Importance of thyroglobulin levels for diagnosis and monitoring of follicular thyroid carcinoma in an adolescent with severe iodine deficiency.

Optimal management of differentiated thyroid cancer in childhood is undetermined. During monitoring of thyroid carcinoma, serum thyroglobulin (hTG) levels provide valuable information. hTG levels not only increase in differentiated thyroid cancers but also in iodine deficiency because of compensation by the thyroid gland. A 14.6 year-old girl was diagnosed with nodular goiter, subclinical hypothyroidism and severe iodine deficiency. She had a very high hTG level. Despite benign fine-needle aspiration biopsy (FNAB), because the hTG level was still very high after treatment with LT4, thyroidectomy was undergone. Cytopathological examination showed minimally invasive follicular thyroid carcinoma. During follow-up, to exclude the presence of persistent/recurrent disease, the hTG level rose to an undesirably high level after withdrawal of TSH suppressive therapy, and radioiodine ablation therapy was applied. This report shows that even if there is an explanation for nodular goiter and high hTG levels, such as iodine deficiency, malignancy cannot be ruled out without thyroidectomy. FNAB is not reliable especially in iodine deficient areas. Serum hTG measurement is a valuable tool for both diagnosis and follow-up of differentiated thyroid carcinoma in children.