SAT0070 LUNG ULTRASOUND IN PATIENTS WITH RHEUMATOID ARTHRITIS AND THE DEFINITION OF SIGNIFICANT INTERSTITIAL LUNG DISEASE

Abstract

Background:In recent years, a growing interest has grown around interstitial lung disease (ILD) in patients with rheumatoid arthritis (RA). While high resolution computed tomography (HRCT) of the chest remains the diagnostic method of choice, increasing attention has been directed towards lung ultrasound (LUS) in the diagnosis of ILD in connective tissue diseases. LUS allows the detection of artifacts (B-lines) characteristic of ILD, without the need to use ionizing radiation. However, it is not yet well defined how to interpret the LUS findings under suspicion of RA-ILD.Objectives:To determine the cut-off number of LUS B-lines that identifies a significant RA-ILD.Methods:A cross sectional study was conducted on consecutive RA patients with suspected RA-ILD. The inclusion criteria were clinical (dyspnea, velcro sounds), instrumental (suggestive anomalies on conventional radiography, DLco reduction), or in presence of at least two of the following risk factors for RA-ILD: smoking habit, male sex, advanced age, and ACPA presence.Patients underwent LUS, chest HRCT, pulmonary function tests, and clinical evaluation. The diagnosis of RA-ILD was based on a semi-quantitative evaluation of HRCT using a computer-aided method (CaM). The 10% of fibrosis, measured with this method, was considered as a cut-off for the presence of significant RA-ILD. The LUS was carried out in 14 defined intercostal spaces using a linear multifrequency probe 6-18 MHz (MyLab Class C, Esaote S.p.A., Genoa, Italy) and the number of B-lines present in each intercostal space was counted and summed up (Figure 1). The discriminating validity of the LUS versus HRCT has been studied by using the receiver operating characteristic (ROC) curve analysis.Figure 1.LUS B-line illustrative.Results:72 consecutive RA patients (21 male, 51 female) were evaluated, with a mean age of 63.0 (SD 11.5 years), a mean ACPA titre of 327.6 (SD 633.3) U/ml and a rheumatoid factor of 324.6 (SD 748.7) U/ml. The mean estimate of pulmonary fibrosis using the CaM was 11.2% (SD 7.5) at HRCT, while at LUS the mean number of B-lines was 10.6 (SD 15.1). Pulmonary fibrosis of 10% as measured by the CaM at HRCT was detected in 25 patients (34.72%). Applying this HRCT cut-off point as an estimate of significant fibrosis, the presence of 9 B-lines was found to be the optimal cut-off at ROC curve analysis. This LUS cut-off defines the presence of significant fibrosis with a sensitivity of 70.0%, a specificity of 97.62%, and a positive likelihood ratio of 29.4 (Figure 2).Figure 2.Area under the ROC curve to determine the number of B-lines at LUS to define a significant RA-ILD, applying the 10% of fibrosis at chest HRCT measured by OsiriX as external criterion.Conclusion:The present study provided data to determine the number of B-lines to identify a significant RA-ILD. LUS may represent a useful technique to select RA patients to be assessed by chest HRCT.