Objective: To evaluate the stability of mild cognitive impairment in Parkinson’s disease (PD-MCI) over time to determine its clinical utility as a marker of disease.

Background: Mild cognitive impairment is common in early Parkinson’s disease (PD) and may be a risk factor or prodromal stage of developing dementia (PDD). However, the longitudinal characteristics of PD-MCI are unknown, and whether it is a stable state, likely to decline or even improve over time.

Methods: 212 newly-diagnosed PD patients were recruited into a longitudinal study and re-assessed at 18 and 36 months follow up assessments. Participants completed a range of clinical and neuropsychological assessments at each assessment. PD-MCI was classified using Movement Disorders Society (MDS) Task Force Level I (Montreal Cognitive Assessment <26) and II (using cut-offs of 1, 1.5 and 2 SD) criteria. PDD was diagnosed according to MDS criteria.

Results: 75% of participants returned for 36 month follow up (mean of 3.1±0.2 years); 8% of patients had developed PDD all of which were previously identified as PD-MCI (Level I and Level II criteria 1.5 or 2SD). Applying Level I criteria, 70% were cognitively stable, 19% cognitively declined and 11% improved over 36 months. Applying Level II criteria (1 versus 1.5 versus 2 SD) 27% were cognitively stable, 33% cognitively declined, 14% improved and 19% fluctuated over 36 months; the majority fluctuated between PD-MCI 1SD, 1.5SD and normal cognition. 18% of participants reverted to normal cognition from PD-MCI; <1% reverted at each time point when using a 2SD cut-off. PD-MCI Level I and Level II criteria (using a 2SD cut-off) classification accuracy were compared using baseline data; 53.2% (n=100) and 16.0% (n=30) were identified as normal cognition and PD-MCI, respectively, using both criteria. Data revealed 5.9% of classifications were false positive while 25.0% were false negative compared to using the more compressive Level II criteria (χ2=22.5, p<0.001).

Conclusions: Cognitive impairment in PD is complex. Some individuals’ cognitive function fluctuated over time and some reverted to normal cognition. Using level II criteria, we found more than a quarter of participants were cognitively stable over 36 months, one third cognitively declined and 14% improved. PD-MCI Level I criteria may have greater clinical convenience, but more comprehensive Level II criteria with 2SD cut-offs may offer greater diagnostic certainty.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/mild-cognitive-impairment-in-newly-diagnosed-parkinsons-disease-a-three-year-follow-up/