Objective: The aim of our study was to clarify the relationships between olfaction and cognition in Parkinson’s disease (PD) using a comprehensive neuropsychological battery.

Background: Previous attempts to describe the relationship between olfactory and cognitive impairment in Parkinson’s disease have produced varying results. While one study reported no relationship between olfaction and cognition in PD (Doty et al 1989), Bohnen et al (2010) and Postuma and Gagnon (2010) found that olfactory ability was associated with episodic memory, and Parrao et al (2010) reported an association between olfactory and executive deficits in PD.

Methods: We examined 52 patients with idiopathic Parkinson’s disease (18 women, 34 men) with mean age of 63 years (range 37-73), mean education of 13.4 years (range 7-22) and with mean Mini Mental Status Exam score of 27 (range 20-30). Mean duration of disease was 10 years (range 1-22). All patients completed a test of olfactory identification ability (University of Pennsylvania Smell Identification Test, UPSIT), as well as a comprehensive neuropsychological test battery that consisted of 14 cognitive tests yielding a total of 33 cognitive measures grouped into 8 cognitive domains: Attention, working memory, information processing speed, verbal memory, nonverbal memory, visuospatial functions, language and executive functions.

Results: We found that most cognitive measures correlated significantly with olfactory identification in PD. The only exceptions to this were the cognitive screening score (Mini Mental), language (naming) and one aspect of visuospatial functions (judgment of line orientations). However, the strength of the relationship with olfaction varied across cognitive domains. Language and visuospatial functions were insignificantly and/or weakly related to olfaction. Attention, working memory, information processing speed, executive functions and nonverbal memory were moderately associated with olfaction, while verbal episodic memory had a strong relationship with olfactory status.

Conclusions: The relationship between cognitive and olfactory impairment is complex in PD.  Our data confirmed that olfactory dysfunction is associated with cognitive measures, most strongly with episodic verbal memory and less strongly with other aspects of cognition. Whether this finding reflects overlapping test demands or a PD subtype that impairs non-motor domains require further elucidation.

References: Bohnen NI, Muller ML, Kotagal V, Koeppe RA, Kilbourn MA, Albin RL, Frey KA. Olfactory dysfunction, central cholinergic integrity and cognitive impairment in Parkinson’s disease. Brain 2010; 133: 1747–54.

Doty RL, Riklan M, Deems DA, Reynolds C, Stellar S. The Olfactory and Cognitive Deficits of Parkinson’s Disease: Evidence for Independence. Ann Neurol 1989:25: 166-171.

Parrao T, Chana P, Venegas P, Behrens MI, Aylwin ML. Olfactory Deficits and Cognitive Dysfunction in Parkinson’s Disease. Neurodegenerative Dis 2012;10:179–182.

Postuma R, Gagnon JF. Cognition and olfaction in Parkinson’s disease. Brain 2010: 133, 1-2.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-complex-relationship-between-olfactory-and-cognitive-impairment-in-parkinsons-disease/