Thyroid function tests of iodine deficiency goiter can mimic thyroid hormone resistance alpha.

Objectives: Iodine deficiency goiter can develop in children on a restrictive diet and most have normal thyroid function. We report a 6-year-old girl with iodine deficiency goiter with thyroid function studies mimicking thyroid hormone resistance alpha. Thyroid hormones mediate its effects through thyroid hormone receptors alpha and beta. Biochemical picture of low/low-normal T4 and high/high-normal T3 levels, variably reduced reverse T3 and normal TSH is characteristic of thyroid hormone resistance alpha.

Case Presentation: A 6-year-old girl, born out of non-consanguineous marriage presented with goiter of 1.5 years duration. She was without symptoms of thyroid dysfunction. The patient was evaluated at one year of age for macrocephaly with cranial ultrasound which was normal. She had normal growth and development. Patient was vegan and was not on any medications or supplements. Laboratory work up showed TSH 5.03 uIU/mL (0.34-5.5), FT4 0.3 ng/dL (0.58-1.2), FT3 5.3 pg/mL (2.5-3.9), total T3 258 ng/dL (94-241), reverse T3 <5.0 ng/dL (8.3-22.9) and negative thyroglobulin antibody and thyroid peroxidase antibody. Thyroglobulin level was 1,098.8 ng/mL (<13 ug/L), and urine iodine 15.8 ug/L (<100 ug/L) confirming a diagnosis of iodine deficiency goiter. Patient was started on iodine supplements, 150 ug daily and repeat work up 3 months later were TSH: 2.717 uIU/mL, T3, total 182 ng/dL, T4, total 9.3 ug/dL, FT 4 2.1 ng/dL.

Conclusions: Iodine deficiency goiter may present with low FT 4, elevated T3 and normal TSH mimicking thyroid hormone resistance alpha and should be considered in children on restrictive diet.