Objective: To examine the association between motor subtypes’ stability and cognitive assessment scores across three years in early Parkinson’s disease (PD).

Background: Past studies have explored the relationships between PD motor subtypes and markers, such as non-motor symptoms, motor scores and cognition. However, there is limited literature on the stability of PD motor subtypes and their correlations with cognition.

Method: 105 early PD patients from the Early PD Longitudinal Singapore Study (PALS) were grouped based on motor subtype stability: tremor-dominant stable (N=50), postural instability and gait difficulty stable (N=10) and non-stable (N=45). Subtypes were classified according to the Movement Disorder Society’s Unified PD Rating Scale (MDS-UPDRS) criteria. A repeated measures linear model was run to determine the interaction between subtype stability and cognitive scores across 3 years while controlling for age, gender, education, baseline LEDD and MDS-UPDRS III.

Results: There was no significant association of subtype stability nor interaction effect with time on overall cognitive measures. There was a significant association of subtype stability on

Attention–Symbol Span (F[95,2]=3.81, p=0.026), with stable subtypes performing better but without significant association at pairwise comparison. Contrary to hypothesis, there was a significant individual effects of time on cognitive measures, with improved scores on ADAS-Cog Delayed (MD=-0.673, p=0.004), Symbol Span (MD=-3.34, p=0.006) and Boston Naming (MD=-0.803, p=0.028) between year 1 and 2; Boston Naming (MD=-0.986, p=0.005) and RBANS Line Orientation (MD=-1.02, p=0.006) between year 1 and 3; and RBANS Line Orientation (MD=-0.941, p=0.012) between year 2 and 3.

Conclusion: There was no significant correlation between motor subtype stability and cognitive scores over 3 years in early PD. Improved scores on several cognitive assessments were found

over time across all subtype stability groups. This may be due to practice effect as cognitive tests were done at one-year interval. Moreover, as disease progression may not be drastic in the first 3 years, most patients should still be cognitively intact for practice effect to set in. This can serve as a consideration for future clinical research to set longer intervals between cognitive tests and further this research beyond 5 years when patients enter the later stages of PD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/motor-subtype-stability-and-cognitive-profiles-in-early-parkinsons-disease/