Background: Axial spondyloarthritis (axSpA) is a chronic rheumatic disease affecting mainly the axial skeleton (sacroiliitis, spondylitis). It is part of the disease spectrum spondyloarthritis, comprising a group of rheumatic diseases with a strong genetic link with HLA-B27 and an association with inflammatory back pain. AxSpA can be further divided into radiographic axial spondylitis (r-axSpA), with definite radiological signs of sacroiliitis, and non-radiographic axial spondylitis (nr-axSpA). If left untreated, axSpA can result in significant functional limitations for patients.

Assessing disease activity and treatment response in axSpA patients is challenging as various outcome measures have limitations. Radiographic damage, an objective measure, takes a long time to evaluate changes (>2 years), and inflammation markers such as CRP have moderate sensitivity and specificity. Patient-reported outcome measures, like the Bath Ankylosing Spondylitis Functional Index (BASFI), are subjective and may be influenced by psychosocial factors. Studies have found a correlation between psychosocial variables and patients’ perceived functional status, with patients experiencing lower back pain reporting higher functional disability if they have distress, anxiety, or depression.

Physical functioning is a crucial goal for axSpA patients, but for a long time, there was no physical performance test available for them. To address this gap and provide an objective measure of disease activity, treatment response, or progression, the 8-performance-based tests for axSpA were developed. However, despite being validated, they were not widely adopted in clinical practice due to their time-consuming nature. To address this, the Ankylosing Spondylitis Physical Performance Index (ASPI) was developed, which comprises of only three of the most sensitive tests from the original eight, i.e., picking up a pen from the floor, putting on socks, and standing up from the ground. One study has already shown the validity and feasibility of the ASPI, but further research is needed to confirm these findings.

Aim: This study aims to assess the validity, reliability, and feasibility of the ASPI in patients with r-axSpA and nr-axSpA in a Dutch population in clinical settings. Additionally, the study aims to determine the level of agreement between different raters in scoring the ASPI test.

Methodology: This study aims to recruit patients with axSpA from the outpatient clinic at the Amsterdam University Medical Center. The study includes three visits: one before starting treatment with a tumor necrosis factor inhibitor (TNFi), one after one week, and one after three months. The study involves two observers who will measure the patients’ performance on the three tests of the ASPI. The validity of the test will be evaluated through a patient questionnaire, where a score of 6 or higher is considered sufficient. Reliability will be assessed by calculating the intra-class coefficient, and feasibility will be evaluated by measuring the time required to complete the test, the patients’ judgement of the test’s ease of execution, and the patients’ scores on a feasibility questionnaire. The study will also examine the correlation between the ASPI and other disease activity parameters through regression analyses.

Timelines of the project: The study was initiated in 2018 and is still ongoing. A total of 45 patients were enrolled in the pilot phase of the study, and the researchers are currently in the process of recruiting an additional 10 patients with nr-axSpA who are starting their first TNFi.

Project Team

PI: Irene van der Horst – Bruinsma (Nijmegen, Netherlands)

Subinvestigator: Pasoon Hellamand (Amsterdam, Netherlands)