Detection of Interstitial Lung Disease in Rheumatoid Arthritis by Thoracic Ultrasound. A Diagnostic Test Accuracy study.

OBJECTIVE: The Objective was to determine the diagnostic accuracy of thoracic ultrasound (TUS) for detecting (ILD) in rheumatoid arthritis (RA) with respiratory symptoms.

METHODS: Individuals with RA visiting Rheumatological outpatient clinics in the Region of Southern Denmark were systematically screened for dyspnoea, cough, recurrent pneumonia, prior severe pneumonia or a chest X-ray indicating interstitial abnormalities. Eighty participants with a positive screening were consecutively included. Individuals were not eligible if they had a chest high-resolution CT (HRCT) <12 months or were already diagnosed with ILD. A blinded TUS expert evaluated TUS, and TUS was registered as positive for ILD if ≥10 B-lines or bilateral thickened and fragmented pleura were present. The primary outcomes were TUS's sensitivity, specificity, and positive predictive value (PPV) and negative predictive value (NPV). An ILD-specialised thoracic radiologist assessed HRCT, followed by a multi-disciplinary team discussion, which was the reference standard. The accepted window of HRCT was <30 days after TUS was performed.

RESULTS: 77 participants received HRCT <30 days after TUS, and 23 (30%) were diagnosed with ILD. TUS had a sensitivity of 82.6% (95% CI: 61.2% to 95.0%) and a specificity of 51.9% (95% CI: 37.8% to 65.7%), corresponding to a PPV of 42.2% (95%CI 27.7% to 57.8%) and an NPV of 87.5% (95% CI 71.0% to 96.5%).

CONCLUSION: To our knowledge, this prospective study is the first to use respiratory symptoms in RA as inclusion criteria. Systematic screening for respiratory symptoms combined with TUS can reduce the diagnostic delay of ILD in RA.