Association between Olfactory Deficit and Motor and Cognitive Function in Parkinson's Disease

Area of Science:

• Neurology
• Neuroscience
• Olfactory Research

Background:

• Olfactory dysfunction is a common non-motor symptom in Parkinson's disease (PD).
• The relationship between baseline olfactory function and the progression of motor and cognitive impairments in PD remains incompletely understood.

Purpose of the Study:

• To determine if baseline olfactory dysfunction in drug-naïve Parkinson's disease patients correlates with their initial and long-term motor and cognitive status.
• To explore the prognostic value of olfactory impairment in Parkinson's disease progression.

Main Methods:

• Recruited 228 drug-naïve Parkinson's disease patients for a mean 6-year follow-up.
• Assessed baseline olfaction using the Cross-Cultural Smell Identification Test (CCSIT), alongside neuropsychological testing and DaTscan PET imaging.
• Categorized olfactory function into normosmia, hyposmia, and anosmia; monitored changes in levodopa-equivalent dose (LED), motor complications, and dementia conversion.

Main Results:

• 80.7% of PD patients had hyposmia and 26.1% had anosmia at diagnosis.
• Baseline olfactory dysfunction did not correlate with initial motor symptoms or longitudinal changes in LED and motor complications.
• Anosmic patients showed poorer baseline performance on naming and executive function tests and had a significantly higher rate of dementia conversion compared to normosmic and hyposmic groups.

Conclusions:

• Baseline olfactory dysfunction in Parkinson's disease is not associated with motor deficits but is linked to cognitive impairment and poorer prognosis.
• Severe olfactory impairment may indicate early cortical involvement, potentially in frontotemporal regions.
• The findings suggest that olfactory testing could serve as a potential early biomarker for cognitive decline and disease progression in Parkinson's disease.