Risk of Autoimmune Rheumatic Diseases in Multiple Sclerosis and Neuromyelitis Optica Spectrum Disorder: A Nationwide Cohort Study in South Korea

Objective: To investigate the risk of autoimmune rheumatic diseases (ARDs) in multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD) compared with a control population using the Korean National Health Insurance Service database. Patients and Methods: The MS/NMOSD cohorts were collected from patients registered in the Korean National Health Insurance Service database between January 1, 2010, and December 31, 2017, using the International Classification of Diseases, Tenth Revision diagnosis codes and information in the Rare Intractable Disease management program. The incidence rate and risk of ARDs that occurred after a 1-year lag period was calculated and compared with that of control cohorts matched for age, sex, hypertension, diabetes mellitus, and dyslipidemia in a 1:10 ratio. Results: The incidence rates of ARDs in MS and NMOSD were 3.56 and 9.13 per 1000 person-years, respectively. The hazard ratios (HRs) of ARDs in MS and NMOSD were 5.35 (95% CI, 3.50 to 8.19) and 9.13 (95% CI, 5.83 to 14.28), respectively. The risk of Behçet disease (HR, 17.24; 95% CI, 4.12 to 72.14), systemic lupus erythematosus (HR, 12.25; 95% CI, 4.12 to 36.44), Sjögren syndrome (HR, 6.16; 95% CI, 1.80 to 21.04), and seropositive rheumatoid arthritis (HR, 3.32; 95% CI, 1.78 to 6.19) was increased in MS. In NMOSD, the risk of Sjögren syndrome (HR, 82.63; 95% CI, 19.00 to 359.38), systemic lupus erythematosus (HR, 30.85; 95% CI, 6.23 to 152.80), Behçet disease (HR, 15.36; 95% CI, 2.57 to 91.93), and seropositive rheumatoid arthritis (HR, 3.86; 95% CI, 1.80 to 8.31) was increased. Conclusion: The risk of ARDs was increased in MS/NMOSD, and the risk of each ARD differed between MS and NMOSD.