POS1380 AUTOANTIBODIES ARE ASSOCIATED WITH EROSIVE DAMAGE IN THE SECOND AND THIRD METACARPOPHALANGEAL JOINTS ASSESSED BY HIGH-RESOLUTION PERIPHERAL QUANTITATIVE COMPUTED TOMOGRAPHY IN PATIENTS WITH RHEUMATOID ARTHRITIS.

Abstract

BackgroundThe presence of anti-citrullinated protein antibodies (ACPAs) and rheumatoid factor (RF) are prognostic for erosive severity by radiography in patients with rheumatoid arthritis (RA) [1]. However, others have shown that RF mainly acts as an enhancer for ACPAs mediated bone loss [2]. High-resolution peripheral quantitative computed tomography (HR-pQCT) has a very high resolution with a voxel size of 82 µm3, and has been proposed to monitor disease activity in patients with RA. In the current study, erosive damage was assessed by HR-pQCT according to the presence of autoantibodies. The hypothesis is that the presence of RF and especially ACPA is associated with erosive damage in two metacarpophalangeal (MCP) joints assessed by HR-pQCT; this has previously been shown using 44 joints assessment of both hands and feet by conventional radiography.ObjectivesThe objective was to investigate if the presence of the autoantibodies, RF and ACPAs, was associated with a higher erosive burden in two MCP joints assessed by HR-pQCT.MethodsPatients with RA and disease duration ≥ 5 years had their second and third MCP joints imaged by HR-pQCT. Age, sex, disease duration, ACPAs and RF status were acquired. From the Danish Clinical Quality Program – The Danish Rheumatologic Database (DANBIO) [3], the average 28-joint Disease Activity Score (DAS28-CRP) and Health Assessment Questionnaire (HAQ) from five years before inclusion were extracted. Statistical significance was investigated for the following groups, who were ordered according to the expected erosive burden: RF+/ACPA+ patients, RF-/ACPA+ patients, RF+/ACPA- patients, and autoantibodies negative patients. Analysis of variance was used to investigate the difference between the groups for age and sex. Cuzick’s Rank-sum test for trend of ordered groups was used to test for trend for disease duration, 5-year average HAQ, 5-year average DAS28, number of erosions, total erosive volume, and average erosion volume.ResultsA total number of 353 patients with RA were included in this study. 203 was RF+/ACPA+ positive, 52 was RF-/ACPA+ positive, 24 were RF+/ACPA- positives, and 74 were autoantibodies negative. The groups were comparable with respect to age, sex distribution, disease duration and mean disease activity during the last five years, according to mean DAS28-CRP and mean HAQ during the previous five years.There was a statistically significant test for trend for total erosive volume (p = 0.016) and average erosion volume (p = 0.043), but not for the number of erosions (p = 0.053) (Figure 1). A significant difference between the groups was only observed between double-positive patients and patients negative for autoantibodies.Figure 1.Scatterplot showing the number of erosions (A), total erosive volume (B) and the average volume of erosions (C) in the second and third MCP joint per patient according to the presence of the autoantibodies, ACPAs, as well as RF. Boxes denote the median and 25th and 75th percentile of the groups.ConclusionIn the current study, HR-pQCT scanning of only two MCP joints supports previous findings by radiography of both hands and feet, showing the accumulated erosive burden is higher in patients double-positive for RF and ACPA.