Endocrine Abstracts

Autoimmune diseases tend to coexist in the same subjects and are more often present in women than in men. Finland has the highest incidence of type 1 diabetes (TID). However, the coexistence of autoimmune diseases and excess risk compared to individuals without T1D in unknown. This study compares the proportion of autoimmune hypothyreosis and hyperthyreosis, Addison’s disease and celiac disease in adults in Finland with and without T1D. The study included 4,758 patients with T1D from the Finnish Diabetic Nephropathy (FinnDiane) Study. For each patient with T1D, three nondiabetic control individuals, who were matched for sex, age, and place of residence in the year of diagnosis of diabetes in the FinnDiane patient, were selected from the Finnish Public Register Centre, altogether 12,710 controls. The autoimmune diseases were identified by linking the data with Finnish nationwide health registries such as the Finnish Care Register for Health Care (data available for the years 1970–2015), the Finnish National Drug Reimbursement Register (available for years 1965–2015) and the Drug Prescription Register (available for years 1993–2015). The median age of the FinnDiane patients at the end of follow-up in 2015 or at death was 51.4 (IQR 42.6–60.1) years. The most prevalent additional autoimmune disease was hypothyreosis, that was three times more common in patients with T1D compared to controls; 18.1% vs 6.0%. Hyperthyreosis was present in 2.4% of patients compared to 0.8% in controls resulting in a 2.9-times higher risk. Addison’s disease was 24 times more common in patients with T1D; 0.38% vs 0.016%. The risk of celiac disease was 4.4 times higher in the patients; 4.4% vs 0.99%. Women had higher risk of all autoimmune diseases than men, i.e. 2.5 times higher risk of hypothyreosis, 2.8 times of hyperthyreosis, 2.2 times of Addison’s disease and 1.5 times of celiac disease. 21.6% of patients with T1D had at least one additional autoimmune disease and 2.9% had two additional autoimmune diseases. Of the controls 7.3% had one, and 0.6% had two autoimmune diseases. The median age at diagnosis of hypothyreosis was lower in the patients with T1D, 41.0 (IQR 30.0–51.0) years, than in the controls, 48.0 (38.0–56.0) years (P<0.0001). This is the largest study quantifying the risk of coexisting autoimmune disease in adult individuals with T1D in Finland, the country with the highest incidence of T1D. Notably, these results highlight the importance of screening for other autoimmune diagnoses, if the patient presents with new symptoms.