Lung ultrasound in patients with rheumatoid arthritis: definition of significant interstitial lung disease

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).

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.

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.

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.