Type 1 Diabetes/Hidradenitis Suppurativa Comorbidity—A Population-Based Study

<b>Background</b>: Type 1 diabetes (T1D) and hidradenitis suppurativa (HS) share several metabolic and inflammatory dysfunctions. Prior studies of the potential link between the diseases either lacked validated T1D diagnoses or established only an indirect association. This study sought to determine the odds of HS developing in patients with a validated diagnosis of T1D and to characterize the clinical features of HS/T1D comorbidity. <b>Methods</b>: A population-based nested case-control study was conducted including patients with HS and controls matched 5:1 for age, sex, and primary care clinic. T1D was diagnosed using a specialized algorithm, achieving 90% accuracy. Diagnostic validity was confirmed by diabetes specialists who manually reviewed a random subset of the files. Unadjusted and adjusted odds ratios (OR/aOR) were calculated to determine the odds of incident HS in patients with T1D. <b>Results</b>: The study included 10,919 patients with HS and 53,314 controls. A history of T1D was associated with an elevated odds of new-onset HS (OR 1.80 95% CI (1.30-2.40), <i>p</i> < 0.001), even after adjusting for demographics and metabolic and autoimmune comorbidities (aORs > 1.7, <i>p</i> < 0.001). Patients with HS/T1D comorbidity had higher proportions of autoimmune conditions than patients with HS alone (<i>p</i> < 0.001) and a higher mean Charlson Comorbidity Index score than both patients with HS alone (3.5 vs. 0.9, <i>p</i> < 0.001) and T1D alone (3.5 vs. 2.2, <i>p</i> = 0.004). <b>Conclusions</b>: T1D is associated with higher odds of the subsequent development of HS. Awareness of HS/T1D comorbidity is recommended owing to the elevated burden of metabolic and autoimmune conditions.