Coexistence of rheumatoid arthritis and systemic lupus erythematosus is still rare in the biologic era: Report of seven cases and literature review

To the Editor, Occasionally, we encounter patients who develop overlapping features of rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE), which is termed as 'rhupus syndrome' [1]. This syndrome is rare, with an estimated prevalence of 1% in patients with RA [2]. However, anti-tumor necrosis factor (TNF) inhibitor has been increasingly used for patients with RA and is currently listed as the most common cause of drug-induced lupus [3]. Therefore, it is possible that the prevalence of rhupus syndrome is increasing in the modern biologic era. From April 2018 to March 2019, 883 cases of RA were encountered at Osaki Citizen Hospital, and 150 of those cases were treated with anti-TNF inhibitors: 5 cases treated with infliximab, 76 with etanercept, 17 with adalimumab, 23 with golimumab, and 29 with certolizumab. Seven cases (0.8%, 7/883) were diagnosed as having rhupus syndrome (Table 1)....