Interstitial lung disease in systemic autoimmune rheumatic diseases: radiologic and histologic correlations

Abstract Objectives High-resolution CT (HRCT) guides clinical diagnosis in systemic autoimmune rheumatic disease (SARD) associated interstitial lung disease (ILD). Histologic confirmation by lung biopsy is not commonly done. We aimed to evaluate HRCT-explant pathology agreement in transplanted SARD-ILD patients. Methods We retrospectively analyzed all idiopathic inflammatory myopathy (IIM), systemic sclerosis (SSc) and rheumatoid arthritis (RA)-ILD patients who underwent double lung transplant at two Canadian centres from 2012 to 2024. HRCT-histology agreement was assessed using weighted kappa (κ) statistics. Results were visualized via alluvial step-by-step diagrams. Results Among 82 patients (22 IIM, 32 SSc, 28 RA) who underwent lung transplant, RA patients were older, more often smokers and less frequently female than IIM/SSc. IIM patients most commonly required emergency transplantation. Initial HRCT showed NSIP predominance in IIM (59%) and SSc (81%), while UIP dominated in RA (57%). Explant pathology revealed NSIP as the primary pattern in SSc (62%) and UIP in RA (50%). IIM explants exhibited diverse histopathology without dominance. Using weighted κ analysis, we observed moderate HRCT-histology concordance in RA (κ = 0.46, P = 0.002), fair but non-significant agreement in SSc (κ = 0.31, P = 0.06), and no meaningful correlation in IIM (κ = 0.07, P = 0.6). Anti-MDA5+ IIM patients universally developed rapidly progressive ILD, progressing to diffuse alveolar damage or end-stage fibrosis despite initial NSIP on HRCT. Conclusion SSc-ILD and RA-ILD demonstrated fair-to-moderate HRCT-histology correlation, whereas IIM-ILD shows marked histologic heterogeneity independent of imaging patterns. Anti-MDA5+ disease consistently exhibited aggressive progression, underscoring the limitations of HRCT in predicting IIM-ILD pathology.