Comorbid fibromyalgia impairs the effectiveness of biologic drugs in patients with psoriatic arthritis

Objectives. To evaluate the impact of FM on the clinical outcomes of biologics in patients with PsA in real life. Methods. FM was diagnosed according to current criteria among PsA patients starting a first biologic drug from 2010 through 2017. At each visit, disease activity of PsA (DAPSA), minimal disease activity (MDA), HAQ, rate of patients achieving DAPSA-based low disease activity (LDA) or remission, and MDA were evaluated. Lost patients or those not achieving the target were imputed as non-responders. The drug survival was evaluated by Kaplan-Meyer analysis. Estimated hazard ratios (HRs) of discontinuing therapy or achieving MDA were assessed by multivariate regression models. Results. A total of 238 patients, of whom 58 had also FM, started a first biologic drug. Compared with no-FM PsA, FM PsA patients were more frequently female (P = 0.0001) with polyarticular subset (P = 0.0001), and with higher mean BMI (P = 0.006). Drug survival was significantly lower in FM PsA (50%, mean 32 months) than in no-FM PsA (74%, mean 42 months, P = 0.0001). Rates of remission/LDA and MDA were significantly lower in FM PsA at 3, 6, 12 and 24 months (P < 0.001). Remission in FM PsA was negligible (3.4% and 0% at 3 and 6 months, respectively). Negative predictors of drug discontinuation were no FM (HR 0.51) and normal weight (HR 0.29), while no FM (HR 2.54) and male sex (HR 1.58) were positive predictors of long-standing MDA. Conclusions. Comorbid FM, along with female gender and obesity seem to be the worst combination of negative prognostic factors in PsA.