Do the Activity Indices Used in Axial Spondyloarthritis Capture the Relationships Between Obesity, Smoking and Disease Activity in the Same Way?

Obesity and smoking have been related to increased disease activity in axial spondyloarthritis (axSpA), but these associations might vary depending on the composite index chosen to assess disease activity. We aimed to check this possibility. Three hundred and thirty consecutive patients were recruited from the monographic axSpA unit of a university center. To assess disease activity, BASDAI and ASDAS-CRP measurements were collected. The factors associated with the different disease activity thresholds of these instruments were analyzed using univariate and multivariate logistic regression models. This study included 127 women and 203 men, with a mean age of 47.6 (SD 12.9) years, median disease duration of 8 years [IQR: 4-16], and 63% on biologic therapies. Most patients met the therapeutic goals, with a BASDAI < 4 in 187 (56.7%) and ASDAS inactive/low category in 182 (55.2%). Being male was associated with BASDAI remission (OR 2.63), but smoking reduced this likelihood (OR 0.28). Similar findings were found for ASDAS inactive disease (male: OR 2.09; smoking: OR 0.39). The variables associated with BASDAI ≥ 4 in the multivariate logistic model were the male gender (OR 0.36), age (OR 1.02), smoking (OR 2.39), and obesity (OR 2.94), whereas those associated with active/very active ASDAS categories were the male gender (OR 0.49), age (OR 1.02), and smoking (OR 2.34). However, obesity was not associated with these higher ASDAS categories ( = 0.183). While the association between smoking and increased disease activity was consistent across all composite activity indices, the obesity-activity relationship was only apparent through the BASDAI.