Disability stratification in fibromyalgia: symptom burden, centrally acting medication exposure, and functional outcomes in a multisite cohort.

PURPOSE: To determine whether disability stratification identifies clinically meaningful differences in symptom burden, centrally acting medication exposure, and health-related functioning in fibromyalgia, and to identify independent clinical correlates of physical functioning. MATERIALS AND METHODS: We analyzed a harmonized multisite cohort of 1,126 adults with physician-confirmed fibromyalgia from two U.S. academic centers. Among 976 participants with FIQR/SIQR-equivalent disability scores, high disability was defined as the upper quartile (≥65.92; n = 244). Symptom burden included CSI, BDI-II, and MPQ measures. Physical functioning was assessed using a four-domain SF-36 physical health composite. Multivariable regression identified independent correlates of physical functioning. RESULTS: High disability was associated with greater pain, central sensitization-associated symptoms, depressive symptoms, body mass index, and centrally acting medication burden, with worse functioning across all SF-36 domains (all p < 0.001). Pain showed the strongest correlation with disability (ρ = 0.72), followed by CSI (ρ = 0.59) and BDI-II (ρ = 0.48). In 875 complete cases, pain, CSI, BDI-II, body mass index, and medication burden were independently associated with worse physical functioning (adjusted R2=0.445). CONCLUSIONS: Disability stratification captures clinically meaningful fibromyalgia heterogeneity beyond pain alone and may support rehabilitation-oriented assessment and future precision rehabilitation research.