How to define remission in ankylosing spondylitis?

The new term axial spondyloarthritis (SpA) covers both patients with ankylosing spondylitis (AS) according to the modified New York criteria, for which the presence of radiographic sacroiliitis is mandatory, and patients with non-radiographic axial disease. The latter group can be defined either by the presence of active inflammatory sacroiliitis on MRI or by the presence of clinical parameters in addition to a positive human leucocyte antigen-B27 testing. This classification according to the new ‘Assessment in SpondyloArthritis international Society’ (ASAS) criteria1 allows an earlier diagnosis of these patients before chronic changes visible by x-ray examination have already occurred. The question of remission should therefore be discussed for the whole group of patients with axial SpA, especially because remission might be reached more easily if patients are treated earlier. Remission can be divided into (1) clinical remission; (2) absence of objective inflammation such as a raised C-reactive protein (CRP) or active inflammation on MRI shown on a short τ inversion recovery (STIR) sequence; (3) reaching normal function; (4) prevention of (further) structural damage and (5) remission of extra-articular manifestations/associated diseases such as uveitis, psoriasis or inflammatory bowel disease (IBD). Several clinical scores are available for the measurement of clinical activity. The ‘Bath Ankylosing Spondylitis Disease Activity Index’ (BASDAI)2 grades fatigue, back pain, swelling/pain of peripheral joints and morning stiffness on a mean scale between 0 and 10 (or between 0 and 100). Although the BASDAI is widely used in clinical practice, no remission criteria have been defined for this index. However, the ASAS group defined clinical remission criteria in 2001 using the domains patient global, patient pain, function (applying the Bath Ankylosing Spondylitis Functional Index, BASFI) and inflammation (using the two morning stiffness questions from the BASDAI). Clinical remission is reached when the score for each of the four domains …