BackgroundFatigue is an important domain in quality of life of spondyloarthritis patients, not always directly associated with disease course. The explanatory factors of fatigue in these patients are still not clearly understood.ObjectivesTo assess the determinants of fatigue in patients with SpA under biologic disease modifying anti-rheumatic drugs (bDMARDs).MethodsA retrospective observational study was performed using registry data of patients with SpA under bDMARD therapy followed at a tertiary level hospital. Data regarding disease activity, response criteria measures, analytic markers, function, metrology, pain, general health and fatigue (using FACIT score) was gathered at baseline, 6 months (t6) and 12 months (t12) after introduction of bDMARD. Statistical analysis (significance at p < 0.05) was performed using paired T-test, Wilcoxon test and McNemar tests for paired samples, Mann Whitney-U, Kruskall-Walis and One Way ANOVA for independent samples. Linear and logistic regression models were performed to assess direction and strength of association.ResultsA total of 46 SpA patients were analysed; most were male (24, 52.2%) with a predominantly axial involvement (31, 68.9%) and 74.4% of them were positive for HLA-B27. Most patients had high school or lower education (29, 69.1%), never smoked (26, 61.9%), never drank (34, 79.1%) and had a full-time job (38, 88.4%). All patients were under TNF inhibitors, mostly adalimumab (23, 50%). There was a significant decrease in inflammatory markers (pAt baseline, there was a strong negative correlation between fatigue, expressed by FACIT score, and pain VAS (R = 0.9, p=0.037), without other significant associations. Several positive correlations with fatigue at t6 were observed, the strongest with anxiety and depression HADs (p < 0.001), BASFI (p < 0.001) and ASDAS-CRP (p< 0.001). Other positive associations were seen with 66 TJC (p Prediction analysis showed univariable association between several baseline variables and fatigue (lower FACIT scoring) at t6: age at bDMARD introduction (B = - 0,405, p = 0.02), age at diagnosis (B = -0.43, p = 0.02), physician VAS (B = 0.149, p < 0.05), MASES (B = -1.732, p ConclusionEnthesitis, female gender and subjective assessment of vitality seem to be determinants of fatigue in SpA patients under bDMARD. Fatigue in this population is associated with diverse factors that should be optimized in a holistic approach to the patient.Disclosure of InterestsNone declared