Prevalence and Incidence of idiopathic Inflammatory Myopathies in Korea: a Nationwide Population-based Study over 10 years

Yoon-Kyoung Sung¹, Hyoungyoung Kim¹, Jisun Myung², Eunwoo Nam², Sun-young Jung³, Eun Jin Jang⁴, Dae-Hyun Yoo¹, Soo-Kyung Cho¹

1. Department of Rheumatology, Hanyang University Hospital for Rheumatic Diseases, Seoul, Republic of Korea

2. Biostatistical Consulting and Research Lab, Medical Research Collaborating Center, Hanyang University, Seoul, Republic of Korea

3. College of Pharmacy, Chung-Ang University, Seoul, Republic of Korea

4. Department of Information Statistics, Andong National University, Andong, Republic of Korea

Background/Purpose: Idiopathic inflammatory myopathies (IIMs) are rare rheumatic diseases, and their incidence vary greatly across studies The aims of this study were to estimate the prevalence and incidence of IIMs in Korea from 2006 to 2016.

Methods: Using data from the Korean National Health Insurance Service (NHIS) between 2004 and 2016, patients with IIMs were identified based on the diagnostic codes including juvenile dermatomyositis (JDM) of M330, dermatomyositis (DM) of M331 or M339, polymyositis (PM) of M332 and registration code of Individual Copayment Beneficiaries Program (ICBP) for rare and intractable disease. The incident cases were captured for patients with an IIM diagnostic code & ICBP code for at least 1 physician visit with a disease-free period for 24 months before the index date.

Results: In Korea, a total of 1,150 patients with IIMs (117 JDM, 521 DM, 512 PM) were observed in 2006, and the number of IIM patients was increased to 2,281 (122 JDM, 1211 DM, 948 PM) by 2016. Considering that the total population of Korea is about 50 million, the prevalence was estimated at 2.3-4.4 (1.0-1.2 for JDM, 1.4-2.9 for DM, 1.4-2.3 for PM) /100,000 PY. We identified 218 incident cases of IIM in 2006 (18 JDM, 98 DM, 102 PM) and 237 patients (9 JDM, 114 DM, 114 PM) in 2016, respectively. The incidence rate was estimated at 2.9-4.9 (0.7-1.8 for JDM, 1.8-3.1 for DM, 1.6-3.0 for PM) /1,000,000 PY between 2006 and 2016 and it did not reveal any tendency of variation over 10 years. The mean age (¡¾standard deviation) of incident patients with IIM was 54.8 (¡¾17.2) years and the percentage of females was 62.8%. Incidence increased with age and peaked among those aged 51-60 years of age.

Conclusion: We report the prevalence and incidence of IIMs in Korea at the nationwide population level. Although the prevalence seems to be increasing recently, the incidence did not reveal any tendency of variation over 10 years.