Objectives Biological therapy represents important advances in alleviating rheumatoid arthritis (RA), but the effect on interstitial lung disease (ILD) has been controversial. The objective of this study was to assess the risk of such treatment for patients with ILD.

Design Case–control cohorts.

Setting Single centre in Japan.

Participants This study included 163 patients with RA who underwent biological therapy.

Outcome measured We assessed chest CT before initiation of biological therapy and grouped 163 patients according to the presence of ILD (with (n=58) and without pre-existing ILD (n=105)). Next, we evaluated serial changes of chest CT after treatment and visually assessed the emergence of ILD or its progression, which was referred to as an ‘ILD event’. Then, we also classified the patients according to the presence of ILD events and analysed their characteristics.

Results Tumour necrosis factor (TNF) inhibitors were administered to more patients with ILD events than those without ILD events (88% vs 60%, p<0.05), but recipients of tocilizumab or abatacept did not differ in this respect. Of 58 patients with pre-existing ILD, 14 had ILD events, and that proportion was greater than for those without pre-existing ILD (24% vs 3%, p<0.001). Of these 14 patients, all were treated with TNF inhibitors. Four patients developed generalised lung disease and two died from ILD progression. Baseline levels of KL-6 were similar in both groups, but increased in patients with ILD events.

Conclusions TNF inhibitors have the potential risk of ILD events, particularly for patients with pre-existing ILD, and KL-6 is a valuable surrogate marker for detecting ILD events. Our data suggest that non-TNF inhibitors are a better treatment option for these patients.