Predictors of cognitive impairment in Parkinson's disease: a systematic review and meta-analysis of prospective cohort studies.

Cognitive impairment is a debilitating manifestation in Parkinson's disease (PD). We sought to investigate predictors of PD-CI (PD with cognitive impairment).We systematically searched PubMed and Cochrane Library for prospective cohort studies and pooled estimates via random-effects models. Primary analyses for all types of cognitive impairments and subgroup analyses by separate outcomes were conducted.A total of 28,009 studies were identified, of which 57 studies with 31 factors were included in the meta-analysis. In the primary analysis, 13 factors were associated with PD-CI, comprising advanced age [relative risk (RR)=1.07, 95% confidence interval (CI)=1.03-1.12], age at onset (RR=4.43, 95% CI=1.87-10.54), postural-instability-gait disorder (RR=3.76, 95% CI=1.36-10.40), higher Hoehn and Yahr stage (RR=1.83, 95% CI=1.35-2.47), higher UPDRS III score (RR=1.04, 95% CI=1.01-1.08), rapid eye movement sleep behavior disorder (RR=3.72, 95% CI=1.20-11.54), hallucinations (RR=3.09, 95% CI=1.61-5.93), orthostatic hypotension (RR=2.98, 95% CI=1.41-6.28), anxiety (RR=2.59, 95% CI=1.18-5.68), APOE 2 (RR=6.47, 95% CI=1.29-32.53), APOE 4 (RR=3.04, 95% CI=1.88-4.91), electroencephalogram theta power>median (RR=2.93, 95% CI=1.61-5.33), and alpha power

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