Incidence of cutaneous lupus erythematosus and systemic progression: A Nationwide study in Korea

BACKGROUND: Cutaneous lupus erythematosus (CLE) is an LE-specific cutaneous manifestation that can occur in isolation or with systemic lupus erythematosus (SLE). Estimates of CLE incidence, skin cancer burden and progression to SLE in Asian populations are limited. OBJECTIVE: To investigate the nationwide incidence of CLE in Korea, its association with premalignant and malignant skin lesions and the risk of progression to SLE. METHODS: This population-based study used the Korean National Health Insurance Service-National Health Information Database (2005-2020). CLE was identified using ICD-10 code L93; cases with SLE were included, whereas cases without SLE required ancillary testing or prescriptions. CLE and SLE diagnoses within 6 months were considered concurrent. Progression to SLE was assessed using time-to-event analyses and cumulative incidence estimates. RESULTS: Overall, 32,337 patients with CLE were identified [mean (SD) age, 42.9 (17.4) years; 23,436 (72.5%) female], and 5367 (16.6%) had concomitant SLE. Discoid lupus erythematosus (DLE) was the most common subtype (22,463 [69.5%]), followed by other localized LE (8594 [26.6%]) and subacute cutaneous lupus erythematosus (SCLE) (3465 [10.7%]). Mean annual CLE incidence was 3.98 per 100,000 person-years (95% CI, 3.94-4.03), with a modest upward trend (p for trend = 0.014). CLE was associated with higher risks of actinic keratosis and cutaneous malignancies, most pronounced within the first 2 years but remaining significant during follow-up. A total of 563 patients (2.0%) developed SLE after CLE diagnosis, and the mean (SD) time to progression was 3.2 (3.0) years. Overall 5-year cumulative incidence of progression to SLE was 11.4%, higher in SCLE than DLE (20.8% vs. 9.5%). CONCLUSIONS: CLE incidence in Korea was comparable to prior population-based estimates, and CLE was associated with a higher risk of premalignant and malignant skin lesions. Considering progression from CLE to SLE clustered within the first 5 years after CLE diagnosis, risk-stratified evaluation during this period may be warranted.