Autoimmune thyroiditis in non-obese subjects with initial diagnosis of Type 2 diabetes mellitus

Autoimmune thyroiditis is often associated with Type 1 diabetes mellitus (T1DM). In non-obese adult-onset diabetes diagnosed initially as Type 2 diabetes mellitus (T2DM), there is a proportion of cases with so far undiagnosed T1DM. The objective of this study was to estimate the frequency of autoimmune thyroiditis (AT) among non-obese (BMI <30.0 kg/m2) patients with T2DM and to compare the frequency of AT in subgroups of patients according to the presence of glutamic acid decarboxylase antibodies (GADA), insulin requirement, and post-breakfast C-peptide levels. The study included 118 adult patients (55 men and 63 women) with the initial diagnosis of T2DM and age at the onset of diabetes > 35 yr. Median of age was 66 yr (range 39-82), and median duration of diabetes was 9 (range 1-27) yr. AT was diagnosed using thyroid peroxidase antibodies, TG-antibodies, US and TSH levels. Nineteen per cent of the subjects were found to have AT, and the frequency of AT did not significantly differ between the groups of GADA+ and GADA- subjects. There was no difference in the frequency of AT between the group treated with hypoglycemic agents and/or diet and the group requiring insulin. The frequency of AT was higher in the group with post-breakfast C-peptide levels < or = 0.8 nmol/l compared to the group with post-breakfast C-peptide levels > 0.8 nmol/l (37% vs 16%), however the group with post-breakfast C-peptide levels < or = 0.8 nmol/l had longer duration of diabetes.