Development and validation of the deep brain stimulation impairment scale (DBS-IS) Franziska Maier a, *, 1 , Catharine J. Lewis a, 1 , Carsten Eggers a , Andrea A. Kühn b , Henriette Krug b , Jens Volkmann c , Anna D. Kirsch c , Lars Wojtecki d , Alfons Schnitzler d , Günther Deuschl e , Joachim K. Krauss f , Christiane Woopen g , Lars Timmermann a a Department of Neurology, University of Cologne, Cologne, Germany b Department of Neurology, Movement Disorders Unit, Charit e d University Medicine (CVK), Berlin, Germany c Department of Neurology, University of Wuerzburg, Wuerzburg, Germany d Department of Neurology, Movement Disorders and Neuromodulation, University Clinic Duesseldorf, Duesseldorf, Germany e Department of Neurology, Christian-Albrecht-University, Kiel, Germany f Department of Neurosurgery, Medical School Hannover, Hannover, Germany g Research Unit Ethics, Institute for the History of Medicine and Medical Ethics, University of Cologne, Cologne, Germany article info Article history: Received 1 July 2016 Received in revised form 5 December 2016 Accepted 5 January 2017 Keywords: Parkinson's disease Deep brain stimulation Quality of life Patient outcome Factor analysis abstract Background: Bilateral deep brain stimulation of the subthalamic nucleus (STN-DBS) has considerable influence on motor and non-motor symptoms in Parkinson's disease (PD). While improvements in motor functioning can be easily assessed with general quality of life questionnaires, the measurement of spe- cific STN-DBS-associated impairments often remains insufficient. Hence, we aimed to develop a ques- tionnaire that measures STN-DBS-related impairments. Methods: The development of the (STN-)DBS Impairment Scale (DBS-IS) consisted of four steps. First, 30 semi-structured interviews before, three and twelve months after STN-DBS-surgery were performed to create 76 items that relate to motor and non-motor functioning in STN-DBS PD patients. Second, pilot- testing led to a rewording of the questions for better understanding. Third, a first multicentre survey was performed to reduce items by applying principal component analysis (PCA). Fourth, a second multicentre survey was conducted to examine factor structure, reliability (internal consistency) and validity. Results: After the first survey (N ¼ 215), the PCA lead to a reduction of 54 items. After the second survey (N ¼ 391), exploratory factor analysis determined six factors with 22 items: 1. Postural instability and gait difficulties (5 items), 2. Cognitive impairment (5 items), 3. Speaking problems (3 items), 4. Apathy (3 items), 5. Impulsivity (3 items), and 6. Difficulties related to the DBS device (3 items). High reliability was reported for all subscales (Cronbach's alpha 0.71e0.90). Similarly, construct validity was high (r > 0.50, p < 0.001). Conclusions: With this new questionnaire patients can be followed-up and STN-DBS-specific problems might be adequately measured. Also, comparisons between patients with and without STN-DBS might be possible. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction The improvement of quality of life (QoL) by bilateral deep brain stimulation (DBS) of the subthalamic nucleus (STN) in patients with Parkinson's disease (PD) is widely established [1,2]. In large ran- domized controlled multicentre studies the advantage of QoL improvement compared to best medical treatment was repeatedly demonstrated [1,2]. In the past years it has been shown that this general QoL-improvement mostly relies on the reduction of motor impairment and therefore physical dimensions of QoL showed improvements, while non-motor symptoms might have been un- affected and prevailed [3,4]. The Parkinson's disease questionnaire-39 (PDQ-39; [5,6]) is the * Corresponding author. Department of Neurology, University Hospital Cologne, Kerpener Str. 62, D-50937 Cologne, Germany. E-mail address: franziska.maier@uk-koeln.de (F. Maier). 1 Authors contributed equally to this work. Contents lists available at ScienceDirect Parkinsonism and Related Disorders journal homepage: www.elsevier.com/locate/parkreldis http://dx.doi.org/10.1016/j.parkreldis.2017.01.002 1353-8020/© 2017 Elsevier Ltd. All rights reserved. Parkinsonism and Related Disorders xxx (2017) 1e7 Please cite this article in press as: F. Maier, et al., Development and validation of the deep brain stimulation impairment scale (DBS-IS), Parkinsonism and Related Disorders (2017), http://dx.doi.org/10.1016/j.parkreldis.2017.01.002