POS0672 AUTOANTIBODIES AND HIGH ATTENUATION AREAS ON HRCT IN EARLY RHEUMATOID ARTHRITIS
Authors: M. Loberg Haarhaus, J. Yu, K. Chatzidionysiou
Journal: Annals of the Rheumatic Diseases (2024)

<h3>Background:</h3> RA-associated interstitial lung disease (ILD) is a common extra-articular manifestation associated with increased mortality and can be subclinical in 20-60% of RA patients. It can occur at any time during the disease course, even before the development of arthritis. We have previously observed subclinical lung abnormalities on HRCT in around half of patients with early RA. Quantitative lung densitometry can be used to measure the density in hounsfiled units of each voxel of the lung parenchyma on CT scan. The percentage of voxels with high attenuation [percentage high attenuation area (%HAA)] has been shown to be a quantitative CT biomarker of subclinical ILD. (1). <h3>Objectives:</h3> To study whether HRCT findings and RA-autoantibodies are associated with %HAA on HRCT in early untreated RA. <h3>Methods:</h3> Newly diagnosed, untreated RA patients without lung symptoms underwent lung HRCT. Quantitative measures of lung parenchyma were made, and HAAs were defined as percentage of lung having an attenuation area between -600 and -250 Hounsfield units, a range that captures ground glass and reticular abnormalities. %HAA was defined as high or low, based on the median (4.3%). Total lung parenchyma was measured for %HAA but also separate measures were performed for the lower lobes. Pulmonary function tests (PFTs) were performed, and HRCT images were evaluated by an experienced radiologist for RA-ILD features. The HRCT findings were categorised as parenchymal (nodules larger than 3 mm, ground-glass opacities, opacities, fibrosis and emphysema) and airway abnormalities (bronchiectasis, air trapping and airway wall thickening). Serum was analysed for IgG and IgA anti-CCP2 and IgM and IgA RF using the fluoroenzyme immunoassay EliA. Continuous variables were compared using Mann-Whitney U test. Categorical variables were compared using Chi<sup>2</sup> test. Correlations of continuous variables were calculated using Spearman rho correlation coefficients. <h3>Results:</h3> %HAA was assessed in 106 RA patients. Median (IQR) %HAA was 4.3 (3.4 – 7.7). Only 7 patients had high %HAA defined as ≥10% of lung parenchyma. %HAA was similar in patients with HRCT parenchymal abnormalities and those without (4.3 (3.4 – 7.0) vs (4.6 (3.6 – 8.1), <i>p</i>=0.46). When we examined a subgroup of patients with fibrotic changes in HRCT (N=12), significantly more patients had a high %HAA (83%) compared to those without fibrotic changes (17%), (<i>p</i>=0.03). We found no significant association between anti CCP positivity or anti CCP titers between patients with high or low %HAA (Table 1). No correlation was found between CCP titers and %HAA however, when we examined the same correlation in the lower lobes a significant correlation was observed, though weak (r=0.20, <i>p</i>=0.05). RF positivity was associated with higher %HAA (<i>p</i>=0.01) (Table 1). This association was stronger for the RF IgM isotype (<i>p</i>=0.001) than for the IgA isotype (<i>p</i>=0.058). No correlation was observed between RF levels and %HAA (r=0.06, <i>p</i>=0.54). Regarding PFTs we observed a significant correlation between %HAA and FEV1/SVC (<i>p</i>=0.02) and a borderline significant correlation between %HAA and DLCO (<i>p</i>=0.06). <h3>Conclusion:</h3> HAA is a promising quantitative method to identify early RA-ILD. In this study we found an association between subclinical fibrotic changes in HRCT and %HAA. RF positivity, but not anti CCP positivity was associated with higher %HAA. <h3>REFERENCES:</h3> [1] Bernstein EJ, Barr RG, Austin JHM<i>, et al</i>. Rheumatoid arthritis-associated autoantibodies and subclinical interstitial lung disease: the Multi-Ethnic Study of Atherosclerosis. <i>Thorax</i> 2016;<b>71:</b>1082-1090. <b>Table 1.</b> <h3>Acknowledgements:</h3> <b>NIL.</b> <h3>Disclosure of Interests:</h3> Malena Loberg Haarhaus Boehringer-Ingelheim, Katerina Chatzidionysiou: None declared, Jimmy Yu: None declared.