FRI0560 Quantitative ct indexes in the evaluation of interstitial lung disease related to rheumatoid arthritis

Background In. rheumatoid arthritis (RA), interstitial lung disease (ILD) is the most common pulmonary complication and it is associated with poor prognosis. The gold standard to detect ILD is the chest Computed Tomography (CT). CT semiquantitative scoring and quantitative methods are used to estimate the extension of ILD; however the first ones are time consuming and they have a considerable inter/intra-observer variability. Quantitative scores are based on the detection of the parameters of distribution of lung attenuation (also called quantitative CT indexes – QCTi). Previously a good correlation between QCTi calculated through an open-source program (OsiriX) and semi-quantitative score performed by experienced radiologists was demonstrated in a cohort of systemic sclerosis (SSc) patients. Furthermore, the QCTi were demonstrated to be able to discriminate between SSc subjects with different mortality risk based on ILD extent (<20% vs<20%) or lung functional values. Objectives. Main aim is to investigate if in RA-ILD there is a correlation between QCTi and semiquantitative scores. Secondary aims are: a) to verify if there is a difference of QTCi distribution in RA-ILD patients with severe vs mild ILD extent; b) to evaluate the discriminative ability of QTCi in identifying patients with severe ILD. Methods. Two experienced radiologists assessed the ILD on chest CT of 45 patients with RA according to the semiquantitative score proposed by Goh et al. ILD extent 20% were considered mild and severe, respectively. All CTs were blindly processed by a rheumatologist using OsiriX to obtain the QCTi (kurtosis, skewness, mean lung attenuation). The semiquantitative scores and the QCTi were correlated through the Spearman rank test. QCTi distribution and discriminative ability were, respectively, verified using Mann-Whitney test and ROC curves. Results. The majority of QCTi showed a statistically significant correlation of moderate degree (0,40<0,59) with the semiquantitative assessment (p-value<0.01). Patients with severe and mild ILD had dissimilar QCTi values (p<0.001). Among QCTi, kurtosis (tKurt) had the best discriminative ability (AUC=0.80, 95% CI 0.65 to 0.91, p<0.0001). The best tKurt cut-off value that identifies patients with severe pulmonary involvement was 3.67. Conclusions. In RA-ILD, QCTi correlate with the CT semiquantitative scores. Our preliminary findings suggest that RA-ILD severity is related to QCTi. Moreover a QCTi (tKurt) has a cut-off that can discriminate patients with severe ILD. So, QCTi may become simple tools to help the rheumatologist to quickly evaluate the severity of ILD in RA patients and estimate the prognosis.