Successful treatment of rheumatoid arthritis‐associated <scp>interstitial lung disease</scp> with filgotinib: A case report on <scp>janus kinase 1</scp> inhibition

Filgotinib, a janus kinase 1 (JAK1) inhibitor, is used in the treatment of rheumatoid arthritis (RA). RA-associated interstitial lung disease (RA-ILD) is a severe RA complication with no established effective treatment. We report the case of a patient with RA-ILD successfully treated with filgotinib. A 46-year-old woman with RA and RA-ILD, presenting with a non-specific interstitial pneumonia pattern, was refractory to abatacept and prednisolone but responded to filgotinib. Both arthritis and RA-ILD improved significantly, and the patient remained in remission for over 12 months. Basic research indicates that JAK1 plays a role in the cytokine signal transduction in ILD; however, there are no clinical reports on the efficacy of filgotinib in RA-ILD. This case suggests filgotinib as a potential treatment for patients with RA-ILD, particularly in the early stages of this disease.