Clinical, radiologic, and serologic predictors of rheumatic disease in interstitial lung disease patients.

Objective: Interstitial lung disease (ILD) can be the first manifestation of underlying rheumatic diseases. Identifying autoimmune features in ILD patients is crucial for early diagnosis and management. This study aims to evaluate the prevalence of rheumatic diseases in patients initially referred for ILD and to analyze their clinical, radiological, and serological characteristics.

Methods: A total of 181 patients referred to the rheumatology outpatient clinic with suspected ILD, who had no known history of a rheumatologic disease, were retrospectively analyzed. Patients without chest CT/HRCT scans (n = 38) and those without a confirmed ILD diagnosis after radiological re-evaluation (n = 44) were excluded. Demographics, clinical symptoms, serology, and imaging findings were compared between groups.

Results: Among the 99 ILD patients, 22 (22.2%) were diagnosed with a rheumatic disease following their ILD diagnosis. The most common rheumatic conditions were primary Sjögren's syndrome (n = 7), systemic sclerosis (n = 5), and rheumatoid arthritis (n = 5). The rheumatic disease-related ILD (RD-ILD) group had a significantly higher female predominance (77.3% vs. 34.7%, p < 0.001) and lower smoking prevalence (p = 0.006) compared to the non-RD-ILD group. Usual interstitial pneumonia was the most frequently observed chest CT/HRCT pattern in both groups. ANA, RF, and ACPA positivity was significantly higher in RD-ILD patients (p = 0.029, p = 0.003, and p = 0.001, respectively). Two patients met the IPAF classification criteria, both exhibiting NSIP patterns on chest CT/HRCT.

Conclusion: A substantial proportion of ILD patients were subsequently diagnosed with a rheumatic disease, highlighting the importance of routine autoimmune screening in ILD patients. Female predominance, lower smoking rates, and higher serological positivity in RD-ILD patients suggest that early rheumatologic evaluation could facilitate timely diagnosis and management.

Key points: • Interstitial lung disease may be the initial clinical sign of connective tissue diseases, highlighting the essential role of rheumatology in diagnosis and disease management.