Background The threshold for disease activity required to start antitumour necrosis factor (TNF) therapy has been arbitrarily set in patients with axial spondyloarthritis (axSpA) at Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) ≥4. How this relates to spinal inflammation is unknown.

Objective To systematically compare the clinical, laboratory and imaging data of patients with axSpA with respect to their BASDAI level.

Methods A total of 100 consecutive patients with axSpA who had never been treated with TNF blockers were included. Laboratory parameters, spinal MRI and x-rays were quantified. Data were stratified according to BASDAI ≥4.

Results 44 patients were diagnosed as non-radiographic axSpA (nraxSpA) and 56 patients as ankylosing spondylitis (AS): median age 40.3±10.4 years; 57% male, mean disease duration since diagnosis 6.4±8.4 years, 88% HLA-B27+, mean modified Stokes Ankylosing Spondylitis Spinal Score 8.3±16.4. 60% of patients had spinal inflammation by MRI. The stratification based on BASDAI ≥4 disclosed significant differences in most clinical parameters but not for inflammation: patients with nraxSpA and BASDAI <4 versus ≥4 had 0.9±1.4 and 0.5±0.6 inflammatory lesions/patient, respectively (p=0.6), while patients with AS had 3.6±3.7 and 2.7±3.0 inflammatory lesions/patient, respectively (p=0.4).

Conclusion The burden of inflammation is quite comparable in patients with axSpA—regardless of disease activity. These data clearly challenge the concept of the recommended cut-off point of BASDAI ≥4.