Hospitalization trends and risk factors in rheumatoid arthritis related interstitial lung disease: an observational study from Ontario, Canada

Background — Rheumatoid arthritis related interstitial lung disease (RA-ILD) represents an important disease manifestation of RA. There is a scarcity of population level information on hospitalization rates in RA-ILD.

Research question — What are the current rates and trends in all-cause and RA-ILD related hospitalizations in patients with RA-ILD?

Study design and methods — We performed a retrospective observational study using health services data from Ontario, Canada between 2003 and 2022. We identified people with RA-ILD using the Ontario Rheumatoid Arthritis Database and required repeated physician claims for ILD prior to cohort entry. We estimated age- and sex-standardized annual all-cause and RA-ILD related hospitalization rates during the study period. We performed multivariable logistic regression to ascertain factors associated with a RA-ILD diagnosis during a hospitalization and generated a Fine-Gray subdistribution hazards model with competing risk to assess the time to RA-ILD related hospitalization.

Results — We identified 7,075 people with RA-ILD during the cohort period. Standardized all-cause hospitalization rates increased from 6.4 to 12.9 admissions per 100,000 population between 2003 and 2022 (101% increase, p<0.001). RA-ILD related hospitalizations increased from 2.6 to 3.5 admissions per 100,000 (37% increase, p=0.045). In-hospital mortality from RA-ILD related admissions was 19.5 deaths per 100 admissions in 2022, having remained stable over time (p=0.62). Patients in the lowest income quintile [OR 1.35 (1.06-1.72), p=0.02] and residing in rural areas [OR 1.37 (1.11-1.70), p=0.004] were more likely to be diagnosed with RA-ILD during a hospitalization. Patients diagnosed with RA-ILD during a hospitalization had an increased hazard for future RA-ILD related admissions [HR 1.44 (1.24-1.68), p<0.001].

Interpretation — All-cause and RA-ILD related hospitalizations are increasing. In-hospital mortality has not changed over time but remains substantial. Socioeconomic factors are associated with receiving a RAILD diagnosis in hospital, which appears to be an important risk factor for future RA-ILD related admissions.