Objectives: The aim of this study was to determine the cut-off number of lung ultrasound (LUS) B-lines that identifies a significant rheumatoid arthritis-interstitial lung disease (RA-ILD). Methods: RA patients with suspected RA-ILD were consecutively enrolled. Patients underwent LUS (carried out in 14 defined intercostal spaces), chest HRCT, pulmonary function tests, and clinical evaluation. The diagnosis of RA-ILD was based on a semi-quantitative evaluation of chest HRCT using a computer-aided method (CaM). The discriminative validity of the LUS versus HRCT has been studied by using the receiver operating characteristic (ROC) curve analysis. Results: 72 consecutive RA patients (21 male, 51 female) were evaluated, with a mean age of 63.0 (SD 11.5 years). The mean estimate of pulmonary fibrosis using the CaM was 11.20% (SD 7.48) at chest HRCT, while at LUS the mean number of B-lines was 10.65 (SD 15.11). A significant RA-ILD, as measured by the CaM at HRCT, was detected in 25 patients (34.7%). 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 RA-ILD with a sensitivity of 70.0%, a specificity of 97.62%, and a positive likelihood ratio of 29.4. Conclusions: 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.
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