Baseline Results from Proof – A 5-Year Observational Study of Long-Term Disease Outcome in Axial Spondyloarthritis

Abstract

Background Axial spondyloarthritis (axSpA), encompassing ankylosing spondylitis (AS) and non-radiographic axSpA (nr-axSpA) without advanced structural lesions in the sacroiliac joints (SIJ), is a relatively new disease concept. The natural disease course of axSpA, including progression of structural damage over time, has not yet been systematically studied in large patient (pt) groups.

Objectives To report the baseline data of PROOF, a large study currently being conducted in 29 countries across the world, evaluating long-term outcomes in pts with axSpA classified by ASAS criteria.

Methods PROOF is a multi-country prospective observational study evaluating axSpA pts in rheumatology clinical practice over 5 years. Pts with axSpA fulfilling ASAS classification criteria were eligible, if diagnosed ≤12 months prior to study enrolment. Investigator's confidence with the diagnosis of axSpA is ascertained on a numeric rating scale (NRS 0–10) at enrolment and end of follow-up. Assessments of disease activity (BASDAI, ASDAS-CRP), physical function (BASFI), quality of life (SF-12v2), productivity (WPAI-SHP), and pelvic X-ray are scheduled at yearly follow-up visits. X-rays are graded according to NY criteria by local and central readers.

Results 2084 pts with axSpA fulfilling ASAS criteria have been enrolled in PROOF study, 1259 pts with AS (60%) and 825 pts with nr-axSpA (40%) according to the investigators. The level of confidence with the diagnosis of axSpA was 8.7±1.8. The imaging criterion was fulfilled by 85% of pts (40% MRI, 51% X-ray, 9% both), 15% of pts were classified through the clinical arm. HLA-B27 was tested in 85% of pts and found to be positive in 68% of cases (70% with AS and 60% with nr-axSpA). Overall, pts were in their mid-thirties, had a long delay in referral to rheumatologist and recently diagnosed axSpA. Comparison of demographic and clinical characteristics between pts with AS and nr-axSpA is shown in Table 1. Pelvic x-rays were reportedly done in 1635 (78%) pts within 6 months of the baseline visit; to date both local and central readers have scored x-rays of 1344 pts (82% of available). Of the 1344 pts, 83.3% retained their classification (AS or nr-axSpA) after the central reading, while 16.7% were classified differently. Based on the kappa value, there was a substantial agreement on the grading of x-rays between the local and central readers: kappa=0.63 (95% CI, 0.59–0.68).