Olfactory Function and Diffusion Tensor Imaging as Markers of Mild Cognitive Impairment in Early Stages of Parkinson's Disease

Abstract

Parkinson's disease (PD) is a neurodegenerative disorder that is typified by motor signs and symptoms but can also lead to significant cognitive impairment and dementia Parkinson's Disease Dementia (PDD). While dementia is considered a nonmotor feature of PD that typically occurs later, individuals with PD may experience mild cognitive impairment (PD-MCI) earlier in the disease course. Olfactory deficit (OD) is considered another nonmotor symptom of PD and often presents even before the motor signs and diagnosis of PD. We examined potential links among cognitive impairment, olfactory functioning, and white matter integrity of olfactory brain regions in persons with early-stage PD. Cognitive tests were used to established groups with PD-MCI and with normal cognition (PD-NC). Olfactory functioning was examined using the University of Pennsylvania Smell Identification Test (UPSIT) while the white matter integrity of the anterior olfactory structures (AOS) was examined using magnetic resonance imaging (MRI) diffusion tensor imaging (DTI) analysis. Those with PD-MCI demonstrated poorer olfactory functioning and abnormalities based on all DTI parameters in the AOS, relative to PD-NC individuals. OD and microstructural changes in the AOS of individuals with PD may serve as additional biological markers of PD-MCI.

Olfactory Impairment Correlates with Executive Functions Disorders and Other Specific Cognitive Dysfunctions in Parkinson’s Disease

“…Both olfactory deficits and cognitive impairment represent well known non-motor disorders in PD [1,5]; moreover, the cognitive impairment may progress in dementia during the course of the disease in a substantial number of patients [5,27]. In this context, a recent study of Fang and colleagues [11] showed more severe anosmia in PD patients with cognitive impairment using University of Pennsylvania Smell Identification Test (UPSIT) and the MoCA scale.…”

The Value of Subjective Olfactometry as a Predictive Biomarker of Neurodegenerative Diseases: A Systematic Review

“…They only found a correlation between ODs and motor and non-motor impairment in the TDPD group. Stewart et al [ 36 ] reported worse smell scores and higher MRI-based impairment in patients with MCI and PD compared with those with normal cognition, in proportion to the severity of symptoms.…”

“…In PD, most of the studies reviewed described greater smell dysfunction in ND patients than in controls, thus suggesting olfactory impairment as a disease’s risk factor [ 17 , 26 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 44 , 45 , 46 ]. The mean prevalence of olfactory impairment in PD was 83.8 ± 14.5 across eleven studies, with some of them reporting a negative correlation between olfactometry outcomes and disease impairment [ 28 , 30 ].…”

“…Moreover, diffusion tensor imaging (DTI) showed that PD patients with MCI and poorer olfactory outcomes exhibit more microstructural abnormalities than PD patients with no cognitive decline [ 36 ]. In addition, dopamine transporter single-photon emission computed tomography (DaT-SPECT) also explained that the high prevalence of olfactory loss in PD patients, as measured by the UPSIT, is due to the association of ODs with the pronounced loss of nigrostriatal dopamine neurons in the putamen and caudate nucleus [ 36 ]. Therewithal, more studies should investigate the association between atrophy degree in regions of interest in relation to ODs and other overlapping comorbidities.…”

Special Issue: Mild Cognitive Impairment

“…They note that NIBS has beneficial modifying effects on cellular neuroplasticity, which could be combined with neuroimaging, electrophysiology and cognitive therapy in prospective long-term clinical studies. Stewart et al 9 compared PDMCI subjects with PD patients demonstrating normal cognition (PDNC). They found that the PDMCI group had poorer olfactory function, measured by smell tests.…”