ESPE Yearbook of Paediatric Endocrinology

To read the full abstract: Pediatrics. 2018;142(4). pii: e20181199.

This unique study investigated the incidence of congenital hypothyroidism from the start of the newborn screening in 1979 to 2016. The authors report a marked increase in incidence from 0.27 cases per 1000 live births in 1979–1991 to 0.41 in 1992–2004 and 0.65 in 2005–2016.

A major strength of this study is that over the complete study period, there was no change in TSH cut-offs, TSH whole blood laboratory measurement technique, or population ethnicity, which were typical confounders in previous studies [1, 2, 3]. Further, diagnostic imaging and confirmatory thyroid hormone results were available in >80% of the whole patient cohort (n=1063).

There was a stable incidence of thyroid dysgenesis (athyreosis, ectopy, hypoplasia), but a significant increase of patients with gland in situ congenital hypothyroidism. The majority of these patients with gland in situ had initial TSH values between 20–100 mU/L, thus not just borderline results, in accordance with studies from France and Italy [1, 2]. When severity was categorized by FT4 according current definitions, the significant increase was observed in cases of mild congenital hypothyroidism (FT4 10–15 pmol/L). Finally, the authors provide data on the ratio of permanent (52%) versus transient (48%) forms of congenital hypothyroidism in patients with gland in situ after standardized reevaluation. The authors point out the only weakness of the study: missing data on iodine sufficiency in the general population of Ireland. However, assuming mild iodine deficiency, one would rather expect a gradual increase of severity of disease with the highest percentage in the lowest TSH range of 8–20 mU/L.

In summary, as clinicians we need to face increasing evidence of a shift of congenital hypothyroidism phenotype away from the dysgenetic forms to a structurally and functionally milder entity, however with clear indication for substitutive treatment at birth and more than 50% even after reevaluation in this study. The cause of this shift however remains unknown, opening avenues for further research.

References: 1. Deladoëy J, Ruel J, Guiguère Y, van Vliet G. Is the incidence of congenital hypothyroidism really increasing? A 20-year retrospective population-based study in Québec. J Clin Endocrinol Metab 2011;96:2422–29.

2. Olivieri A, Fazzini C, Medda E; Italian Study Group for Congenital Hypothyroidism. Multiple factors influencing the incidence of congenital hypothyroidism detected by neonatal screening. Horm Res Paediatr 2015;83:86–93.

3. Barry Y, Bonaldi C, Goulet V, Coutant R, Léger J, Paty AC, Delmas D, Cheillan D, Roussey M. Increased incidence of congenital hypothyroidism in France from 1982 to 2012: a nationwide multicenter analysis. Ann Epidemiol 2016;26:100105.e4.