Background Comorbidities in rheumatoid arthritis are known to add to the burden of disease and its complexity, with implications on disease outcomes and prognosis. In Spondyloarthritis (SpA), the impact of comorbidities on outcomes is less well studied; yet, their prevalence is high.

Objectives To investigate the relationship between the comorbidity burden in SpA as measured by the Rheumatic Disease Comorbidity Index (RDCI) and: (1) disease activity; (2) function; (3) quality of life.

Methods Analysis was based on data from the ASAS COMOrbidities SPA study, ASAS-COMOSPA, a cross-sectional, multinational study involving 22 countries across four continents. Patients fulfilling the ASAS SPA criteria were included. Comorbidities were computed according to the Rheumatic Diseases Comorbidity Index (RDCI), which includes ischaemic heart disease, stroke, hypertension, lung disease (COPD), malignancy, fractures, depression, diabetes and gastrointestinal disease; range 0–9 (higher score indicating higher comorbidity burden). Univariable, followed by multivariable multilevel mixed-effects linear regression models were used to investigate the relationship between the RDCI and ASDAS(CRP), BASDAI, patient global, BASFI, and EQ5D, adjusting for clinical confounders (table). Patients were nested into their country of origin, which formed the basis of the multilevel analysis.

Results A total of 3558 patients were included in the study; 66% males, mean age 43 (SD 14), median disease duration 5 years (IQR 11) and mean RDCI 0.72 (1.08). An increase in RDCI was associated with higher BASFI, BASDAI, ASDAS and patient global score and lower EQ5D (all p<0.001) (see table). For instance a patient with an RDCI score of 2 compared to 0 had on average 0.7 point higher on the BASFI, one point higher on the BASDAI and patient global, 0.24 units higher on the ASDAS and a 0.06 points lower on the EQ-5D.

Conclusions Higher comorbidity burden is independently associated with worse outcomes in SpA as reflected by higher disease activity, worse functional and quality of life measures. The results highlight the need for promptly identifying and treating comorbidities in SpA. As with emerging evidence in RA suggesting failure to achieve treat-to-target principles in the presence of comorbidities, it is possible that comorbidities also hinder the achievement of therapeutic goals in SpA.

Disclosure of Interest None declared