The objective of the study was to identify risk factors for acute exacerbation of interstitial lung disease (ILD) during tocilizumab treatment in patients with rheumatoid arthritis (RA). This is a retrospective, case–control study. We reviewed 395 consecutive RA patients who received tocilizumab. First, we divided the patients according to the presence (RA-ILD) or absence of ILD (non-ILD) assessed by chest X-ray or high-resolution computed tomography, and compared them for characteristics relevant to RA-ILD. Subsequently, focusing on the patients with RA-ILD, we assessed their baseline characteristics and clinical courses comparing patients with acute exacerbation to those without. Comparing 78 with ILD and 317 without ILD, the following were identified as factors related to RA-ILD on multivariate analysis: age 60 years or older (OR 4.5, 95 % CI 2.2–9.4, P <0.0001), smoking habit (OR 2.9, 95 % CI 1.5–5.5, P = 0.002), and high rheumatoid factor levels (OR 2.8, 95 % CI 1.4–5.5, P = 0.002). Of 78 RA-ILD patients, six developed acute exacerbation during tocilizumab treatment. The median duration between the initiation of tocilizumab treatment and the acute exacerbation occurrence was 48 weeks. While baseline characteristics did not differ between acute exacerbation and non-acute exacerbation groups, patients experiencing acute exacerbation had significantly higher Clinical Disease Activity Index (CDAI) at 24 weeks (20.8 vs. 6.2, P = 0.019). Univariate analysis showed that CDAI > 10 at 24 weeks was a risk factor for acute exacerbation (OR 4.7, 95 % CI 2.1–10.4, P = 0.02). Uncontrolled arthritis activity during tocilizumab treatment may be associated with acute exacerbation of RA-ILD, suggesting post-treatment monitoring of disease activity is important not only with respect to RA itself but also for RA-ILD.
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