Functional (Psychogenic) Symptoms in Parkinson’s Disease Isabel Pare es, MD, 1† Tabish A. Saifee, MRCP, 1† Maja Kojovic, MD, 1,2 Panagiotis Kassavetis, MD, 1 Ignacio Rubio-Agusti, MD, 1,3 Anna Sadnicka, MRCP, 1 Kailash P. Bhatia, MD, FRCP, 1 and Mark J. Edwards, MD, PhD 1 * 1 Sobell Department of Motor Neuroscience and Movement Disorders, University College London (UCL) Institute of Neurology, Queen Square, London, United Kingdom 2 Department of Neurology, University of Ljubljana, Ljubljana, Slovenia 3 Movement Disorders Unit, Neurology Department, Hospital Universitari La Fe, Valencia, Spain ABSTRACT: It has been reported that patients who have Parkinson’s disease have a high prevalence of somatisation (functional neurological symptoms) compared with patients who have other neurodegenerative conditions. Numerous explanations have been advanced for this phe- nomenon. Here, with illustrative cases, we discuss this topic, including its clinical importance, and suggest a link between the pathophysiology of Parkinson’s disease and the proposed propensity to develop functional symptoms. V C 2013 International Parkinson and Movement Disorder Society Key Words: Parkinson’s disease; functional overlay; attention; goal-directed motor control The Problem Patients who are diagnosed with a neurological dis- ease may have additional symptoms that are consid- ered to be unexplained by that disease and, instead, are best characterised as functional (psychogenic) symptoms. This phenomenon, also called “functional overlay,” appears to be very common within neuro- logical practice. 1 A recent study has estimated that 12% of patients who are diagnosed with a neurological disease in a general neurology outpatient clinic also display “symptoms unexplained by the dis- ease” with a similar frequency across all neurological disease categories. 1 There were no clear differences found in rates of functional symptoms among different categories of neurological disorders; however, the cate- gorisation of disease diagnoses used in that study was broad (eg neuromuscular disorders vs dementia) and might have missed differences in prevalence of overlay between narrower disease categories. Of particular relevance to movement disorders specialists, one group has observed that somatoform disorders are more common in patients with Parkinson’s disease (PD) and dementia with Lewy bodies than in patients with Alz- heimer’s disease or other atypical parkinsonisms. 2,3 Among the functional disorders described in those studies, motor symptoms were common, including bent knee, tiptoeing gait, stiff leg hemiparetic gait, pa- resis with Hoover’s sign, or functional bradykinesia. The Theories Why might patients with PD be particularly suscep- tible to developing functional symptoms as proposed? Several theories have been advanced. It is acknowl- edged that PD is associated with psychiatric disorders, including depression and impulse control disorders. 3 It has been suggested that functional symptoms could be part of the psychiatric spectrum of PD. 3 PD may be accompanied by delusions; and, although somatic ------------------------------------------------------------ Additional Supporting Information may be found in the online version of this article. *Correspondence to: Dr. Mark J. Edwards, Sobell Department of Motor Neuroscience and Movement Disorders, UCL Institute of Neurology, Queen Square, London, WC1N 3BG. United Kingdom; m.j.edwards@ucl.ac.uk Isabel Par es and Tabish A. Saifee contributed equally to this article. Relevant conflicts of interest/financial disclosures: Nothing to report. Full financial disclosures and author roles may be found in the online ver- sion of this article. Funding agencies: Mark J. Edwards is funded by the National Institute for Health Research (NIHR) (6187). Isabel Pare es is funded by a Funda- cion Alfonso Martin Escudero Grant. Tabish A. Saifee is funded by the NIHR. Anna Sadnicka is funded by the Guarantors of Brain with an Asso- ciation of British Neurologists Clinical Training. This work was undertaken at UCL Hospital/UCL, which received a proportion of funding from the Department of Health s National Institute for Health Research Biomedical Research Centre funding scheme. Received: 22 October 2012; Revised: 30 April 2013; Accepted: 2 May 2013 Published online 4 June 2013 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/mds.25544 VIEWPOINT 1622 Movement Disorders, Vol. 28, No. 12, 2013