Comorbidity in Lichen Planus: A Retrospective Population-Based Case–Control Study in Sweden

Lichen planus (LP) is a chronic immune-mediated inflammatory disease of unknown etiology affecting the skin and mucous membranes and is frequently associated with comorbid conditions, although data from Swedish populations remain limited. This retrospective population-based case–control study included all registered citizens in Region Jönköping, Sweden, between 2013 and 2022, to examine comorbidities, estimate prevalence and incidence, assess diagnostic validity of ICD-10 coding (L43), and evaluate treatment patterns. Incidence and prevalence were calculated, demographic and treatment characteristics were described, and diagnostic validity was assessed through independent medical record review of 70 randomly selected cases to determine positive predictive value (PPV). Associations between LP and predefined comorbidities were analyzed using binomial logistic regression adjusted for age and sex. Among 361,812 individuals, prevalence was 235.5 and incidence 19.6 per 100,000 inhabitants. The PPV of the LP diagnosis was 78.6%, yielding an adjusted prevalence of 184.9 per 100,000 inhabitants. Over one third of prevalent patients received topical therapy, primarily corticosteroids. LP was significantly associated with thyroid, malignant, metabolic, and autoimmune conditions. LP is relatively uncommon, ICD-10 coding shows acceptable validity, and its association with clinically relevant comorbidities highlights the need for comprehensive patient assessment.