Congenital hypothyroidism in children with eutopic gland or thyroid hemiagenesis: prognostic factors for transient vs. permanent hypothyroidism.

Objectives: More than one third of children with congenital hypothyroidism (CH) and thyroid gland  (or eutopic gland) have transient hypothyroidism. It remains difficult to determine early on whether hypothyroidism will be transient which may cause overtreatment and its complications in these children. Our primary aim was to determine prognostic factors for transient hypothyroidism in children with congenital hypothyroidism and eutopic gland or thyroid hemiagenesis.

Methods: We retrospectively reviewed medical records of 111 children, born between 1996 and 2017, diagnosed with congenital hypothyroidism and eutopic gland or hemiagenesis and treated at the Nancy Regional and University Hospital.

Results: Fifty four infants (48.6%) had permanent congenital hypothyroidism (PCH) and 57 (51.4%) transient congenital hypothyroidism (TCH). Prognostic factors for TCH included prematurity, twin pregnancy, low birth weight and Apgar score <7, while low FT3 at diagnosis, maternal levothyroxine treatment, a family history of thyroid dysfunction and TSH ≥10 mUI/L while receiving treatment were associated with PCH. Knee epiphyses on X-ray at diagnosis were absent only in children with PCH. The median levothyroxine dose during follow-up was significantly lower in the TCH group compared to the PCH group. A levothyroxine dose of ≤3.95, ≤2.56, ≤2.19 and ≤2.12 μg/kg/day at 6 months, 1, 2 and 3 years of follow-up, respectively, had the best sensitivity-to-specificity ratio for predicting TCH.

Conclusions: Even though it remains difficult to predict the course of hypothyroidism at diagnosis, we were able to identify several prognostic factors for TCH including perinatal problems and lower levothyroxine requirements that can guide the physician on the evolution of hypothyroidism. Clinical Trial Registration Number: NCT04712760.