Concomitant methotrexate has little effect on clinical outcomes of abatacept in rheumatoid arthritis: a propensity score matching analysis.

• This is the first study to directly compare the clinical efficacy and safety of abatacept between patients with and without concomitant methotrexate (MTX) treatment in 'real-world' settings using the propensity score matching method. • There were no significant differences in clinical outcomes of abatacept between patients with and without concomitant MTX treatment. • We used data from a large Japanese multicentre registry for biologics in rheumatoid arthritis, thereby decreasing selection bias based on the personal preferences of physicians.