J Neurol Neurosurg Psychiatry 84:1265-1272 doi:10.1136/jnnp-2013-305021
  • Movement disorders
  • Review

The heterogeneity of cognitive symptoms in Parkinson's disease: a meta-analysis

  1. Laura Monetta1,2
  1. 1Department of Rehabilitation, Faculty of Medicine, Laval University, Quebec, Canada
  2. 2Department of clinical and cognitive neuroscience, Institut Universitaire en santé mentale de Québec, Quebec, Canada
  3. 3Department of Psychiatry and Neuroscience, Faculty of Medicine, Laval University, Quebec, Canada
  1. Correspondence to Dr Laura Monetta, Department of clinical and cognitive neuroscience, Institut universitaire en santé mentale de Québec (IUSMQ), 2601, rue de la Canardière, Quebec, Canada G1J 2G3; laura.monetta{at}
  • Received 23 January 2013
  • Revised 19 March 2013
  • Accepted 20 March 2013
  • Published Online First 20 April 2013


Several studies have reported heterogeneity in cognitive symptoms associated with specific characteristics of patients with Parkinson's disease (PD). Indeed, researchers have characterised subtypes of patients suffering from PD according to various criteria. Those most frequently used are the type of predominant motor symptoms (tremors or non-tremor symptoms), age at onset and presence of depression. Some characteristics, like the predominant motor subtypes, as well as the presence of depression, are more widely used to categorise cognitive differences between patients. The goal of this study was to analyse the impact of the type of predominant motor symptoms and depression on cognition in PD. A meta-analysis of 27 studies (from 1989 to 2012) was carried out to calculate the average effect size of these factors on the most often used cognitive test during those past years to evaluate cognitive skills, the Mini-Mental State Examination. The studies analysed showed significant mean weighted effect sizes on cognition for the type of motor symptoms (d=0.42; 95% CI 0.30 to 0.54) and for depression (d=0.52; 95% CI 0.38 to 0.66). These results suggested that PD participants with non-tremor predominant motor symptoms or with depression had more or more severe cognitive impairments. Identification of different subtypes in PD is important for a better understanding of the cognitive symptoms associated with this disease. Better knowing the impact of different features of PD subgroups could help to design more appropriate treatments for patients with PD.

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