Validity of the Central Sensitization Inventory compared with traditional measures of disease severity in fibromyalgia

Objective: The goal of the present study was to explore additional evidence of convergent and discriminant validity of the Central Sensitization Inventory (CSI) in a large sample of subjects with fibromyalgia (FM). Methods: Patients were consecutively enrolled for a cross-sectional assessment comprehensive of three FM-specific measures (the revised Fibromyalgia Impact Questionnaire [FIQR], the modified Fibromyalgia Assessment Status [modFAS], and the Polysymptomatic Distress Scale [PDS]) and of CSI. To test the convergent validity, the Spearman's rho was used to measure the degree of correlation between the variables CSI and the FM-specific measures. To assess discriminant validity, CSI scores were grouped according to FIQR disease severity states, and differences between these groups studied with the Kruskal-Wallis test. Interpretative cut-offs were established with the interquartile reconciliation approach. Results: The study included 562 FM patients, 199 (35.4%) were classified as having central sensitization syndrome (CSI ≥40). CSI was largely correlated with modFAS (rho = 0.580; p <0.0001), FIQR (rho = 0.542; p <0.0001), and PDS (rho = 0.518; p <0.0001). The differences between the CSI scores in accordance with the FIQR were significant (p <0.000001). CSI cut-offs proposed for FM: 21 between remission and mild severity, 30 between mild and moderate severity, 37 between moderate and severe disease, and 51 between severe and very severe disease. Conclusion: The current study successfully showed additional evidence of the convergent and discriminant validity of the CSI in FM patients.