Pos0871 role of inflammatory burden and treatment on joint space width in psoriatic arthritis-a high-resolution peripheral quantitative computed tomography study

Background Psoriatic Arthritis (PsA) is associated with enthesitis and synovitis which lead to bone erosions, cartilage loss, and new bone formation. High-resolution peripheral quantitative computed tomography (HR-pQCT) enables the quantitative 3D assessment of joint space width (JSW) with superior resolution compared to radiography. Whether disease-specific parameters are associated with JSW on HR-pQCT in PsA remains uncertain. Objectives To assess HR-pQCT joint space outcomes by comparison with radiographs and investigate the relationship between disease-related variables and JSW on HR-pQCT in PsA patients. Methods PsA patients who underwent HR-pQCT examination (XtremeCT I, SCANCO Medical AG, Brüttisellen, Switzerland) of the second to fourth metacarpophalangeal joint (MCPJ 2-4) were recruited in this cross-sectional study. The joint space metrics included joint space volume (JSV), mean, minimum (Min) and maximum (Max) JSW, JSW asymmetry (Asymm) and distribution (SD). Volumetric joint space was quantified using an algorithm developed by consensus from the Study group for eXtreme Computed Tomography in Rheumatoid Arthritis (SPECTRA). The joint space domain on standard radiography was scored using the Sharp/van der Heijde (SvdH) joint space score. A generalized estimating equation (GEE) was used to estimate the ability of HR-pQCT to predict SvdH scores. Linear regression models were used to determine the association between disease-related variables and JSW. Results 67 patients [47 (55.2%) males; median age: 57.0 (53.0, 63.0); median disease duration: 21 (16, 28) years] were included in this analysis. Most had mild disease activity [Disease Activity index for PsA (DAPSA): 10.1 ± 6.6]. 56/67 (84%) were on conventional synthetic disease modifying anti-rheumatic drugs (csDMARDs) while 27/67 (40%) were on biologic DMARDs (bDMARDs). 11 MCPJ 2, 9 MCPJ 3 and 7 MCPJ 4 were excluded due to poor image quality. Individual MCP joint space parameters were presented in Table 1. Subluxations were detected more frequently by HR-pQCT than radiographs. SvdH score was negatively associated with a lower mean, Max and Min JSW; and higher JSW SD and Asymm (all p<0.05). Multivariable linear regression analysis showed that males had larger JSV (MCPJ 2-4), mean (MCPJ 4) and Max JSW (MCPJ 3). Longer disease duration (MCPJ 2-3) and higher ESR level (MCPJ 3) were negatively associated with mean and Max JSW, while higher damage joint count was negatively associated with mean and Min JSW (MCPJ 2) (Figure 1). Use of csDMARDs was negatively associated with Min JSW (MCPJ 3); while use of bDMARDs was positively associated with Min JSW (MCPJ 2). Conclusion HR-pQCT could be widely used for assessing joint damage prior to evidence of radiographic joint damage in PsA patients. Higher inflammatory burden as reflected by longer disease duration, higher ESR levels, and damage joint count was negatively associated with mean, Max, and Min JSW, while suppression of inflammation using bDMARDs seems to prevent a decline in JSW. Table 1. Joint space analysis in PsA patients JS parameters MCPJ 2 MCPJ 3 MCPJ 4 JS volume (mm 3 ) 87.1 ± 18.8 94.1 ± 22.7 66.1 ± 15.0 Mean JSW (mm) 1.8 ± 0.2 1.7 ± 0.2 1.6 ± 0.2 JSW SD (mm) 0.3 (0.3, 0.3) 0.3±0.0 0.3±0.1 Max JSW (mm) 2.9 (2.7, 2.9) 2.7 (2.5, 2.9) 2.6 (2.5, 2.7) Min JSW (mm) 1.1 (0.8, 1.4) 1.1 (0.2, 1.3) 1.0 (0.9, 1.2) JSW Asym 2.4 (2.1, 3.2) 2.5 (2.2, 15.8) 2.4 (2.1, 3.0) PsA, psoriatic arthritis; MCPJ, metacarpophalangeal joint; JS, joint space; JSW, joint space width; SD, standard deviation; Max JSW, maximum JSW; Min JSW, minimum JSW; Asym, joint asymmetry. Figure 1. Forest plot demonstrating multivariable linear regression analysis between demographic and disease-related variables and JSW parameters at MCPJ 2 to 4 A, Joint space volume; B, Mean joint space width (JSW); C, Maximum JSW; D, Minimum JSW. MCPJ, metacarpophalangeal joint; ESR, erythrocyte sedimentation rate; csDMARDs, conventional synthetic disease-modifying anti-rheumatic drugs; bDMARDs, biologic disease-modifying anti-rheumatic drugs. Acknowledgements We are immensely grateful to patients, physicians, and the study personnel. Disclosure of Interests None Declared.