Summary

The association between Down syndrome (DS) and autoimmune endocrinopathies is well established. These disorders become increasingly frequent as children grow older and the onset of one often predisposes to the development of others. However, there are few cases in the literature reporting the simultaneous onset of type 1 diabetes mellitus and hyperthyroidism in children with DS. We describe a case of an 8-year-old girl with DS who presented at the emergency department with hyperglycaemia and ketosis as a primary manifestation of type 1 diabetes mellitus. During the initial investigation, hyperthyroidism was detected, with thyroid-stimulating hormone<0.01 µUI/mL, positive antithyroid antibodies and an increase in thyroid gland on ultrasound. The authors present this case to underline the usefulness of monitoring thyroid function at the diagnosis of diabetes, even without apparent clinical manifestations, and to alert for the possibility of autoimmune endocrine dysfunction in children with DS.