Characterization of Spinal Pathology in Axial Psoriatic Arthritis - Abstract Axial psoriatic arthritis (AxPsA), that is psoriatic arthritis (PsA) with involvement of the joints and ligaments of the spine, is a sequel of chronic inflammation of the PsA disease process. The spectrum and nature of inflammation in AxPsA is not fully understood, and therefore the condition is often misdiagnosed or underdiagnosed. Current evidence suggests that axial entheseal soft-tissue-associated pathology is likely to be the dominant pathology in AxPsA, compared to osteitis in ankylosing spondylitis (AS). These soft tissues involved in PsA spinal pathology are relatively avascular structures compared with tissues such as the bone/synovium and are therefore a ‘blind spot’ for current imaging technology. Positron emission tomography (PET), as a molecular imaging modality, has potential to interrogate these tissues directly, however, it has not been exploited for this application, due to concerns associated with dose, spatial resolution and scan time. Recently, total-body PET/CT technology has been introduced that may address these concerns. Indeed, in our preliminary studies, we utilized this technology and visualized and quantified spinal enthesitis as a dominant pathology in majority of the evaluated study participants with PsA. Based on these observations, our central hypothesis is that TB-PET/CT measures will (1) offer a unique insight of the pathology of AxPsA in vivo, and (2) provide biomarkers that will associate with the total spinal inflammatory burden in PsA. To test this hypothesis, our study has two proposed aims. Our first aim will characterize the inflammatory pathologies underlying AxPsA in vivo. We will derive consolidated, whole-spine measures from TB- PET/CT, as surrogate, in vivo measures of inflammatory pathology and establish their discriminatory power against those derived from participants with AS. Our second aim will quantify the total spinal inflammatory load in AxPsA via TB-PET/CT, and compare it with standardized outcome measures and MRI evaluation of spinal pathology. This study will assess the performance of TB-PE/CT to identify pathologies associated with spinal inflammation in AxSpA, quantify the total spinal inflammatory load, and perform comparison of resulting metrics with those derived from participants with AS. If successful, this study will contribute novel, objective and quantifiable TB- PET/CT imaging metrics (biomarkers) of spinal inflammation in PsA. Data collected will provide robust sample size estimates and feasibility measures for informing future clinical studies (observational and interventional trials), using the proposed imaging measures as outcome or surrogate measures.
