To clarify sex differences in early axial spondyloarthritis (SpA).
In total, 475 patients included in the Devenir des Spondylarthropathies Indifférenciées Récentes (Outcome of Recent Undifferentiated Spondylarthropathies) cohort, a prospective multicenter French cohort of patients with early inflammatory back pain suggestive of SpA, and fulfilling the Assessment of SpondyloArthritis international Society (ASAS) classification criteria for axial SpA were studied. The clinical and imaging features were compared between sexes and according to the clinical or imaging arm of the ASAS criteria using univariate and multivariate analysis.
Comparisons between the 239 men and 236 women showed that women had higher disease activity when measured by the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and Bath Ankylosing Spondylitis Patient Global Score and higher fatigue and functional scores despite having less radiographic sacroiliitis and magnetic resonance imaging (MRI) inflammation of sacroiliac joints and the spine than men. Disease activity measured by the C-reactive protein (CRP)-based Ankylosing Spondylitis Disease Activity Score was not different between men and women. In contrast to patients classified with the clinical arm, disease activity and functional scores did not differ between women and men with sacroiliitis on imaging scans, except for fatigue and the Ankylosing Spondylitis Quality of Life questionnaire. Women with sacroiliitis had more peripheral involvement and more family history, whereas HLA-B27 positivity, elevated CRP, and MRI inflammation of the spine were associated with male sex.
Women with early axial SpA according to the ASAS criteria had greater disease activity when measured by the BASDAI and worse functioning despite fewer radiologic abnormalities than men. The differences in disease expression may be confounding factors to establish the diagnosis of SpA and to assess disease activity in women, suggesting that the imaging arm is a pivotal measure in the ASAS criteria.