OP0052 Cortical bone loss is an early feature of axial spondyloarthritis

Background Systemic bone loss is a well-known and severe consequence in axial spondyloarthritis (axSpA). To date deterioration of bone microstructure has only been described in patients with long-standing ankylosing spondylitis while bone microstructure has not been assessed in axSpA. Objectives The aim of the present study was to investigate bone microstructure, geometry and volumetric bone mineral density (vBMD) using high resolution peripheral quantitative CT (HR-pQCT) in a cohort of axSpA patients at an early stage of disease and to search for potential factors for deterioration of bone microstructure. Methods An inception cohort of 101 axSpA patients and 50 healthy controls of similar age and sex was assessed for geometric, volumetric and microstructural parameters of bone using HR-pQCT scanning of the radius. Additionally, demographic and disease specific characteristics of SpA patients were recorded. Results SpA patients and controls were comparable in age (median (IQR) 45.0 (15.0) vs. 44.76 (26.0) years, p=0.917), sex (female 41.6% vs. 40%, p=0.852) and BMI (median (IQR) 26.3 (6.5) vs. 23.8 (5.2), p=0.118). 75% of patients showed HLA-B27 positivity. Median disease duration was 6.5 (9.0) years, 58.4% of patients were on biological treatment and 14.9% of patients in disease remission according to ASDAS-CRP. Geometric and microstructural analysis by HR-pQCT revealed a significantly reduced cortical area (p=0.022) and cortical thickness (p=0.006) in SpA patients compared to controls. No differences in cortical porosity (p=0.685), trabecular geometry or microstructure were detected. Total and cortical vBMD were significantly reduced in SpA patients (p=0.042 and p=0.007), while there was no difference in trabecular vBMD (p=0.376). Patients with a short disease duration 2 years (n=55) additionally developed a decrease of cortical and total vBMD (p=0.004 and p=0.036). Multivariate regression models identified male sex to be associated with lower cortical vBMD and female sex with lower trabecular vBMD. History of prednisolone treatment (>5mg >3months) was associated with lower trabecular vBMD, and disease duration with higher trabecular vBMD. Remission status, treatment with TNF inhibitors, HLA-B27 status and presence of peripheral arthritis did not influence bone microstructure independently. Conclusions Bone microstructure in SpA patients is primarily characterized by deterioration of cortical bone. Cortical bone loss starts early and is evident within the first 2 years of disease. Disclosure of Interest None declared