Relationships between thyroid function and autoimmunity with metabolic derangement at the onset of type 1 diabetes: a cross-sectional and longitudinal study.

BACKGROUND: Type 1 diabetes (T1DM) is an autoimmune disease often associated with thyroid abnormalities. PURPOSE: We investigated the correlation between thyroid function and metabolic derangement at onset and the influence of autoimmunity on thyroid function at onset and subsequently. METHODS: We evaluated 152 patients diagnosed with T1DM between 2000 and 2012 at onset and during a mean follow-up of 5.45 ± 2.8 years. Thyroid function at onset was correlated with metabolic derangement (degree of acidosis, metabolic control and adrenal function) and compared with that of 78 healthy children. Follow-up consisted of regular evaluation of thyroid function and autoimmunity. RESULTS: Thyroid hormonal pattern was not influenced at onset by thyroid autoimmunity, but only by metabolic derangement: pH and base excess in fact were significantly lower in patients with impaired thyroid function (p < 0.0001). Patients presenting normal thyroid function at onset showed a reduced conversion from FT4 to FT3 compared to nondiabetic children (FT3/FT4 0.3 ± 0.4 in the control group, 0.24 ± 0.4 in diabetic patients, p < 0.0001). Multiple regression analysis showed the highest correlation (negative) between FT3 levels at onset and base excess (p < 0.005). Thyroid abnormalities related to metabolic derangement disappeared during follow-up. Patients with thyroid antibodies at T1DM onset were at higher risk to require levothyroxine treatment during follow-up (p < 0.05). CONCLUSIONS: Thyroid function at T1DM onset is mainly influenced by metabolic derangement, irrespective of thyroid autoimmunity. Antithyroid antibodies evaluation at T1DM onset may be helpful to define which patients are at higher risk of developing hypothyroidism.