Olfactory Network Functional Connectivity as a Marker for Parkinson's Disease Severity

Area of Science:

• Neuroscience
• Neurology
• Olfactory Research

Background:

• Olfactory impairment is a common non-motor symptom in Parkinson's disease (PD).
• PD is clinically heterogeneous, with distinct motor subtypes like akinetic-rigid (PD_AR) and tremor-predominant (PD_T).
• The relationship between PD motor subtypes and olfactory network dysfunction remains unclear.

Purpose of the Study:

• To investigate olfactory function and olfactory network (ON) connectivity in PD_AR and PD_T subtypes.
• To compare olfactory performance and brain connectivity between PD subtypes and cognitively normal (CN) individuals.
• To explore the potential of olfactory impairment as a marker for PD severity.

Main Methods:

• Olfactory function was assessed using the University of Pennsylvania Smell Identification Test (UPSIT).
• Resting-state functional magnetic resonance imaging (rs-fMRI) was used to analyze seed-based functional connectivity (FC) of the olfactory network.
• Participants included 17 PD_AR, 15 PD_T, and 24 CN individuals, matched for age and cognition.

Main Results:

• PD_AR patients exhibited significantly lower UPSIT scores compared to PD_T patients.
• Reduced ON functional connectivity (FC) was observed in PD_AR compared to both PD_T and CN groups.
• Specific differences in FC were found in the primary olfactory cortex, orbitofrontal cortex, insula, hippocampus, and posterior cingulate cortex between PD subtypes and CN.

Conclusions:

• Distinct olfactory network functional connectivity patterns characterize akinetic-rigid and tremor-predominant Parkinson's disease subtypes.
• Olfactory performance correlates with motor subtypes and ON connectivity, suggesting a neural basis for olfactory deficits in PD.
• Olfactory impairment may serve as a potential clinical marker for Parkinson's disease severity, particularly in the akinetic-rigid subtype.