medwireNews: Over a third of children diagnosed with congenital hypothyroidism (CH) have discontinued treatment within 10 years of diagnosis, say French researchers who have identified predictive markers for a transient prognosis.

Yaya Barry, from Santé Publique France in Saint-Maurice, and co-workers matched data for 471 children with a eutopic thyroid gland in metropolitan France who participated in the French CH neonatal screening programme between 2006 and 2012, and had at least one reimbursement in the national health data system for L-thyroxine (LT4) therapy.

Overall, 53.5% of these patients were female, 14.2% had been born preterm and 15.9% were born small for gestational age. A quarter (24.3%) of the children had mild CH, defined as a thyroid-stimulating hormone (TSH) level below 50 mU/L, and 35.4% had a free thyroxine (FT4) concentration of at least 10 pmol/L.

After a median follow-up of 6.7 years, 32.9% of patients had discontinued LT4 therapy and were classified as having transient CH, while the remainder were considered to have a permanent condition, report Barry et al.

Multivariate analysis indicated that diagnosis of transient CH was significantly more common in children with premature birth (hazard ratio [HR]=2.1), children who had a TSH screening level below 100 mU/L (HR=3.2–7.4) and children with congenital cardiac malformations (HR=6.6). Year of birth was also a significant and positive risk factor for transient CH diagnosis. (HR=1.2 per each later year), whereas higher dose of LT4 therapy at age 12 months was associated with a reduced likelihood of transient diagnosis (HR=0.98 per 1 µg/day dose).

By contrast, transient CH was not significantly associated with sex, birthweight, first-degree familial history of thyroid disorders, and non-cardiac congenital malformations, the team reports in The Journal of Clinical Endocrinology & Metabolism.

And when the study population was extended to 484 children by inclusion of children diagnosed with Down’s syndrome, the team found that Down’s syndrome was not linked to transient CH diagnosis.

“The probability of having [transient CH] in our study population at 10 years of LT4 tracking was higher than at 5 and 3 years, suggesting a greater probability of [transient CH] over time”, observe Barry and co-authors.

And although reassessment for transient CH status became more common in patients born in 2011 and 2012 than in earlier years, the researchers emphasize that “contrary to current recommendations of the European Society for Paediatric Endocrinology Consensus guidelines, the reevaluation of thyroid function to distinguish between permanent and transient CH is probably not always performed at around 3 years of age.”

The team concludes: “Future studies are needed to explore the mechanisms underlying transient CH forms, and to estimate the role played by [transient CH] in the current increase in the incidence of CH with eutopic thyroid gland.”

By Lynda Williams

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J Clin Endocrinol Metab 2021; doi:10.1210/clinem/dgab854

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