Age‐Related Differences in Comorbidities Following Bullous Pemphigoid: A Nationwide Cohort Study

Background Bullous pemphigoid is associated with several comorbidities; however, the influence of age at diagnosis on these risks remains unclear. Objectives To examine age‐related differences in the risk of developing selected comorbidities within a nationwide cohort of patients with bullous pemphigoid. Methods We conducted a registry‐based cohort study using a pre‐existing cohort derived from the Danish National Patient Registry. Patients aged ≥ 40 years with a first‐time diagnosis of bullous pemphigoid were stratified into five age groups. Cox proportional hazards regression was used to estimate hazard ratios (HRs) with 95% confidence intervals (CIs), using patients aged 70–79 years as the reference group. Results Among patients aged 50–59 years, the risk of type 1 diabetes was significantly increased (HR 2.61, 95% CI 1.15–5.93). Patients aged 60–69 years had a higher risk of type 2 diabetes (HR 1.51, 95% CI 1.00–2.28) and malignancy (HR 1.53, 95% CI 1.11–2.12) compared with the reference group. Limitations Limitations include potential diagnostic misclassification, unmeasured confounding, including corticosteroid exposure, and limited statistical power for rare outcomes. Competing mortality was not accounted for in the analyses. Conclusions Age at diagnosis is associated with differences in comorbidity risk among patients with bullous pemphigoid. These findings support age‐stratified follow‐up, particularly with attention to diabetes in younger patients.