies have shown that over 95% of individuals with The goal of this study is to explore the relationship
PD experience a notable decline in olfactory function, between olfactory dysfunction and GMV in PD, with a
which can have a significant impact on their daily lives. focus on comparing individuals with and without olfactory
Unfortunately, the importance of olfaction in enhancing dysfunction.
the quality of life and the capacity to derive pleasure
is frequently overlooked. Onset age, therapeutic 2. Materials and methods
4,5
intervention, treatment duration, and disease severity do 2.1. Subjects
not have an impact on olfactory dysfunction. 1,6,7
This study was conducted on 182 subjects, including
Neural responses to olfactory stimuli are transmitted 92 patients with PD (23 with normal smell [PD-NS] and
from the nasal epithelium to the olfactory bulb, then to the 69 with smell disorder [PD-SD]) and 90 healthy controls
olfactory cortex along with its primary connections within [HCs] from July 29, 2024, to December 13, 2024. A 3-week
the brain. The anterior olfactory nucleus, olfactory interval separated the first study visit and the follow-up
8,9
tubercle, pyriform cortex, amygdala, and entorhinal visit. Informed consent was obtained from all subjects.
cortex comprise the olfactory cortex, each receiving input
from neurons in the olfactory bulb. The pyriform cortex, The exclusion criteria were as follows: individuals
divided into anterior and posterior segments, serves as the diagnosed with various neurological conditions
primary output region for projections from the olfactory (e.g., stroke), Parkinsonism syndromes (e.g., progressive
bulb. Odorant identity is encoded in the anterior pyriform supranuclear palsy, multiple system atrophy, and uncommon
cortex, while the posterior pyriform cortex encodes motor and non-motor symptoms), psychological disorders
odor quality. The entorhinal cortex is connected to the (e.g., severe depression), individuals for whom magnetic
10
hippocampus, and its dysfunction can have an impact on resonance imaging (MRI)’s results were contraindicated,
the ability to remember and distinguish between different and cases in which any form of artifact on MRI hindered
odors. 11,12 The orbitofrontal cortex represents a significant accurate volumetric analysis.
olfactory pathway extending beyond the olfactory cortex. The HCs did not exhibit any neurological conditions,
Despite its importance, the precise function of this brain such as stroke, brain tumors, or severe mental disorders.
region in olfaction remains unclear. Studies have linked Furthermore, they reported no cognitive complaints.
it to tasks such as distinguishing between different odors, To control for potential confounding effects of age,
recognizing smells, and regulating olfactory attention. 13-15 gender, and educational level on the outcomes, participants
Lewy bodies have been observed in the olfactory bulb, in the HC group were meticulously matched with those
entorhinal cortex, and pyriform cortex during post- in the PD groups based on these covariate variables. To
mortem examinations of individuals with PD. 14,15 minimize potential confounders, such as cognitive status
The present study aims to investigate the relationship and medication, the cognitive status of the patients was
between olfactory dysfunction and gray matter volume evaluated using the Montreal Cognitive Assessment, and no
(GMV) using voxel-based morphometry (VBM). VBM significant differences were found between the two groups.
is capable of examining and assessing the structural In addition, only the L-dopa-carbidopa combination
alterations in brain areas affected by neurodegenerative treatment was used for the patients in this study, and the
disorders, such as dementia, PD, and multiple sclerosis. 16-18 effect of this variable is similar in both groups.
The software (Computational Anatomy Toolbox [CAT],
Structural Brain Mapping Group, Germany) was initially 2.2. Olfactory assessments
suggested and adopted as the norm by Ashburner and In the present study, the Iran Smell Identification Test
Friston VBM automatically assesses the volume of each (ISIT), a standard 24-item odor identification test, was
19
voxel within the segmented tissues to detect differences used to evaluate the olfactory performance of PD and
that suggest gray matter (GM) atrophy or localized HC groups according to cultural adaptation. A score of
alterations in white matter (WM) density. Consequently, 0 to 18 in this test indicates a smell disorder, while 19 to
VBM remains impartial regarding structural changes in 24 indicates normal smell. Baseline demographic and
24
specific brain regions, circumventing subjective variations clinical data, including age, gender, educational level, and
introduced by the artificial delineation of regions of disease duration, were documented. To develop the ISIT,
interest. It offers an objective and thorough assessment of researchers adapted the University of Pennsylvania Smell
anatomical changes throughout the entire brain, capable Identification Test (UPSIT) for the Iranian population.

Volume 4 Issue 3 (2025) 61 doi: 10.36922/AN025110024