Endocrine Abstracts

Background: In recent years, increasing cases of congenital hypothyroidism (CH) with in situ thyroid gland (GIS) are identified. Outcome of children affected from CH with normally sited thyroid of normal size is still unknown. The objective of our study is to describe the natural history of this specific form of CH.

Methods: We retrospectively evaluated clinical, biochemical and instrumental data of 89 patients with diagnosis of CH and GIS, referred to our center after positive neonatal screening. After 3 years of age, 48 patients performed a clinical reassessment after withdrawal of levothyroxine therapy (L- T4), through biochemical evaluation with thyroid function profile (TSH, fT3, fT4), imaging evaluation with neck ultrasound and, in most cases, a scintiscan with 123-I and perchlorate discharge test. We evaluated the need for L-T4 therapy at retesting and during follow-up.

Results: In the first year of follow-up, 15 patients showed a transient CH. Among the other 74 patients, 48 performed clinical reassessment: 10 had overt hypothyroidism (20,8%), 20 showed hyperthyrotropinemia (41,7%) and 18 were euthyroid (37,5%) after L-T4 withdrawal for 4 weeks. 32 patients performed a scintiscan with 123-I and perchlorate discharge test: 6 patients presented a partial iodine organification defect, while 4 patients had a total iodine organification defect. 28 children (58,3%) resumed therapy immediately after clinical reassessment, while 20 (41,7%) suspended it. Follow-up data after retesting (median duration of 10,36 years) were available in 44 patients. Among children who had suspended therapy at retesting, 4 resumed therapy during follow-up, while in the group of children who had resumed therapy at retesting, 9 suspended it. At the end of follow-up, 22 patients (50%) were untreated and 22 (50%) were still taking L-T4 therapy. We observed no statistical differences between children who suspended or continued L-T4, in first serum TSH levels, sex ratio, or birth weight. Serum TSH at clinical reassessment showed a significant difference between two groups (P < 0,01).

Conclusions: Over a third of patients with CH and GIS had a normal thyroid function off L-T4 therapy when retested after 3 years of age. During subsequent follow-up, half of patients underwent to suspension of L-T4 therapy because of normal thyroid function. Therefore, a clinical reassessment after 3 years of age should be performed to avoid unnecessary prolonged treatment. However, it is not possible to predict whether these subjects will need therapy again, so long-term follow-up studies are needed to better understand natural history of disease.