Diagnosing and treating congenital hypothyroidism

Along with newborn screening (NBS), treatment for congenital hypothyroidism (CH) requires timely diagnosis, accurate thyroid function testing results, effective treatment, and consistent follow-up, according to a recent review.

CH is a common source of intellectual disability worldwide. It presents through insufficient thyroid hormone (TH) levels for proper body tissue development and function. CH is often permanent, with clinical and laboratory follow-up vital for management.

After NBS, levothyroxine (L-T4) therapy can help prevent intellectual disabilities, psychomotor dysfunction, and impaired growth in children. As data defining CH and discussing long-term results of treatment is inconsistent, researchers reviewed past practices and future directions, along with providing evidence for CH management.

Thyroid gland dysfunction is the most common cause of CH. This includes thyroid dysgenesis, dyshormonogenesis, and impairment of neonatal thyroid function from extrinsic factors such as maternal antithyroid medications. 

TH plays a key role in development of fetal tissues, including the nervous system. Around the third week of gestation, the fetal thyroid begins to form, with TH synthesized around weeks 10 to 12 of gestation. 

The fetus relies on maternal thyroxine (T4) prior to TH synthesis, with T4 one-third to one-half of normal levels in infants unable to synthesize T4. Combined maternal and fetal hypothyroidism could lead to severe neurodevelopmental impairment, highlighting the need for timely prenatal care before and during pregnancy involving the detection and management of maternal thyroid disease.

Iodine deficiency is a common source of intellectual disability worldwide, as iodine is vital for TH production. Iodine supplementation before and during pregnancy is recommended for treating iodine deficiency, with universal salt iodization recommended by the World Health Organization and United Nations Children’s Fund.

Screening newborns is an effective method of detecting CH. State or provincial public health laboratories perform cost-effective NBS within their geological areas. This process involves obtaining a dried blood spot which is transferred to a laboratory for testing. 

The recommended age of newborns for NBS is 48 to 72 hours, which leads to difficulties when infants are discharged early. It is best for infants to be screened within the recommended timeframe, but prior to transfusion of blood products. Communication is also necessary when transferring infants between hospitals to avoid missing collection of the NBS specimen.

After screening confirms CH, treatment includes L-T4 at a starting dose of 10 to 15 mcg/kg per day, given in a single dose. While children with severe CH may need a brand name L-T4 formulation, genetic tablets are often enough for afflicted children.

L-T4 treatment is administered with the goals of normal growth and neurocognitive development. Early initiation and adequate treatment are major factors in the success of L-T4. Later detection, inadequate doses, and more severe CH can all present obstacles in reaching the goals of L-T4 treatment.

There is still little evidence on the effects of overtreatment of L-T4, and the recommended dose could change over time. Close laboratory monitoring can help maintain TH levels in the proper range. Additionally, follow-up is often necessary to avoid negative consequences for development.

Evidence has shown the success of NBS, but investigators recommended that physicians consider hypothyroidism even in cases of normal test results. Regardless of NBS results, if signs of CH appear in an infant, actions should be taken to prevent neurodevelopmental impairment.

Reference

Rose SR, Wassner AJ, Wintergerst KA, Yaya-Jones N, Hopkin RJ, Chuang J. Congenital hypothyroidism: screening and management. Pediatrics. 2022;151(1). doi:10.1542/peds.2022-060420