Incidence and prevalence of thyroid dysfunction in type 1 diabetes.

AIMS: 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.

METHODS: 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.

RESULTS: 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.

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