Prevalence of autoimmune comorbidities and association with glycemic control by CGM-derived parameters in type 1 diabetes.

Purpose: Type 1 diabetes mellitus (T1D) is a chronic autoimmune disease frequently associated with other autoimmune diseases. This study aims to evaluate the prevalence of additional autoimmunity in adults with T1D and its association with glycemic control, chronic complications, and other comorbidities.

Methods: We performed a cross-sectional study in adult patients with T1D, followed at the Endocrinology Department of a tertiary hospital, between May 2022 and May 2024. Clinical data collected included glycemic control (HbA1c and continuous glucose monitoring [CGM] parameters), diabetes complications, and other comorbidities. These parameters were compared according to the history of autoimmune diseases. Statistical analysis was performed using parametric and non-parametric tests, ANCOVA and logistic regression models, unadjusted and adjusted for age and sex.

Results: Of the 439 participants (48.8% female and mean age 36.8 ± 14.1 years), 33.8% had at least one autoimmune disease, predominantly Hashimoto's thyroiditis (28.8%) and celiac disease (3.9%), with higher prevalence in women (p < 0.001). HbA1c (7.7 ± 1.3 vs. 7.8 ± 1.4%, p = 0.53) and CGM-derived parameters, such as glucose management indicator (7.4 ± 0.9 vs. 7.4 ± 0.8%, p = 0.44) and time in range (58.7 ± 18.9 vs. 56.6 ± 16.5%, p = 0.84), were similar in patients with and without autoimmune diseases.

Conclusions: Over one fourth of patients with T1D had a concomitant autoimmune disease. Our results suggest that the presence of other autoimmune diseases may not preclude the attainment of similar glycemic targets. Given the high risk of autoimmunity in T1D, systematic screening and personalized treatment should be considered. Prospective studies are warranted to explore the long-term implications on metabolic control and cardiovascular outcomes.