The severity of congenital hypothyroidism of central origin should not be underestimated.

CONTEXT: Congenital hypothyroidism (CH) may be of thyroidal (CHT) or central origin (CHC). Worldwide, most neonatal screening programs are TSH-based and effectively detect CHT. Only a few screening programs measure total or free T4 and TSH simultaneously or stepwise, enabling detection of CHT as well as CHC. A frequently used argument against screening for CHC is its presumed mild hypothyroid character. In the recently published European Society for Paediatric Endocrinology (ESPE) CH consensus guidelines on screening, diagnosis, and management, severity of CH is classified based on initial free T4 (FT4) concentrations.

OBJECTIVE: Our objective was to assess disease severity of CHC compared with CHT in a Dutch cohort of CH patients.

METHODS: Pretreatment FT4 concentrations were analyzed in all children with CH detected by the Dutch neonatal T4+TSH+T4-binding-globulin (TBG) screening between 1995 and 2011. Disease severity was classified using the FT4-based ESPE classification.

RESULTS: Between 1995 and 2011, 1288 children were diagnosed with CH. Data of 1200 (143 CHC and 1057 CHT) were available for analysis. Based on FT4 concentrations, 4 children with CHC (2.8%) had severe, 75 (52.4%) moderate, and 64 (44.8%) mild CH. In the CHT group, 280 children (26.5%) had severe, 341 (32.3%) moderate, and 436 (41.2%) mild CH.

CONCLUSION: Our results indicate that, based on initial FT4 values, severe CH was much more prevalent in CHT compared with CHC. However, CHC itself should not be considered as only mild because more than half of CHC patients have moderate CH with initial FT4 below 10 pmol/L (0.78 ng/dl).