The prevalence of interstitial lung disease in rheumatoid arthritis: a systematic review

Abstract Objectives Interstitial lung disease (RA-ILD) is an important comorbidity in rheumatoid arthritis. Its true prevalence remains unclear. We assessed reported prevalences across different diagnostic approaches. Methods We conducted a systematic literature review and meta-analysis to assess RA-ILD prevalence. Embase, Medline (Pubmed), Cochrane Library, and Web of Science were searched (inception-2022). Heterogeneity was assessed (I2). Subgroup differences were assessed (Q-test). Bias appraisal was performed via a funnel plot and Egger’s test. Individual studies were evaluated for the presence of bias, using the AXIS score. Mixed-effects meta-regression explored sample size, diagnostic modality, geography, and AXIS score as moderators. Results We included 74 studies and obtained an overall random-effect pooled prevalence of 20.6% (95% CI: 18.3–23.2%, I2=99.7%). The random-effects pooled prevalence varied by diagnostic method: 31% (95% CI: 25–38%, I2=97%) when using (HR)CT, 21% (95% CI: 14–31%,I2=95%) with PFTs, 13% (95% CI: 5–30%, I2=99%) when combining multiple diagnostic tools, 12% (95% CI: 7–20%, I2=96%) with chest X-ray, and 5% (95% CI: 4–8%, I2=100%) when based on ICD codes. Low-bias recent studies (AXIS 16; 2013–2022) yielded a pooled prevalence of 10.1% (95% CI: 6.2–16.3%; I2=99.9%). Prevalences significantly differed between tools (Q = 73.16, df = 4, p 0.0001). The meta-regression model (QM = 89.96, df = 11, p 0.0001) had a moderate explanatory value (R2 = 47.82%). The asymmetric funnel plot (t = 2.59, df = 98, p = 0.011) pointed to significant bias (estimate of 4.86, SE = 1.88). Conclusion Due to extreme heterogeneity and evidence of small-study effects, the overall pooled random-effects prevalence (20%) should be interpreted cautiously and primarily reflects the wide variation in diagnostic approaches. Estimates derived from low-bias and multimodal diagnostic studies (approximately 10–13%) may provide a more clinically meaningful approximation, though they remain informed estimates rather than definitive prevalence rates.