We aimed to investigate the effect of intravenous cyclophosphamide (CYC) as the initial therapy in patients with acute exacerbation of rheumatoid arthritis-related interstitial lung disease.

This was a retrospective observational study. Using the Japanese Diagnosis Procedure Combination inpatient database from July 2010 to March 2018, we identified patients with acute exacerbation of rheumatoid arthritis-related interstitial lung disease (RA-ILD) who received high-dose methylprednisolone within 3 days after admission. RA-ILD was defined as having either the diagnosis of RA-ILD or the diagnoses of both RA and ILD, based on the ICD-10 codes recorded by attending physicians. Patients were divided into two groups: those receiving intravenous CYC within 3 days after admission (CYC group) and those who did not (control group). One-to-four propensity-score matching analyses were performed.

A total of 6130 eligible patients were included. After propensity score matching, 129 patients in the CYC group and 516 patients in the control group were further analyzed. 90-day in-hospital mortality, defined as all-cause mortality during hospitalization within 90 days after admission, was not significantly different between the CYC and control groups (50.4% versus 42.2%, hazard ratio 1.20, 95% confidence interval 0.91–1.58). A larger proportion of patients in the CYC group received platelet transfusion than that in the control group (7.0% versus 2.3%, odds ratio 3.05, 95% confidence interval 1.20–7.73).

In this retrospective database study, the initial therapy with CYC did not show a survival benefit in patients with acute exacerbation of RA-ILD. CYC was associated with a larger proportion of platelet transfusion.