Background Treatment target of patients with axial Spondyloarthritis (axSpA) is based on assessment of disease activity (remission) while the ultimate goal is improvement of Health Related Quality of Life (HRQoL). Therefore it is important to know if a change in disease activity is indeed related to a change in HRQoL.
Objectives To assess the association between the change in disease activity and change in HRQoL between baseline and one year in patients with early axSpA.
Methods The Spondyloarthritis Caught Early (SPACE) study is a prospective cohort study in patients with chronic back pain (≥3 months, ≤2 years, onset <45 years) recruited from various rheumatology centres across Europe. The 36-item Short-Form (SF-36) was completed by patients to assess HRQoL at baseline and 1 year. After recoding and recalibration, raw scale scores were converted in scale scores ranging from 0 (worst) to 100 (best). Physical (PCS) and Mental Component Summary (MCS) scores were calculated by adjusting converted scale scores for country, gender, and age, and were compared to the general population mean of 50 with a standard deviation (SD) of 10. The Ankylosing Spondylitis Disease Activity Score (CRP based; ASDAS) was calculated to assess disease activity. Linear regression models were made with change of ASDAS between baseline and 1 year (ΔASDAS) as a determinant and the change of PCS (ΔPCS) or MCS (ΔMCS) as an outcome. The models were adjusted for age. Fulfilment of the imaging or clinical arm and gender were tested for interaction.
Results A total of 86 patients fulfilled the ASAS axSpA criteria; 50 patients fulfilled the clinical arm and 36 patients the imaging arm. Mean age was 29.3 years (SD 7.7), 48.8% was male, and mean duration of back complaints was 13.8 months (SD 7.4). Patients had a mean PCS of 27.0 (SD 15.8, IQR 17.8–38.1), mean MCS of 49.3 (SD 13.0, IQR 40.0–59.4), and mean ASDAS of 2.4 (SD 1.0, IQR 1.6–3.0) at baseline. At 1 year the mean PCS increased to 36.0 (SD 13.9) and the MCS remained stable at 49.7 (SD 12.1), and mean ASDAS decreased to 2.0 (SD 0.8). As the MCS was not different from the general population, only the effect of ASDAS on PCS was determined. In the univariable model (Figure 1), a decrease of 1 unit of ASDAS between baseline and 1 year resulted in an increase of 9.7 (SE 1.5) in the PCS score over 1 year. Fulfilment of the clinical or imaging arm and gender were effect modifiers (2-way interaction) in the model for PCS (p=0.10,R2=38.6%). Results were stratified for these variables. The effect of ΔASDAS on ΔPCS was most pronounced in men (fulfilling the imaging arm (-15.8; SE 2.7) and fulfilling the clinical arm (-11.8; SE 4.0)). It was still significant but to a lesser extent in women fulfilling the clinical arm (-6.9; SE 2.1) but not in women fulfilling the imaging arm (-1.2; SE 4.8).
Conclusions Although improvement in ASDAS is correlated to improvement in the physical component of HRQoL, the impact of this correlation largely depends on gender and arm of the ASAS criteria: impact is highest in men fulfilling the imaging arm.
Disclosure of Interest None declared