title: Evaluating Disease Severity in Chronic Pain Patients with and without Fibromyalgia: A Comparison of the Symptom Impact Questionnaire and the Polysymptomatic Distress Scale.
abstract: OBJECTIVE
  To compare the relative effectiveness of the Polysymptomatic Distress Scale (PSD) with the Symptom Impact Questionnaire (SIQR), the disease-neutral revision of the updated Fibromyalgia Impact Questionnaire (FIQR), in their ability to assess disease activity in patients with rheumatic disorders both with and without fibromyalgia (FM).
  
  
  METHODS
  The study included 321 patients from 8 clinical practices with some 16 different chronic pain disorders. Disease severity was assessed by the Medical Outcomes Study Short Form-36 (SF-36). Univariate analyses were used to assess the magnitude of PSD and SIQR correlations with SF-36 subscales. Hierarchical stepwise regression was used to evaluate the unique contribution of the PSD and SIQR to the SF-36. Random forest regression probed the relative importance of the SIQR and PSD components as predictors of SF-36.
  
  
  RESULTS
  The correlations with the SF-36 subscales were significantly higher for the SIQR (0.48 to 0.78) than the PSD (0.29 to 0.56; p < 0.001). Stepwise regression revealed that the SIQR was contributing additional unique variance on SF-36 subscales, which was not the case for the PSD. Random forest regression showed SIQR Function, Symptoms, and Global Impact subscales were more important predictors of SF-36 than the PSD. The single SIQR pain item contributed 55% of SF-36 pain variance compared to 23% with the 19-point WPI (the Widespread Pain Index component of PSD).
  
  
  CONCLUSIONS
  The SIQR, the disease-neutral revision of the updated FIQ, has several important advantages over the PSD in the evaluation of disease severity in chronic pain disorders.
authors.affiliation: From the State University of New York (SUNY) at Stony Brook, Stony Brook, New York; Oregon Health and Science University, Portland, Oregon, USA.R. Friend, PhD, Professor of Psychology, Stony Brook University, and Adjunct Professor of Nursing, Oregon Health and Science University; R.M. Bennett, MD, Professor of Medicine and Nursing, Oregon Health and Science University. ronald.friend@stonybrook.edu.
authors.forename: Ronald
authors.initials: R
authors.lastname: Friend
authors.affiliation: From the State University of New York (SUNY) at Stony Brook, Stony Brook, New York; Oregon Health and Science University, Portland, Oregon, USA.R. Friend, PhD, Professor of Psychology, Stony Brook University, and Adjunct Professor of Nursing, Oregon Health and Science University; R.M. Bennett, MD, Professor of Medicine and Nursing, Oregon Health and Science University.
authors.forename: Robert M
authors.initials: RM
authors.lastname: Bennett
mesh_terms: D000328:Adult; D000367:Age Factors; D000704:Analysis of Variance; D059350:Chronic Pain / Q000175:diagnosis* / Q000523:psychology / Q000628:therapy; D015331:Cohort Studies; D003863:Depression / Q000175:diagnosis* / Q000453:epidemiology; D005260:Female; D005356:Fibromyalgia / Q000175:diagnosis* / Q000523:psychology* / Q000628:therapy; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D010147:Pain Measurement; D011788:Quality of Life; D012044:Regression Analysis; D015203:Reproducibility of Results; D018570:Risk Assessment; D012720:Severity of Illness Index; D012737:Sex Factors; D018434:Sickness Impact Profile; D013315:Stress, Psychological; D011795:Surveys and Questionnaires; D055815:Young Adult
keywords: FIBROMYALGIA; FIBROMYALGIA IMPACT QUESTIONNAIRE; MEDICAL OUTCOMES STUDY SHORT FORM-36; POLYSYMPTOMATIC DISTRESS; POLYSYMPTOMATIC DISTRESS SCALE; SYMPTOM IMPACT QUESTIONNAIRE