Identifying Comorbid Fibromyalgia in Inflammatory Arthritis: The Role of Disease Activity in Fibromyalgia Survey Questionnaire Performance

Objective: To evaluate the utility of the Fibromyalgia Survey Questionnaire (FSQ) as a screening tool for fibromyalgia (FM) in patients with inflammatory arthritis (IA) and to determine optimal cutoff points according to arthritis disease activity. Methods: Patients with rheumatoid arthritis (RA), axial spondyloarthritis (SpA), and psoriatic arthritis (PsA), with and without comorbid fibromyalgia (FM) at a 1:1 ratio were invited to participate in this cross-sectional study. FM status was defined by an expert physician’s diagnosis. Disease activity indexes were recorded. Participants completed the FSQ through a structured online interview. ROC analysis and the area under the curve (AUC) were calculated to identify the optimal FSQ cutoff values. Results: A total of 152 IA patients were included (72% RA, 11% SpA, and 17% PsA), 51% of whom had comorbid FM. The ability of the FSQ to differentiate comorbid FM among patients in remission or with low disease activity (n=80) was high (AUC=0.896), showing 88% sensitivity and 88% specificity at a cutoff >12. In contrast, the FSQ performance was lower in patients with moderate to very high disease activity (n=72, AUC=0.695), with 83% sensitivity and 56% specificity at a cutoff >15. Conclusions: The FSQ is a useful screening tool for identifying comorbid FM in IA patients with low disease activity or in remission, with performance comparable to the general population (cutoff value >12). Results should be interpreted cautiously in those with active disease. These findings may facilitate the recognition and management of comorbid FM in IA patients.