Validity of the modified stoke ankylosing spondylitis spine score (M-SASSS) and of the bath ankylosing spondylitis radiology index (BASRI) for the radiological assessment of axial involvement in psoriatic arthritis. multicentre validation study. Part one.

Background: The definition and measurement of axial disease in Psoriatic Arthritis (PsA) still remains problematic. So far, no instruments have been validated for the radiological assessment of axial involvement in PsA patients. There are 2 scoring methods developed for spinal assessment in AS: BASRI and m-SASSS(1-2). As there are quantitative and qualitative dissimilarities between AS and PsA axial involvement, it is not clear whether the radiographic scoring measures developed for AS will be valid for PsA as well. Objectives: To assess the validity of the 2 scores for the radiological axial involvement in PsA patients and compare their individual performance. Secondary end-points were aimed to report clinical and radiographic characteristics of the axial involvement in a group of patients with PsA. Methods: Multicentre cross-sectional study on PsA patients, regardless of the disease duration. PsA was classified on the basis of the CASPAR criteria (3). Inclusion criteria was the presence of clinical, functional and/or radiological axial involvement. Three blinded observers scored the radiographs: each radiograph was scored by using the BASRI and m-SASSS. The construct validity was assessed by examining the correlation of the scoring methods with BASFI, BASMI, RLDQ, and some anthropometric measurements. The correlation will be expressed as Spearman's rho. Results: Seventy-seven patients were enrolled (58 M, 19F, mean age 49.4±10.8, disease duration 13.95±7.91 yr). All but one satisfied CASPAR criteria. Of them 79.2% showed a peripheral joint involvement while only 20.8% were only with axial. Functional data (median, range) were: BASMI 3 (0-8), BASFI 25 (0-92), HAQ 0.75 (0-2.8),RLDQ 1 (0-3). BASDAI was 3.3 (0-9.6). BASRI and m-SASSS were (median, range): 3.25 (0-14.5) and 1 (0-60), respectively. Both measures correlated strongly with anthropometric and patient reported outcomes (see table). Cx Rotn Chest Exp Mod Schob RLDQ BASMI BASFI BASRI -0.49* -0.27 - 0.24 0.23 0.47* 0.13 mSASSS -0.41* -0.15 -0.34* 0.12 0.39* 0.10 * p < 0.01 p < 0.05. Conclusion: Both instruments are valid for measuring spinal radiological change in PsA. The BASRI is quicker and easier to perform but needs some modification to encompass the complete range of features particular to this condition. References: 1. Mackay K, Mack C, Brophy S, Calin A. The Bath Ankylosing spondylitis radiology index (BASRI). A new, validated approach to disease assessment. Arthritis Rheum 1998; 41: 2263-2270. 2. Creemers MC, Franssen MJ, van't Hof MA et al. A radiographic scoring system and identification of variables measuring structural damage in ankylosing spondylitis (thesis). Nijmegen (The Netherlands): University of Nijmegen 1994 3. Taylor W, Gladman D, Helliwell P, Marchesoni A, Mease P, Mielents H. Classification criteria for psoriatic arthritis: development of new criteria form a large international study. Arthritis Rheum 2006; 54 (8): 2665-73.