Incidence and risk of developing rheumatic diseases in 19,724 patients with palindromic rheumatism in South Korea: A nationwide population-based study

Objectives: The spectrum of progression of palindromic rheumatism (PR) to chronic diseases is quite variable. Hence, this study aimed to investigate the incidence and risk of developing rheumatic diseases in PR using nationwide, population-based medical claims data from Korea. Methods: We assessed the incidence rate (IR) of PR in the population in the given year. After matching individuals with PR with those without PR (1:10) for age, gender, and the index year, we calculated the hazard ratios (HRs) with 95% confidence intervals (CIs) using the Cox proportional hazard model. Results: A total of 19,724 newly diagnosed incident PR cases were identified from 2010 to 2016. The mean age was 50.2 ± 14.9 years. The incidence of PR was 7.02 (95% CI 6.92–7.12) per 100,000 person-years (6.22 and 7.80 in men and women, respectively). During observation, 8.79% patients with PR and 0.30% individuals without PR developed various outcome diseases. Patients with PR had an increased risk of seropositive rheumatoid arthritis (HR 46.51, 95% CI [41.05–52.69]), psoriatic arthritis (44.79 [15.16–132.35]), systemic lupus erythematosus (24.53 [16.15–37.24]), mixed connective tissue disease (22.01 [7.65–63.34]), Behçet's disease (21.04 [13.81–32.06]), Sjögren's syndrome (12.36 [8.54–17.88]), ankylosing spondylitis (9.00 [6.67–12.15]), dermatomyositis/polymyositis (6.14 [2.55–14.82]), and systemic sclerosis (3.75 [1.47–9.58]) compared with individuals without PR. Conclusions: This nationwide, population-based cohort study demonstrated that about one-eleventh of patients with PR eventually develop systemic rheumatic diseases and that patients with PR have an increased risk of developing various rheumatic diseases including seropositive rheumatoid arthritis.