Among infants with congenital hypothyroidism (CH) and eutopic thyroid gland, clinicians should monitor demographic, clinical, and hormonal data at diagnosis and levothyroxine requirement in the first 2 years to identify those who are most likely to discontinue therapy after age 24 months, according to a study in the Journal of Clinical Medicine.

Investigators sought to determine the rate of transient CH (TCH) in all newborns diagnosed with primary CH in the Piedmont region in Italy from January 2014 to June 2019.

CH diagnosis was confirmed based on blood levels of thyroid-stimulating hormone (TSH), free thyroxine (fT4), free triiodothyronine (fT3), and thyroglobulin, and on radiological evaluation with 99Tc or121 I scintigraphy and ultrasound examination in all cases of suspected thyroid agenesis. The patients were re-evaluated at aged 2 years with prior suspension of levothyroxine for 4 weeks.


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A total of 105 newborns (57 male) were diagnosed with CH for an incidence of 1:1090. Thyroid scintigraphy showed that gland dysgenesis was present in 47.6% of newborns, and a defect in hormonogenesis with eutopic gland was observed in 52.4%. After all newborns with thyroid in situ were re-evaluated at a mean aged  2.4 years, 29/55 (52.7%) had permanent CH (PCH), and 26/55 (47.3%) had TCH.

The male/female rate was significantly higher in the PCH group compared with the TSH group (3.1 vs 0.86, P = .02). The PCH group had significantly higher TSH values (197.3±44.5 µUI/mL) vs the TCH group (55.01±7.33) (P = .009), and fT4 levels were lower among infants with PCH (6.92±0.72 vs 9.29±1.98 pg/mL, P = .03).

A serum TSH level >60 mcUI/mL had a sensitivity of 72.4% and specificity of 80.7% for PCH (likelihood ratio of 2.8). Multivariate analysis showed a higher risk for PCH (P = .001) for this cutoff as well as a higher risk of extra-thyroid malformation (P = .001). The highest specificity (100%) was for TSH levels <21.9 mcUI/L.

A 73% sensitivity and 72.4% specificity for PCH (likelihood ratio of 1.86) were observed with serum fT4 levels <7.2 pg/mL. A drug requirement >2.25 mcg/kg/d had a sensitivity of 66% and specificity of 68% for PCH (likelihood ratio of 2.1).

Study limitations include the retrospective data, and the diagnostic criteria and management of CH were different among the individual centers.

“The current data do not allow for clarification of the natural course of transient hypothyroidism in early infancy and do not indicate whether subjects with TCH need treatment with levothyroxine later in the evolutive age; therefore, long-term follow-up is required in this population,” advised the study authors.

Reference

Tuli G, Munarin J, De Sanctis L. Diagnostic re-evaluation and potential predictor factors of transient and permanent congenital hypothyroidism in eutopic thyroid gland. J Clin Med. 2021;10(23):5583. doi:10.3390/jcm10235583