A meta‐analysis of neurocognition in mild cognitive impairment in Parkinson’s disease and progression to Parkinson’s disease dementia

Background Parkinson’s disease (PD) is a neurodegenerative condition resulting in characteristic motor impairments and cognitive changes, including executive functioning (EF) deficits. These cognitive changes worsen for the approximately 30% who develop Parkinson’s disease dementia (PDD). Mild cognitive impairment (MCI) is a transitional state between normal cognition and dementia. Although PD‐MCI and its neurocognitive correlates have been increasingly studied as an indicator of risk for PDD, the typical PD‐MCI neurocognitive profile remains undefined. The present meta‐analysis examined cross‐sectional studies administering neuropsychological testing to PD‐MCI and cognitively normal PD to provide aggregated effect sizes of group test performance by neurocognitive domain. Longitudinal studies examining PD‐MCI to PDD progression were subsequently meta‐analyzed. Method Data were coded from 92 cross‐sectional papers for PD‐MCI vs. cognitively normal PD groups. Data were coded from five longitudinal papers for PD‐MCI converting to PDD vs. PD‐MCI not converting to PDD. Random effects meta‐analytic models were conducted to provide aggregated weighted effect sizes (Hedges’ g ), indicating the difference between these groups in their respective analyses. Result Cross‐sectional results indicate that overall cognitive measures produced a large effect size ( g = 1.07, 95% CI [0.99, 1.14], p < .05) with tests of visual delayed memory producing the largest effect size ( g = 1.90, 95% CI [1.03, 2.77], p < .05). Longitudinal results indicate that overall cognitive measures produced a medium effect size ( g = 0.48, 95% CI [0.41, 0.55], p < .05) with tests of executive functioning producing the largest effect size ( g = 0.70, 95% CI [0.51, 0.89], p < .05). Conclusion Results of the first PD‐MCI meta‐analysis indicate that, across cross‐sectional and longitudinal studies, measures of cognitive performance have value in differentiating PD‐MCI from cognitively normal PD and PD‐MCI and PDD. Within cross‐sectional studies, tests of visual delayed memory produced the largest effect size, with group performance differing by approximately two standard deviations. This result may further reflect EF deficits common in PD, as well as a temporally mediated process classically more characteristic of other dementia syndromes. Longitudinal results further highlight the importance of EF changes in progressing PD and suggest power to predict progression to PDD.