Using Thoracic Ultrasound to Detect Interstitial Lung Disease in Patients With Rheumatoid Arthritis

Background: Pulmonary diseases are significant contributors to morbidity and mortality in patients with rheumatoid arthritis (RA). One of the most common pulmonary manifestation in RA is interstitial lung disease (RA-ILD). Consequently, RA-ILD may be prevalent in approximately 30% and clinically evident in about 10% of RA patients. Since the median survival for patients with manifest RA-ILD is only 6.6 years, feasible methods of detecting early RA-ILD are warranted.

Objectives: To determine the diagnostic accuracy of thoracic ultrasound (TUS), using a 14-zone protocol, for ILD in RA patients with respiratory symptoms by using chest high-resolution computed tomography (HRCT) as the reference standard. The secondary aim is to evaluate the diagnostic accuracy for the blood biomarkers surfactant protein-D (SP-D) and microfibrillar-associated protein 4 (MFAP4) in the detection of ILD in this group of patients.

Data collection: Participants will be included after signing the informed consent; data will be collected and stored in a REDCap database.

Eligibility criteria for participants and settings where data will be collected: Patients eligible for inclusion are consenting adults (≥18 years) diagnosed with RA (according to the 2010 ACR-criteria for RA) and respiratory symptoms indicating RA-ILD, based on the presence of at least one of the following symptoms: unexplained dyspnoea, unexplained cough and/or a residual pneumonia or a chest X-ray indicating interstitial abnormalities in the lung.

Whether participants form a consecutive, random or convenience series: Participants form a consecutive series of up to 80 individuals in total.

Description of the index test and reference standard: Patients suspected of having RA-ILD will undergo a 14 zone TUS as index test performed by a junior resident in rheumatology, who is certified by the European Respiratory Society in performing TUS assessment. The anonymised images will be stored, and scored by the junior resident and two senior rheumatologists, who have also received training in TUS, as well as a TUS and ILD experienced pulmonologist. Chest HRCT will be the gold standard, i.e. the ILD reference standard.

Estimates of diagnostic accuracy and their precision: The two basic measures for quantifying the diagnostic accuracy of the TUS (index) test are the sensitivity and specificity in comparison to the chest HRCT. Statistical tests will be conducted using the McNemar test for correlated proportions.