Objective: Investigate cognitive mechanisms contributing to olfactory dysfunction in Parkinson’s disease.

Background: Accurate early diagnosis of Parkinson’s disease is hampered by its long prodromal period and the variable manifestations of its cardinal motor symptoms. Since non-motor symptoms precede the onset of motor symptoms, they are gaining more attention both to aid diagnosis and to more fully understand the underlying disease mechanisms. In particular, the presence of olfactory dysfunction is currently used as a non-disease-specific diagnostic aid for Parkinson’s disease, as substantial olfactory dysfunction can occur before the onset of motor symptoms. However, the underlying causes and mechanisms involved in olfactory dysfunction are incompletely understood.

Method: Relationships between olfactory dysfunction and cognitive assessments were evaluated using for 1,280 subjects assigned by the Parkinson’s Progression Marker’s Initiative (PPMI) into different Parkinson’s-disease diagnostic categories. Structural equation modeling was used to evaluate whether impaired global cognition (measured by the Montreal Cognitive Assessment), verbal learning and memory (measured by a Hopkins Verbal Learning Test subscore), and visuospatial/executive functioning (measured as a Montreal Cognitive Assessment subscore) each contribute to olfactory dysfunction (measured by the University of Pennsylvania Smell Identification Test score) in these diagnostic categories.

Results: When measures of global cognition and verbal learning/memory were included in the same model, only the measure of verbal learning/memory was significant in explaining olfactory dysfunction. However, when the measure of global cognition was replaced by a measure of visuospatial/executive function, it too was significant in explaining olfactory dysfunction for some of the PPMI diagnostic categories.

Conclusion: Impairment of the cognitive processes associated with verbal learning/memory and visuospatial/executive function contribute to the olfactory dysfunction seen in Parkinson’s disease.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/cognitive-processes-that-indirectly-effect-olfactory-dysfunction-in-parkinsons-disease/