(10) Incidence of Autoimmune Disorders among Patients with Atopic Dermatitis in the US

Background: Atopic dermatitis (AD) is an inflammatory skin disorder affecting approximately 15 - 20% of children and 1-3% of adults worldwide. Prior studies have examined associations between AD and incident autoimmune diseases (IADs) with mixed results. These conflicting findings may be due to the use of unvalidated outcome algorithms. We examined similar associations between AD and select IADs using validated algorithms.

Objective: To assess the association between AD and the risk of new-onset IADs.

Methods: We conducted a population-based cohort study using the Optum Clinformatics US health insurance claims database. The incidence rates (IRs) of four IADs were compared among patients with and without AD between January 1, 2016 and March 1, 2020. AD was defined as ≥2 International Classification of Diseases version 10 (ICD-10) AD diagnoses (L20.0, L20.81, L20.82, L20.84, L20.89, L20.9) at least 30 days apart, and in a secondary analysis, severe AD was defined as any evidence of systemic corticosteroids, azathioprine, cyclosporine A, methotrexate, mycophenolate mofetil, interferon gamma, intravenous immunoglobulin, or phototherapy use in the 365 days prior to and including the index date. The outcomes were autoimmune hepatitis (AIH), inflammatory bowel disease (IBD), rheumatoid arthritis (RA), and systemic lupus erythematosus (SLE), identified using validated algorithms with positive predictive values ≥ 0.83 based on ICD-10 codes.  We used Poisson regression with cohorts matched 1:1 on age, sex, race, and calendar year to estimate incidence rates and incident rate ratios (IRRs) with 95% confidence intervals (95% CI).

Results: We included a total of 149,820 patients. The adjusted IRs per 100,000 person-years among patients with and without AD were 12.71 (95% CI 7.38, 21.89) and 11.95 (95% CI 6.22, 22.97) respectively for AIH, 32.54 (95% CI 23.13, 45.77) and 13.39 (95% CI 7.2, 24.88) for IBD, 175.97 (95% CI 151.99, 203.74) and 115.58 (95% CI 93.67,142.61) for RA, and 9.55 (95% CI 4.97,18.35) and 4.33 (95% CI 1.4, 13.43) for SLE. The corresponding IRRs of AIH, IBD, RA, and SLE were 1.06 (95% CI 0.45,2.49), 2.43 (95% CI 1.2,4.93), 1.52 (95% CI 1.18,1.97), and 2.2 (95% CI 0.6,8.14) respectively. When the analyses were restricted to patients with severe AD, compared to patients without AD, the IRRs increased to 3.36 (95% CI 1.19, 9.43), 4.58 (95% CI 1.86, 11.28), 5.02 (95% CI 3.73, 6.77) for AIH, IBD, and RA respectively, but decreased to 1.79 (95% CI 0.19, 17.16) for SLE.

Conclusion:   Patients with AD, compared to patients without AD had a higher incidence of IBD and RA. Patients with severe AD, compared to patients without AD had a higher incidence of AIH, IBD, and RA respectively. Results suggest there may be a difference in the incidence of SLE in patients with and without AD, but further research is needed.