How can I differentiate between rheumatoid lung disease and other causes of interstitial lung disease in a patient with RA?

In a patient with rheumatoid arthritis (RA), differentiating rheumatoid lung disease (specifically RA-associated interstitial lung disease, RA-ILD) from other causes of interstitial lung disease (ILD) involves a combination of clinical, radiological, serological, and histopathological assessments. Clinically, RA-ILD often presents with progressive dyspnoea and dry cough in the context of established RA, but other ILDs may have overlapping symptoms, so detailed history including medication exposure and smoking status is essential ¹. Serologically, high titres of rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) antibodies support RA-ILD but are not definitive for lung involvement alone (Atzeni et al., 2018). Radiologically, high-resolution computed tomography (HRCT) is critical: RA-ILD commonly shows patterns such as usual interstitial pneumonia (UIP) or nonspecific interstitial pneumonia (NSIP), with UIP pattern being more frequent and associated with worse prognosis ¹; other ILDs may show different HRCT patterns or distribution. Histopathology from lung biopsy, if performed, can confirm the pattern of fibrosis and inflammation characteristic of RA-ILD, distinguishing it from other ILDs like idiopathic pulmonary fibrosis or hypersensitivity pneumonitis (Schulte and Husain, 2020). Additionally, exclusion of other causes such as drug-induced lung disease, infection, or malignancy is necessary through appropriate investigations ¹. Emerging precision medicine approaches, including molecular biomarkers and genetic profiling, may further aid differentiation in the future (Matson, 2025). Thus, an integrated approach combining clinical context, serology, HRCT pattern recognition, and, when needed, histopathology is essential to differentiate RA lung disease from other ILDs in RA patients ¹; (Atzeni et al., 2018); (Schulte and Husain, 2020); (Matson, 2025).