title: Meta-analysis of risk factors for Parkinson's disease dementia.
abstract: BACKGROUND
  Parkinson's disease (PD) is a common heterogeneous neurodegenerative disorder in elder population. Parkinson's disease dementia (PDD) is one of the most common non-motor manifestations in PD patients. No comprehensive review has been conducted to assess risk factors for PDD.
  
  
  METHODS
  A systemic search for studies on PDD risk factors was performed. Cohort and case-control studies that clearly defined PDD and presented relevant data were included. The data were analyzed to generate a pooled effect size and 95 % confidence interval (CI). Publication bias was assessed using the Egger's test and the Begg's test.
  
  
  RESULTS
  A systematic search was conducted and yielded 5195 articles. After screening, 25 studies were included in the current analysis. Development of PDD was positively associated with age (odds ratio [OR] 1.07, 95 % CI 1.03-1.13), male (OR 1.33, 95 % CI 1.08-1.64), higher Unified Parkinson's Disease Rating Scale (UPDRS) part III scores (relative risk [RR] 1.04, 95 % CI 1.01-1.07), hallucination (OR 2.47, 95 % CI 1.36-4.47), REM sleep behavior disorder (RBD) (OR 8.38, 95 % CI 3.87-18.08), smoking (ever vs. never) (RR 1.93, 95 % CI 1.15-3.26) and hypertension (OR 1.57, 95 % CI 1.11-2.22). An inverse association was found between education (RR 0.94, 95 % CI 0.91-0.98) and PDD. Other reported factors, including age of onset, disease duration of PD, Hoehn and Yahr stage and diabetes mellitus were not significantly associated with PDD.
  
  
  CONCLUSIONS
  Advanced age, male, higher UPDRS III scores, hallucination, RBD, smoking and hypertension increase the risk of PDD, whereas higher education is a protective factor for PDD.
authors.affiliation: Department of Neurology, West China Hospital, Sichuan University, 610041 Chengdu, Sichuan China.
authors.forename: Yaqian
authors.initials: Y
authors.lastname: Xu
authors.affiliation: Department of Neurology, West China Hospital, Sichuan University, 610041 Chengdu, Sichuan China.
authors.forename: Jing
authors.initials: J
authors.lastname: Yang
authors.affiliation: Department of Neurology, West China Hospital, Sichuan University, 610041 Chengdu, Sichuan China.
authors.forename: Huifang
authors.initials: H
authors.lastname: Shang
keywords: Dementia; Parkinson’s disease; Predictors; Risk factors