The Performance Scales disability measure for multiple sclerosis: use and sensitivity to clinically important differences

Schwartz and Powell Health and Quality of Life Outcomes (2017) 15:47 DOI 10.1186/s12955-017-0614-z REVIEW Open Access The Performance Scales disability measure for multiple sclerosis: use and sensitivity to clinically important differences Carolyn E. Schwartz1,2* and Victoria E. Powell1 Abstract Background: In 1993, the Performance Scales© was created to assess multi-dimensional disability in multiple sclerosis (MS). This tool has been used in a variety of settings and study designs internationally. The present work provides an overview of the history and psychometric characteristics of the Performance Scales©, reviews its use over the past two decades, and summarizes its responsiveness to subgroup differences. Methods: A Google Scholar and Ovid search yielded 230 articles citing the Performance Scales©, of which 82 studies used the tool in empirical research. Twelve articles provided sufficient information to enable computation of effect sizes. Forest plots were used to show effect sizes for the overall summary score and by domain by patient demographics, MS disease trajectory, and treatment adherence. Results: The Performance Scales© evidenced sensitivity to clinically important differences by disease trajectory and age (for selected domains). In contrast, groups distinguished by patient adherence to disease-modifying therapies and ethnicity were relatively small. Conclusions: The Performance Scales© has been used in a large number of studies since its development, suggesting that this psychometrically sound tool is acknowledged to be a useful tool for MS clinical research. It is recommended that future work include the entire measure, so that the whole-person impact of MS can be characterized and considered in MS outcome research. Keywords: Patient-reported outcomes, Multiple sclerosis, Disability, Quality of life, Clinical trials outcomes, Rehabilitation, Epidemiological research, Performance Scales, Review, Responsiveness, Interpretation Background The use of patient-reported outcomes has become increasingly standard in multiple sclerosis (MS) clinical research and practice. While clinical exams can provide useful information about objective disability indicators (e.g., mobility difficulties), it is widely acknowledged that important aspects of treatment impact can only be addressed by asking the patient directly. For example, fatigue, numbness, and cognitive difficulties can impact an individual’s ability to engage in work and other important activities of daily living and they are * Correspondence: 1 DeltaQuest Foundation, Inc., 31 Mitchell Road, Concord, MA 01742, USA 2 Departments of Medicine and Orthopaedic Surgery, Tufts University Medical School, Boston, MA, USA not always visible to the ‘objective’ observer. In 1993, the Performance Scales© was created to assess multidimensional disability in MS. This tool has been used in a variety of settings and study designs internationally. Yet, recent reviews of MS outcome measures have neglected to mentioned or cite this measure [1, 2], despite its use in a substantial number of research studies. Its brevity, strong psychometric characteristics, and availability in many language translations render it useful in a number of clinical and research contexts. The present work provides an overview of the history and psychometric characteristics of the Performance Scales©, reviews its use over the past two decades, and summarizes its responsiveness to subgroup differences. © The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Schwartz and Powell Health and Quality of Life Outcomes (2017) 15:47 Page 2 of 8 History of the Performance Scales© The development of the Performance Scales© was motivated by the need to have patient-reported indices of disability to provide assessment alternatives to the neurologic examination. The gold standard for assessing disability in MS is the Expanded Disability Status Scale (EDSS) [3], which is scored on the basis of clinician answers to the Functional Systems Scores (FSS) and requires substantial clinician time (about 40 min). The EDSS score is driven by ambulation disability and does not reflect other, important but hidden (i.e., not visible) aspects of disability sufficiently (e.g., cognitive symptoms). Additionally, the EDSS has well-documented issues with inter-rater reliability in the minimal-to-moderate range of disability. This means that two neurologists rating the same individual may vary in their scoring by one point on the ten-point scale [4, 5]. This one-point difference is the same as the standard definition of clinically significant change used in clinical trials [6]. Furthermore, the EDSS is differentially sensitive to change, depending on the initial disability level. Accordingly, a change of 1 point on the EDSS reflects more dramatic change at higher levels of disability. This reliability problem reduces the responsiveness of the EDSS as well as the statistical power of any study that uses the EDSS as an outcome. In addition to the above psychometric concern of reliability, the Performance Scales© measure was created to consider more relevant domains of MS-specific disability. This focus on content validity was stimulated by qualitative research with MS patients in the context of developing a psychosocial intervention for patients and caregivers [7]. Elicited patient description of their disability and its impact on their life did not correspond to their healthcare providers’ descriptions of their disability [8]. The patients’ answers reflected a wide range of domains that were not reflected by the EDSS or FSS, or by generic health status measures, such as the widely used SF-36™. Hence it was clear that there was a need for a robust measure of MS disability that covered the full multi-dimensional territory affected. estimated completion time of 2 min. Higher scores represent more impairment. Psychometric characteristics of the Performance Scales© Domains The Performance Scales© includes the following eight domains: Mobility, Hand Function, Vision, Fatigue, Cognitive, Bladder/Bowel, Sensory, and Spasticity Symptoms. Validation studies of the Performance Scales© The initial validation of the Performance Scales© was a multi-site, cross sectional study implemented with 13 MS centers around the United States and Canada that was completed in 1997 [9]. The Schwartz et al. [9] study included 274 MS patients and 296 hea (...truncated)