A Systematic Review of Prevalence Studies of Depression in Parkinson’s Disease Jennifer S.A.M. Reijnders, MA, 1 Uwe Ehrt, MD, 2 Wim E.J. Weber, MD, PhD, 3 Dag Aarsland, MD, PhD, 2,4 and Albert F.G. Leentjens, MD, PhD 1 * 1 Department of Psychiatry, Maastricht University Hospital, Maastricht, The Netherlands 2 Section of Geriatric Psychiatry, Stavanger University Hospital, Stavanger, Norway 3 Department of Neurology, Maastricht University Hospital, Maastricht, The Netherlands 4 School of Medicine, University of Bergen, Bergen, Norway Abstract: Prevalence rates of depressive disorders in Parkin- son’s disease (PD) vary widely across studies, ranging from 2.7% to more than 90%. The aim of this systematic review was to calculate average prevalences of depressive disorders taking into account the different settings and different diagnostic approaches of studies. Using Medline on Pubmed, a systematic literature search was carried out for studies of depression in Parkinson’s disease. A total of 104 articles were included and assessed for quality; 51 articles fulfilled the quality criteria. Multiple publications from the same database were not in- cluded in the meta-analysis. In the remaining 36 articles, the weighted prevalence of major depressive disorder was 17% of PD patients, that of minor depression 22% and dysthymia 13%. Clinically significant depressive symptoms, irrespective of the presence of a DSM defined depressive disorder, were present in 35%. In studies using a (semi) structured interview to establish DSM criteria, the reported prevalence of major depressive disorder was 19%, while in studies using DSM criteria without a structured interview, the reported prevalence of major depres- sive disorder was 7%. Population studies report lower preva- lence rates for both major depressive disorder and the clinically significant depressive symptoms than studies in other settings. This systematic review suggests that the average prevalence of major depressive disorder in PD is substantial, but lower than generally assumed. © 2007 Movement Disorder Society Key words: Parkinson’s disease; depressive disorder; dys- thymia; prevalence; systematic review. INTRODUCTION Parkinson’s disease (PD) is a neurodegenerative dis- order characterized by tremor, bradykinesia, rigidity, and postural instability. In addition, a high prevalence of psychopathological syndromes is reported, including af- fective disorders, cognitive deterioration, and perceptual and behavioral symptoms. Depression is known to have a major impact on the prognosis of PD: depressed PD patients score lower on scales assessing motor function and activities of daily living (ADL), exhibit more cog- nitive symptoms, and report a lower quality of life. 1–3 Despite this, depression in PD is underdiagnosed and under-treated. 4,5 Prevalence rates of depressive syndromes in PD that are reported in the literature vary widely, ranging from 2.7% to more than 90%. 6–8 Possible reasons for this variation in- clude the nature of the population studied, the way the diagnosis is established, the types of depressive disorder included in the study, and the statistical measures used. In studies assessing the presence of depressive disorders in patients with physical comorbidity in general, the lowest prevalences are reported in population studies, whereas studies in outpatient and inpatient settings tend to report higher prevalence rates. Studies measuring depressive symptoms on a rating scale may yield higher prevalences This article is part of the journal’s CME program. The CME form can be found on page 313 and is available online at http://www.move- mentdisorders.org/education/activities.html This article contains supplementary material available via the Inter- net at http://www.interscience.wiley.com/jpages/0885–3185/suppmat. *Correspondence to: A.F.G. Leentjens, Department of Psychiatry, Maastricht University Hospital, P.O. Box 5800, 6202 AZ Maastricht, The Netherlands. E-mail: a.leentjens@np.unimaas.nl Received 3 May 2007; Revised 2 August 2007; Accepted 2 October 2007 Published online 6 November 2007 in Wiley InterScience (www. interscience.wiley.com). DOI: 10.1002/mds.21803 Movement Disorders Vol. 23, No. 2, 2008, pp. 183–189 © 2007 Movement Disorder Society CME 183