Effects of iodine supplementation on thyroid function in children with mild congenital hypothyroidism and non-autoimmune subclinical hypothyroidism.

Abstract

Purpose: The role of iodine treatment in congenital and acquired non-autoimmune subclinical hypothyroidism (SH) remains unclear, although it has been demonstrated that iodine can improve thyroid function in some dyshormonogenetic defects. We aimed to evaluate the effect of iodine administration in children with congenital hypothyroidism (CH) with gland in situ (GIS) and non-autoimmune SH diagnosed during childhood.

Patients and methods: 13 children with CH and GIS and 19 with non-autoimmune SH (7 females, 25 males; median age 10 years) were given iodine for 9 months at increasing doses from 50 µg/day to 150 µg/day, after stopping levothyroxine (LT4), when taken. 4 children had DUOX2 mutations, whereas the etiology was unknown in the remaining cases. Thyroid hormones, anti-thyroid antibodies and ultrasound were evaluated every 3 months for 12 months and then after 1 year.

Results: At increasing of the daily iodine dose, there was in both groups a slight progressive increase in TSH, that became statistically significant only after 150 µg/day, both in the SH group (p 0.044) and in the whole group (p 0.015). The other parameters did not change with treatment. No children developed thyroid autoimmunity, even one year after iodine withdrawal, and iodine treatment did not modify the course of disease as shown by follow-up data.

Conclusion: This study shows a failure of physiological doses of iodine to improve mild CH with GIS and idiopathic SH. The increase of serum TSH during treatment may reflect the spontaneous course of the disease in children rather than a detrimental effect of iodine.