Incidence and prevalence of thyroid dysfunction in type 1 diabetes

To estimate prevalence and incidence of auto-immune thyroid disease and thyroid auto-antibodies in an unselected cohort of patients with DM1, including stratification by age, gender and duration of diabetes.

Patients with T1D visiting our outpatient clinic between 1995 and 2011 were included. We calculated the prevalence of AITD at first screening and estimated prevalence and incidence rates during follow-up.

A total of 1304 patients were included, 48.9% being female. Mean age of diabetes onset was 18.7 years. Of all patients without known thyroid disorder first screened for AITD, 10.3 % (n=104) was diagnosed with hypo- or hyperthyroidism. The average prevalence of AITD in our population was 112/1000 patients. We found 128 new cases of AITD, 101 cases of hypothyroidism and 27 of hyperthyroidism between 1995 and 2011 with accompanying incidences of 11.2/1000 person-years (95% CI 9.5-13.4), 8.9/1000 person-years (95% CI, 7.3-10.8) and 2.4/1000 person-years (95% CI, 1.6-3.5), respectively. Age-stratified incidence of AITD was comparable at all ages in both males and females, with an approximately two times higher incidence in females.

The incidence of AITD among T1D patients is high, but stable among all ages and independent of diabetes duration.