Congenital hypothyroidism

There are three types of TH deficiency known to impact fetal development, including (Figure 108.1) isolated fetal hypothyroidism (congenital hypothyroidism CH), combined maternal and fetal hypothyroidism (endemic cretinism EC), and isolated maternal hypothyroidism (primary maternal hypothyroidism). According to the review of CH (American Academy of Pediatrics, 2006), TH deficiency originates from birth and is mainly due to the failure of... 

My comment is in response to Dr. Laurberg s comment. There is an important difference between a hypothyroid child bom in an iodine deficient area and congenital hypothyroidism. Congenital hypothyroid children probably develop normally after birth, when given adequate thyroxine treatment, because their brain was selectively protected by maternal T4 until birth. On the contrary, in severely iodine deficient areas, the fetal brain cannot benefit from the same protection because of the low thyroxine levels in maternal serum. 

Use of measurement of blood thyroxine or thyroid-stimulating hormone (TSH) in the neonatal diagnosis of congenital hypothyroidism. 

Figure 42-11. Model of iodide metabolism in the thyroid follicle. A follicular cell is shown facing the follicular lumen (top) and the extracellular space (at bottom). Iodide enters the thyroid primarily through a transporter (bottom left). Thyroid hormone synthesis occurs in the follicular space through a series of reactions, many of which are peroxidase-mediated. Thyroid hormones, stored in the colloid in the follicular space, are released from thyroglobulin by hydrolysis inside the thyroid cell. (Tgb, thyroglobulin MIT, monoiodotyrosine DIT, diiodotyro-sine Tj, triiodothyronine T4, tetraiodothyronine.) Asterisks indicate steps or processes that are inherited enzyme deficiencies which cause congenital goiter and often result in hypothyroidism.

Congenital hypothyroidism is still seen in the United States, and all newborns in the United States undergo screening with a TSH level. As soon as the hypothyroid state is identified, the newborn should receive the full LT4 replacement dose. The replacement dose of LT4 in children is age-dependent. In newborns, the usual dose is 10 to 17 mcg/kg per day. LT4 tablets may be crushed and mixed with breast milk or formula. Serum FT4 levels (target 1.6-2.2 ng/dL or 20.59-28.31 pmol/L) are used for dose titration in infants because the TSH level may not respond to treatment as it does in older children and adults. By 6 months of age, the required dose is reduced to 5 to 7 mcg/kg per day, and from ages 1 to 10 years, the dose is 3 to 6 mcg/kg per day. After age 12, adult doses can be given. 

Hypothyroidism commonly occurs months to years after RAI. The acute, short-term side effects include mild thyroidal tenderness and dysphagia. Long-term follow-up has not revealed an increased risk for development of thyroid carcinoma, leukemia, or congenital defects. 

Newborn screening is used just after birth to identify genetic disorders that can be treated early in life. Millions of babies are tested each year in the United States. All states currently test infants for phenylketonuria (a genetic disorder that causes mental retardation if left untreated) and congenital hypothyroidism (a disorder of the thyroid gland). Most states also test for other genetic disorders. 

Children - Follow the recommendations in the following table. In infants with congenital or acquired hypothyroidism, institute therapy with full doses as soon as diagnosis is made. 

Congenital hypothyroidism - Siarimg dose is 5 mcg/day, with a 5 meg increment every 3 to 4 days until the desired response is achieved. Infants a few months old may require only 20 mcg/day for maintenance. At 1 year of age, 50 mcg/day may be required. Above 3 years, full adult dosage may be necessary. 

Children - In infants with congenital hypothyroidism, institute therapy with full... 

Congenital hypothyroidism - The incidence of congenital hypothyroidism is relatively high (1 4000). Routine determinations of serum T4 and/or TSH are... 

Kallen and Robert (2000) found no adverse effects on congenital malformations, childhood cancer, infant mortality, low Apgar score, neonatal jaundice, or neonatal hypothyroidism among infants and children who lived in areas where drinking water was disinfected with chlorine dioxide, compared to controls living in... 

Early worries about risk of cancer or leukaemia have proven unfounded in prolonged follow-up studies. However radioactive treatment is contraindicated in pregnant woman or nursing mothers. Other risks for the fetus are abortion, intrauterine death, congenital malformation and congenital hypothyroidism (if administered after 12 weeks gestation). It is customary to avoid pregnancy for the first... 

Melvin GR, Aceto T Jr, Barlow J, Munson D, Wierda D. Iatrogenic congenital goiter and hypothyroidism with respiratory distress in a newborn. S D J Med 1978 31(10) 15-19. 

Maayan-Metzger A, Sack J, Mazkereth R, Vardi A, Kuint J. Somatostatin treatment of congenital chylothorax may induce transient hypothyroidism in newborns. Acta Paediatr 2005 94 785-9. 

There has been a retrospective study of the frequency of amiodarone-associated thyroid dysfunction in adults with congenital heart disease (41). Of 92 patients who had taken amiodarone for at least 6 months (mean age 35, range 18-60 years), 36% developed thyroid dysfunction— 19 became hyperthyroid and 14 hypothyroid. The mean dosage was 194 (100-300) mg/day, and the median duration of therapy was 3 (0.5-15) years. Female sex (OR = 3) and unoperated or palliated cyanotic congenital heart disease (OR = 7) were significant susceptibility factors for thyroid dysfunction. The risk was also dose-related. Although the authors conceded that they may have over-estimated the... 

De Wolf D, De Schepper J, Verhaaren H, Deneyer M, Smitz J, Sacre-Smits L. Congenital hypothyroid goiter and amiodarone. Acta Paediatr Scand 1988 77(4) 616-8. 

There are many forms of hypothyroidism, differing in their cause and age of onset (see Table 31-1). Severe adult hypothyroidism (myxedema) may occur idio-pathically or may be caused by specific factors such as autoimmune lymphocytic destruction (Hashimoto disease). In the child, thyroid function may be congenitally impaired, and cretinism will result if this condition is untreated. Hypothyroidism may result at any age if the dietary intake of iodine is extremely low. Several other forms of hypothyroidism that have a genetic or familial basis also exist.54... 

LaFranchi S. Congenital hypothyroidism Etiologies, diagnosis, and management. Thyroid. 199 9 735. 

Kelsh MA, Buffler PA, Daaboul JJ, Rutherford GW, Lau EC, Barnard JC, Exuzides AK, Madl AK, Palmer LG, Lorey FW (2003) Primary congenital hypothyroidism, newborn thyroid function, and environmental perchlorate exposure among residents of a Southern California community. J Occup Environ Med, 45 1116-1127. 

Lamm SH Doemland M (1999) Has perchlorate in drinking water increased the rate of congenital hypothyroidism J Occup Environ Med, 41 409-411. 

K3. Kato, N., Ishii, S., Naruse, H., Irie, M., Arakawa, H., and Tsuji, A., Enzyme immunoassay of thyroid-stimulating hormone using dried blood samples. A simple technique of screening for congenital hypothyroidism. Anal. Lett. 13, 1555-1565 (1980). 

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