Abstract
BACKGROUND: Spondyloarthritis is divided into axial and peripheral subtypes. The axial subtype is further divided into ankylosing spondylitis (AS) or radiographic axial spondyloarthritis and nonradiographic axial spondyloarthritis (nr-axSpA). Although AS and nr-axSpA share some common features, nr-axSpA lacks X-ray-based sacroiliitis as defined by the modified New York criteria, that is, the presence of either bilateral grade 2 sacroiliitis or unilateral grade 3 sacroiliitis, which is present in AS. Disease activity in either of them is measured via C-reactive protein (CRP) levels or magnetic resonance imaging (MRI) of the pelvis showing sacroiliitis due to the presence of bone marrow edema. A person with active disease can have normal CRP and MRI findings, especially in nr-axSpA. Immune system activation during inflammation has been shown to alter platelet maturation and morphology, as reflected by platelet indices. These platelet indices have been studied in the past in various autoimmune diseases, such as psoriatic arthritis, AS, and rheumatoid arthritis, and have been correlated with disease activity. Particularly, in spondyloarthritis, platelet indices are more central to the pathology of sacroiliitis, and CRP, which is currently used, is a generalized marker of inflammation. Therefore, platelet indices can provide a better understanding of inflammation, particularly in patients with sacroiliitis. OBJECTIVE: This study aims to investigate whether platelet indices can be better markers of inflammation in patients with nr-axSpA. We will determine whether platelet indices are reliable biomarkers for measuring disease activity in patients with nr-axSpA. METHODS: All patients who are classified as having axial spondyloarthritis as per the Assessment of Spondylarthritis International Society criteria will be included in this study. Patients will be divided into 2 case groups: group A (patients without radiographic sacroiliitis [nr-axSpA]) and group B (patients with radiographic sacroiliitis [AS]). Healthy individuals will be enrolled as controls to compare and correlate platelet indices such as platelet count, plateletcrit, mean platelet volume, and platelet distribution width with CRP, erythrocyte sedimentation rate, and MRI findings in patients with AS and nr-axSpA. RESULTS: This is a nonfunded study. The data collection started on February 1, 2025, and we expect to complete the study by December 2027. As of July 2025, 7 individuals had been enrolled in groups A and B, respectively, and 5 individuals had been included in the control group. At the end of the study, we will be able to correlate whether platelet indices are trustworthy biomarkers of active disease in patients with nr-axSpA. CONCLUSIONS: If platelet indices prove to be better markers of active disease in patients with nr-AxSpA, then these markers should be included in the routine evaluation of these patients. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): DERR1-10.2196/71909.