Background and Aims: Pain intensity as a core outcome domain is used in most clinical trials for the purpose of verifying effectiveness or efficacy of a specific treatment. For this, the Numeric Pain Rating Scale-11 (NPRS-11) is currently recommended as most appropriate [1,2]. To what extent pain intensity scales enable valid and reliable measurements in patients with chronic pain or are explicitly sensitivity to change  in interdisciplinary multimodal paintreatment (IMPT), has only been investigated for selected pain regions and therefore not comprehensively for chronic pain [3,4]. Ultimately various pain scales are applied to measure pain intensity, but results on their quality criteria referring to IMPT context are insufficient. Accordingly, aim of this study was to provide an overview of the measurement property of unidimensional- and composite pain intensity scales.
Methods: Bibliographic databases (Medline, Embase searched up to 9/2017) and a manual search were used  to identify studies on measurement properties (validity, reliability and sensitivity to change as well as interpretability and feasibility) of unidimensional pain intensity scales for adults (≥ 18 years) who suffer chronic pain (≥ 3 months). The methodological quality of all eligible studies and the adequacy of the measurement properties were assessed independently by two observers with the COSMIN-Risk-of-bias-checklist [5]. An evidence synthesis summarizing findings from different studies proposed by the COSMIN group was applied. Quality of evidence includes study quality, number of studies and sample size. 
Results: Based on the research, a total of 21 publications were included. Commonly applied scales comprises unidimensional one-item-scales: Numeric-Rating-Scale, Visual-Analog-Scale, Verbal-Rating-Scale, Pain-Thermometer as well as Composite Scales, which are combined One-Item-Scales (e.g. “pain severity subscale of the BPI”). For detailed results on  the scales see table 1 and 2.
Most frequently examined were construct validity and test-retest-validity as well as feasibility of pain intensity scales. Content validity was investigated in only one study, considering the NRS. This study shows fundamental limitations. Also only one study examined sensitivity to change regarding IMST both in relation to the NRS and VRS. Overall an doubtful to inadequate methodological quality was found for all studies.
Discussion: Based on the evidence presented, no scale for measuring pain intensity in adults with chronic pain can be recommended currently. Comparability of the scales is highly limited by the different presentation (anchors, time references, etc.). Further research activities on examination of content validity (i.e. questions of comprehensibility, completeness and relevance of the construct) of PI-Scales are desirable. Also the involvement of patients in research, e.g. in form of interviews or focus group discussions.

This review was conducted within the VAPAIN (Validation and Application of a patient relevant core outcome set to assess effectiveness of multimodal PAIN therapy) Initiative. VAPAIN is a project funded by BMBF (GrantNo.: 01GY1326). 
contact: VAPAIN@uniklinikum-dresden.de

Literature:
[1] Chiarotto A, Boers M, Deyo RA, et al. Core outcome measurement instruments for clinical trials in nonspecific low back pain. Pain 2018;159(3):481-495.
[2] Turk DC, Dworkin RH, Allen RR, et al. Core outcome domains for chronic pain clinical trials: IMMPACT recommendations. Pain 2003;106(3):337-345.
[3] Treede RD, Rief W, Barke A, et al. A classification of chronic pain for ICD-11. Pain 2015;156(6):1003-1007.
[4] IASP Terminology. Interdisciplinary treatment. IASP Task Force Taxonomy, Vol. 2018, 2018.
[5] Prinsen CAC, Mokkink LB, Bouter LM, et al. COSMIN guideline for systematic reviews of patient-reported outcome measures. Quality of life research : an international journal of quality of life aspects of treatment, care and rehabilitation 2018;27(5):1147-1157.

MEASUREMENT PROPERTIES OF PATIENT-REPORTED UNIDIMENSIONAL PAIN INTENSITY SCALES USED IN ADULTS WITH CHRONIC PAIN - A SYSTEMATIC REVIEW