Incidence and prevalence of connective tissue disease (CTD)-associated interstitial lung disease in the United States

Objectives Interstitial lung disease (ILD) is a pulmonary manifestation of connective tissue diseases (CTDs). Limited data exist describing the epidemiology of CTD-ILD; therefore, this study aimed to estimate the incidence and prevalence of CTD-ILD in the US, overall and by CTD-ILD subtypes. Methods Patients with CTD-ILD and rheumatoid arthritis (RA), systemic sclerosis (SSc), systemic lupus erythematosus (SLE), idiopathic inflammatory myopathy (IIM), mixed CTD (MCTD), and Sjögren’s disease (SjD) were identified from Optum ® de-identified Electronic Health Record data set (Optum ® EHR) and MarketScan ® Commercial and Medicare US databases between 2019 and 2024. Results ILD was present in 4.3% (n = 21,366/496,690; Optum ® EHR) and 3.2% (n = 7521/234,468; MarketScan) of identified patients with CTD. This proportion was highest for those with SSc (Optum ® EHR: 20.3%; MarketScan: 21.1%). Most patients with CTD-ILD were female in both Optum ® EHR and MarketScan, with median ages 64 and 56 years, respectively; race was available only in Optum ® EHR, where 72.1% were categorized as Caucasian. Age- and sex-adjusted incidence rates were 7.6 and 10.0 per 100,000 person-years, with adjusted prevalence rates 46.7 and 43.4 per 100,000 persons. Rates varied by CTD subtype and were highest for RA-ILD and lowest for MCTD-ILD across databases. Crude rates of CTD-ILD regardless of subtype were higher among female patients, patients aged ≥ 65 years, and among patients of Black African ancestry. Conclusion Consistent age- and sex-adjusted CTD-ILD incidence and prevalence estimates between two large, demographically distinct US databases provide contemporary population-level estimates of CTD-ILD frequency and distribution that can inform disease screening and patient care. Key points • US CTD-ILD incidence estimated at 7.6 and 10.0/100,000 person-years and prevalence estimated at 46.7 and 43.4/100,000 persons. • Incidence and prevalence rates were highest in female patients, patients aged ≥ 65 years, and patients of Black African ancestry. • Incidence and prevalence rates varied between CTD subtypes and were highest for RA-ILD and lowest for MCTD-ILD.