Pain invalidation is an independent determinant of fibromyalgia, irrespective of depression.

Background: This study evaluated and compared invalidation domains (discounting and lack of understanding) in patients with fibromyalgia (FM) and non-FM chronic musculoskeletal pain. The relationship between invalidation and depression was also investigated to clarify the role of FM.

Methods: A total of 207 patients (145 FM and 62 non-FM) completed questionnaires including the Illness Invalidation Inventory (3*I), Widespread Pain Index (WPI), Revised Fibromyalgia Impact Questionnaire (FIQR), and Beck Depression Inventory-second edition (BDI-II). Adjusted linear regression analyses were performed to assess the association between the 3*I and BDI-II, and univariate and multivariate logistic regression analyses were used to examine the relationships between FM (as the dependent variable) and other variables.

Results: WPI, FIQR, BDI-II, and 3*I scores were significantly higher in FM patients than in non-FM patients. The BDI-II total score was found to be a significant predictor of discounting and lack of understanding stemming from spouse and family sources in both groups, with slightly stronger effects in the non-FM group than in FM patients. In multivariate regression analysis, discounting from family sources (odds ratio [OR] = 1.81, 95% confidence interval [CI] = 1.02-3.20, P = 0.040) and the BDI-II total score (OR = 1.12, 95% CI = 1.06-1.20, P = 0.001) remained a determinant of having FM.

Conclusions: The higher frequency of invalidation in FM patients is not fully explained by depression because of weaker statistical relationships between invalidation and depression in FM rather than other pain disorders.