Background Assessing fibromyalgia (FM) is challenging due to the lack of hard outcomes and the need to rely on patient-reported symptoms. Completion of questionnaires by patients may be fraught with inaccuracy, and meaningful interpretation of results can only be performed with due consideration of the clinimetric properties and weaknesses of instruments. Global rating of change scales represent a practical method of measuring disease severity and treatment outcomes, and may be particularly useful in routine clinical practice.
Objectives To assess the validity of Patient Global Impression of Change (PGIC) in patients treated in routine clinical care.
Methods FM patients from a prospective cohort at a tertiary care multidisciplinary clinic with at least one follow-up (FUP) assessment were included. Disease severity at treatment initiation and FUP was measured with pain visual analog scale, patient global assessment (PGA), Fibromyalgia Impact Questionnaire (FIQ), Health Assessment Questionnaire (HAQ), McGill Pain Questionnaire (MPQ), and body map. PGIC was assessed at FUP. Between-group differences in disease severity improvement were assessed for statistical significance with one-way analysis of variance. Linear regression was used to assess the association between different measures. Parameter correlation was assessed with the Spearman's rank coefficient (rho).
Results 167 patients (91% female) were included with a mean (SD) age of 48.8 (9.8) years, disease duration of 10.8 (10.2) years, and FUP duration of 30.0 (15.3) months. Patients rating their condition as much/moderately/little worse vs. same vs. little/moderately/much better since treatment began experienced significant (P≤0.001) differences in change in pain (1.03 vs. 0.31 vs. -1.31), PGA (0.67 vs. 0.90 vs. -1.18), body map (2.62 vs. 1.29 vs. -3.82), FIQ (6.52 vs. -0.32 vs. -10.73), and HAQ (0.20 vs. 0.06 vs. -0.19). However, no significant differences were observed between-groups in MPQ (-0.66 vs. -1.88 vs. -6.58; P=0.086). In correlation analysis, PGIC showed a statistically significant (P<0.001) weak positive correlation with improvement in MPQ (rho=0.250), pain (rho=0.387), PGA (rho=0.327), body map score (rho=0.287), and HAQ (rho=0.343) and moderate positive correlation with FIQ improvement (rho=0.423). Regression analysis showed that a significant (P<0.01) positive association exists between improvement in all disease severity measures and PGIC. Interestingly, upon adjusting for improvement in disease activity measures, FUP duration had a significant (P<0.05) impact on PGIC with patients followed for a longer period reporting a greater improvement in their condition compared to patients followed for shorter periods.
Conclusions The results of this analysis suggest that overall, a weak correlation exists between PGIC and improvement in standard FM outcome measures. Furthermore, FUP duration was identified as a significant confounder of patient perception of disease improvement which could be due to recall bias or survival bias. Altogether, these results have important implications for FM management and designing new instruments assessing outcomes in FM.
Disclosure of Interest : M.-A. Fitzcharles Speakers bureau: Lilly, Pfizer, Purdue, Valeant, E. Rampakakis: None declared, P. Ste-Marie: None declared, J. Sampalis: None declared, Y. Shir Consultant for: McKesson Canada Corporation, Palladin Inc. Canada