Risk factors for herpes zoster in Korean patients with rheumatoid arthritis treated with JAK inhibitor: a nested case–control study

OBJECTIVE: To determine the risk of herpes zoster (HZ) in Korean patients with rheumatoid arthritis (RA) receiving Janus kinase inhibitors (JAKis). METHODS: We performed a nested case–control study with 1:10 matching for sex and age using single-centre prospective cohorts of patients with RA receiving targeted therapy in Korea. Then we performed conditional logistic regression analyses to determine the risk associated with JAKi use compared with biologic disease-modifying antirheumatic drug (bDMARD) use, with adjusting for various factors. We also used logistic regression analysis to identify other risk factors for the development of HZ in JAKi users. RESULTS: From a total of 1147 patients, 61 cases and 610 matched controls were selected. In conditional logistic regression analysis, JAKi use did not increase the risk of HZ development (OR 1.35, 95% CI 0.70 to 2.61) after adjusting for other factors. Rather, duration of RA less than 10 years (OR 0.54, 95% CI 0.30 to 0.97) and having had three or more previous targeted therapies (OR 5.29, 95% CI 1.45 to 19.31) were risk factors for HZ. Among JAKi users, higher disease activity score 28-erythrocyte sedimentation rate (DAS28-ESR) (OR 1.44, 95% CI 1.06 to 1.97) was identified as a risk factor in addition to three or more previous targeted therapies (OR 10.12, 95% CI 1.92 to 53.49). CONCLUSIONS: The number of previous targeted therapies, but not JAKi use, was identified as a risk factor for HZ development in Korean patients with RA in a real-world setting. High disease activity was an additional risk factor for JAKi users.