Correspondence on: 'EULAR definition of difficult-to-treat rheumatoid arthritis'.

Competing Interests: Competing interests: AB reports grants and personal fees from AbbVie, Pfizer, Novartis and Roche; personal fees from Amgen, Sandoz, Lilly and UCB; personal fees and non-financial support from BMS; and grants, personal fees and non-financial support from Nordic, outside the submitted work. IM reports personal fees from Roche, outside the submitted work. DP reports grants from AbbVie, Lilly, MSD and Roche, outside the submitted work. AV reports grants from AbbVie, Janssen and Bristol Myers, outside the submitted work. VN-C reports grants from AbbVie, Janssen, Lilly, Novartis, Pfizer and UCB Pharma.