Publication: Reliability, Factor Structure and Predictive Validity of the Widespread Pain Index and Symptom Severity Scales of the 2010 American College of Rheumatology Criteria of Fibromyalgia
Authors
Galvez-Sánchez, Carmen María ; De la Coba, Pablo ; Duschek, Stefan ; Reyes del Paso, Gustavo A.
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Publisher
MDPI
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DOI
https://doi.org/10.3390/jcm9082460
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info:eu-repo/semantics/article
Description
©<2020>. This manuscript version is made available under the CC-BY license http://creativecommons.org/licenses/ccby/4.0/
This document is the Published, version of a Published Work that appeared in final form in [Journal of Clinical Medicine]. To access the final edited and published work see [https://doi.org/10.3390/jcm9082460]
Abstract
Fibromyalgia syndrome (FMS) is a chronic condition of widespread pain. In 2010, the
American College of Rheumatology (ACR) proposed new diagnostic criteria for FMS based on two
scales: the Widespread Pain Index (WPI) and Symptoms Severity (SS) scale. This study evaluated
the reliability, factor structure and predictive validity of WPI and SS. In total, 102 women with FMS
and 68 women with rheumatoid arthritis (RA) completed the WPI, SS, McGill Pain Questionnaire,
Trait Anxiety Inventory, Fatigue Severity Scale, Oviedo Quality of Sleep Questionnaire, and Beck
Depression Inventory. Pain threshold and tolerance and a measure of central sensitization to pain
were obtained by pressure algometry. Values on WPI and SS showed negative-skewed frequency
distributions in FMS patients, with most of the observations concentrated at the upper end of the
scale. Factor analysis did not reveal single-factor models for either scale; instead, the WPI was
composed of nine pain-localization factors and the SS of four factors. The Cronbach’s α (i.e., Internal
consistency) was 0.34 for the WPI,0.83 for the SS and 0.82 for the combination of WPI and SS. Scores
on both scales correlated positively with measures of clinical pain, fatigue, insomnia, depression,
and anxiety but were unrelated to pain threshold and tolerance or central pain sensitization. The
2010 ACR criteria showed 100% sensitivity and 81% specificity in the discrimination between FMS
and RA patients, where discrimination was better for WPI than SS. In conclusion, despite their
limited reliability, both scales allow for highly accurate identification and differentiation of FMS
patients. The inclusion of more painful areas in the WPI and of additional symptoms in the SS may
reduce ceiling effects and improve the discrimination between patients differing in disease severity.
In addition, the use of higher cut-off values on both scales may increase the diagnostic specificity in
Spanish samples.
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Citation
Journal of Clinical Medicine, 9(8), 2460, 2020
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