Stability of mild cognitive impairment in newly diagnosed Parkinson's disease

Abstract

Background: Mild cognitive impairment (MCI) is common in early Parkinson's disease (PD). We evaluated the stability of PD-MCI over time to determine its clinical utility as a marker of disease.

Methods: 212 newly diagnosed participants with PD were recruited into a longitudinal study and reassessed after 18 and 36 months. Participants completed a range of clinical and neuropsychological assessments. PD-MCI was classified using Movement Disorders Society Task Force level I (Montreal Cognitive Assessment <26) and level II (using cut-offs of 1, 1.5 and 2SD) criteria.

Results: After 36 months, 75% of participants returned; 8% of patients had developed a dementia all of which were previously PD-MCI. Applying level I criteria, 70% were cognitively stable, 19% cognitively declined and 11% improved over 36 months. Applying level II criteria (1, 1.5 and 2SD), 25% were cognitively stable, 41% cognitively declined, 15% improved and 19% fluctuated over 36 months. 18% of participants reverted to normal cognition from PD-MCI.

Discussion: Cognitive impairment in PD is complex, with some individuals' function fluctuating over time and some reverting to normal cognition. 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.

Keywords: COGNITION; DEMENTIA; PARKINSON'S DISEASE.

Figure 1

Changes in cognitive classification from baseline to 36 months. (A) Change in cognitive classification using MDS PD-MCI level II criteria to classify PD-MCI using cut-offs of 1, 1.5 and 2SD. (B) Change in cognitive classification using MDS PD-MCI level I criteria to classify PD-MCI using MoCA score. Twenty-three participants did not complete MoCA at baseline and were excluded from this analysis. Percentages relate to the proportion of participants evaluated at that time point: baseline, 18 or 36 months. MDS, Movement Disorders Society; MoCA, Montreal Cognitive Assessment; PD-CN, Parkinson's disease with normal cognition; PD-MCI, mild cognitive impairment in Parkinson's disease; PDD, Parkinson's disease dementia.