Hospitalization Trends and Risk Factors in Rheumatoid Arthritis-Related Interstitial Lung Disease: An Observational Study From Ontario, Canada.

Abstract

Background: Rheumatoid arthritis-related interstitial lung disease (RA-ILD) represents an important disease manifestation of rheumatoid arthritis. A scarcity of population-level information on hospitalization rates in RA-ILD exists.

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 interstitial lung disease before 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 an 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 people between 2003 and 2022 (101% increase; P < .001). RA-ILD-related hospitalizations increased from 2.6 to 3.5 admissions per 100,000 people (37% increase; P = .045). In-hospital mortality from RA-ILD-related admissions was 19.5 deaths per 100 admissions in 2022, having remained stable over time (P = .62). Patients in the lowest income quintile (OR, 1.35 [95% CI, 1.06-1.72]; P = .02) and residing in rural areas (OR, 1.37 [95% CI, 1.11-1.70]; P = .004) were more likely to receive a diagnosis of RA-ILD during a hospitalization. Patients who received a diagnosis of RA-ILD during a hospitalization showed an increased hazard for future RA-ILD-related admissions (hazard ratio, 1.44 [1.24-1.68]; P < .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 an RA-ILD diagnosis in the hospital, which seems to be an important risk factor for future RA-ILD-related admissions.