Semantic fluency and processing speed are reduced in non-cognitively impaired participants with Parkinson’s disease

ABSTRACT

Introduction: Parkinson’s disease (PD) is associated with a range of cognitive deficits. Few studies have carefully examined the subtle impacts of PD on cognition among patients who do not meet formal criteria for MCI or dementia. The aim of the current study was thus to describe the impact of PD on cognition in those without cognitive impairment in a well-characterized cohort.

Methods: Non-cognitively impaired participants (122 with PD, 122 age- and sex-matched healthy volunteers) underwent extensive cognitive testing. Linear regression analyses compared diagnostic group performance across cognitive measures. For cognitive tasks that were significantly different between groups, additional analyses examined group differences restricting the group inclusion to PD participants with mild motor symptoms or disease duration less than 10 years.

Results: Processing speed and semantic verbal fluency were significantly lower in the PD group (B = −3.77, 95% CIs [−5.76 to −1.77], p < .001, and B = −2.02, 95% CIs [−3.12, −0.92], p < .001, respectively), even after excluding those with moderate to severe motor symptoms (B = −2.73, 95% CIs [−4.94 to −0.53], p = .015 and B = −2.11, 95% CIs [−3.32 to −0.91], p < .001, respectively) or longer disease duration (B = −3.89, 95% CIs [−6.14 to −1.63], p < .001 and B = −1.58, 95% CIs [−2.78 to −0.37], p = .010, respectively). Semantic verbal fluency remained significantly negatively associated with PD diagnosis after controlling for processing speed (B = −1.66, 95% CIs [−2.79 to −0.53], p = .004).

Conclusions: Subtle decline in specific cognitive domains may be present among people diagnosed with PD but without evidence to support a formal cognitive diagnosis. These results suggest the importance of early awareness of the potential for diminishing aspects of cognition in PD even among those without mild cognitive impairment or dementia.

KEYWORDS:

• Aging
• cognition
• healthy volunteers
• neuropsychological assessment
• Parkinson’s disease

Acknowledgments

This work was supported by the National Institutes of Neurological Disorders and Stroke grant P50 NS062684, Department of Veterans Affairs grant 101 CX001702, and the Scully Initiative Fund. L.S.R. and T.M.D were supported by P50 NS38377 and U01 NS082133. The funding sources did not provide scientific input for the study. This material is the result of work supported with resources and the use of facilities at the Veterans Affairs Puget Sound Health Care System. We sincerely thank our research participants for their participation in this study.

Disclosure statment

No potential conflict of interest was reported by the author(s).

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Additional information

Funding

This work was supported by the National Institute of Neurological Disorders and Stroke grant P50 NS062684, Department of Veterans Affairs grant 101 CX001702, and the Scully Initiative Fund. L.S.R. and T.M.D were supported by P50 NS38377 and U01 NS082133.