General Information, Symptoms, Causes, Rates of Incidence, Screening, Treatments, and Prognosis of Congenital Hypothyroidism
There’s all kinds of information out there about hypothyroidism. Part of the reason I wanted to start this blog is because I have not found much information regarding permanent congenital hypothyroidism. In fact, “anathyroidism” seems more appropriate a term due to it not being there at all, but as I understand it, “anathyroidism” isn’t actually a word.
Many children who are born with hypothyroidism grow out of it or at least improve over time, so a lot of the research on hypothyroidism deals with that rather than a permanent condition. I found a wonderful open-access article from the Orphanet Journal of Rare Diseases. It’s quite long and pretty dry, so below are excerpts of the most relevant information. You can read the entire article here, if you are interested in learning more.
[My comments and tips will be bracketed like so].
General Description of Congenital Hypothyroidism
“Congenital hypothyroidism (CH) occurs in approximately 1:2,000 to 1:4,000 newborns. The clinical manifestations are often subtle or not present at birth. This likely is due to trans-placental passage of some maternal thyroid hormone, while many infants have some thyroid production of their own. Common symptoms include decreased activity and increased sleep, feeding difficulty, constipation, and prolonged jaundice. On examination, common signs include myxedematous facies [puffy face with dark circles under eyes], large fontanels [soft spot on head], macroglossia [thick tongue], a distended abdomen with umbilical hernia, and hypotonia [decreased muscle tone]. “Congenital hypothyroidism (CH) is defined as thyroid hormone deficiency present at birth. Thyroid hormone deficiency at birth is most commonly caused by a problem with thyroid gland development (dysgenesis) or a disorder of thyroid hormone biosynthesis (dyshormonogenesis). These disorders result in primary hypothyroidism. Secondary or central hypothyroidism at birth results from a deficiency of thyroid stimulating hormone (TSH).” “Congenital hypothyroidism is classified into permanent and transient CH. Permanent CH refers to a persistent deficiency of thyroid hormone that requires life-long treatment. Transient CH refers to a temporary deficiency of thyroid hormone, discovered at birth, but then recovering to normal thyroid hormone production. Recovery to euthyroidism typically occurs in the first few months or years of life.”
Incidence Rates
“Prior to the onset of newborn screening programs, the incidence of congenital hypothyroidism, as diagnosed after clinical manifestations, was in the range of 1;7,000 to 1:10,000. With the advent of screening of newborn populations, the incidence was initially reported to be in the range of 1:3,000 to 1:4,000. With more experience from state, regional, and national screening programs, it has become apparent that the incidence varies by geographic location. A report from the French newborn screening program summarizing a 20 year period found the incidence of permanent hypothyroidism to be 1:10,000, whereas a report from the Greek Cypriot population over an 11 year period found the incidence in newborns to be 1:800.” “In addition, there is some variation in the incidence among different racial and ethnic groups, and the mix of these groups has changed. Several U.S. programs have reported a higher incidence in the Asian, Native American, and Hispanic populations and lower in the American Black population as compared to the White population… A summary of the New York State program during the years 2000 to 2003… found the incidence nearly double in twin births (1:876) as compared to singletons (1:1765), and even higher with multiple births (1:575). Older mothers (> 39 years) had a higher incidence (1:1,328) compared to younger mothers (< 20 years, 1:1,703)… Nearly all screening programs report a female preponderance, approaching 2:1 female to male ratio.”
Congenital Hypothyroidism Symptoms
“Symptoms of congenital hypothyroidism are initially nondescript; however, the maternal and pregnancy history may provide some clues. In twenty percent, gestation extends beyond forty-two weeks . One may also find evidence of maternal autoimmune thyroid disease or an iodine deficient diet… Once home, these babies are quiet and may sleep through the night. Additional symptoms include a hoarse cry and constipation.” “Up to one third have a birth weight greater than the ninetieth percentile. On initial examination, the most common signs are umbilical hernia, macroglossia and cold or mottled skin. Thyroid hormone is also important in the formation and maturation of bone. This can lead to a wide posterior fontanel of greater than 5 mm. This, along with persistent jaundice and poor feeding are the most striking clinical features.” “Congenital hypothyroidism appears to be associated with an increased risk of congenital malformations… Of these, the majority were cardiac. Other associated malformations include spiky hair, cleft palate, neurologic abnormalities and genitourinary [urinary tract] malformations. Also, the incidence of congenital hypothyroidism is increased in patients with Down’s Syndrome.”
Congenital Hypothyroidism Causes
“Permanent congenital hypothyroidism may be due to primary or secondary (central) causes. Primary causes include defects of thyroid gland development, deficiencies in thyroid hormone production, and hypothyroidism resulting from defects of TSH binding or signal transduction. Peripheral hypothyroidism results from defects in thyroid hormone transport, metabolism, or resistance to thyroid hormone action. Secondary or central causes include defects of thyrotropin releasing hormone (TRH) formation or binding and TSH production.” “In iodine sufficient countries, 85% of congenital hypothyroidism is due to thyroid dysgenesis… Thyroid dysgenesis presents in three major forms: thyroid ectopy, athyreosis and thyroid hypoplasia [incomplete development]. Thyroid ectopy refers to an ectopic location of the thyroid gland. This accounts for two-thirds of congenital hypothyroidism due to thyroid dysgenesis and is twice as common in females. In these cases, a thyroid remnant is usually found along the normal pathway of the thyroglossal duct. This represents the path taken by the developing thyroid as it descends from the base of the tongue to its final location in the neck… Athyreosis refers to the complete absence of thyroid tissue. Athyreosis and thyroid hypoplasia account for the remaining one third of thyroid dysgenesis.” “Thyroid dysgenesis is generally thought to be sporadic in occurrence. However, recent evidence points to the possibility of a genetic component. One study of all cases of thyroid dysgenesis found that 2% were familial in occurrence. Additional studies also showed that 7.9% of first degree relatives of infants with congenital hypothyroidism had a thyroid developmental anomaly.”
Congenital Hypothyroidism Screening for Infants
“The specimen used for newborn screening tests is blood from a heel-prick collected on special filter paper cards. The specimen is routinely collected between two and five days of age (or at discharge from the hospital, if this occurs earlier); some programs use [umbilical] cord blood for screening. In addition, some programs also routinely obtain a 2nd specimen between two and six weeks of age.” “Once an infant has been detected with abnormal thyroid screening tests, they should be recalled immediately for examination, and a venapuncture blood sample should be obtained for confirmatory serum testing… In the first few days of life, serum TSH [Thyroid Stimulating Hormone] can be as high as 39 mU/L, as a result of the TSH surge that occurs shortly after birth (this is the reason that the filter paper screening test cutoff is approximately 30 mU/L)… Although levels of all hormones are higher at 1-4 days of age, by 2-4 weeks of age they have fallen closer to the levels typically seen in infancy.”
Hypothyroidism Treatment
“Congenital hypothyroidism is one of the most common treatable causes of mental retardation. Studies have shown that the timing of therapy is crucial to neurologic outcome. Indeed, there is an inverse relationship between intelligence quotient (IQ) and the age at diagnosis. Even when diagnosed early, neurologic development may suffer if treatment is not optimized in the first two to three years of life. It is therefore important for these patients to receive early treatment and close follow up.” “The overall goal of therapy is ensure that these patients are able to have growth and mental development that is as close as possible to their genetic potential. This is achieved by rapidly restoring the free T4 and the TSH to the normal range and then maintaining clinical and biochemical euthyroidism.”
Hypothyroidism Medication
“Levothyroxine (l-thyroxine) is the treatment of choice. Although triiodithyronine (T3) is the biologically active form of the hormone, most T3 in the brain is formed from local deiodination of T4; thus, T3 replacement is not needed for normal neurologic functioning. In a study of forty seven infants given varying treatment doses of l-thyroxine, serum T3 normalized and remained normal regardless of the treatment dose used, again suggesting that treatment with l-thyroxine alone is adequate.” “Currently, only l-thyroxine tablets are approved for use in the United States. Thyroid suspensions prepared by individual pharmacies may result in unreliable dosing. In Europe, however, l-thyroxine drops have been successfully used.” “Some nutritional supplements or drugs are known to interfere with absorption of l-thyroxine.” “These include:
- Soy protein formulas
- concentrated iron
- calcium, aluminum hydroxide
- Cholestyramine and other resins
- fiber supplements
- Sucralfate
Finally, prolonged heat exposure may reduce the efficacy of l-thyroxine tablets.”
Congenital Hypothyroidism and Developmental Delay
“The dose and timing of thyroid hormone replacement are important in achieving optimal neurocognitive outcome. A delay in serum T4 normalization over one week can result in lower intelligence scores.” “Infants with severe congenital hypothyroidism are at greater risk for developmental delay. This has been illustrated in studies done in both Europe, the United States and Canada. Therefore, rapid replacement with adequate doses of l-thyroxine is particularly important… [A] study done in 61 infants compared early versus late treatment with low versus high dosing. Results showed that in infants with severe congenital hypothyroidism, only those treated early (< 13 days) and with higher doses (>9.5 mcg/kg/day) achieved normal psychomotor development at 10-30 months of age.” “[H]igher doses of l-thyroxine lead to better overall developmental outcomes. However…[studies note that] children on high dose l-thyroxine treatment had significant problems with hyperactivity, delinquency and aggression. Other studies have also shown that high serum T4 levels contribute to poorer attention in school aged children. These highlight the dangers of overtreatment in congenital hypothyroidism.” “Clinical evaluation should be performed every few months during the first three years of life along with frequent measurements of serum T4 or free T4 and TSH. The American Academy of Pediatrics recommends the following monitoring schedule.
- At two and four weeks after the initiation of l-thyroxine treatment
- Every 1-2 months during the first 6 months of life
- Every 3-4 months between 6 months and three years of age
- Every 6-12 months thereafter until growth is complete
- Four weeks after any change in dose
- More frequently if results are abnormal or non-compliance is suspected.”
“The serum T4 should normalize within one to two weeks and the serum TSH should become normal in most infants after one month of treatment.”
Prognosis
“Prior to the newborn screening era, when a diagnosis of congenital hypothyroidism was made after development of clinical manifestations, studies reported an inverse relationship between the age of diagnosis and IQ outcome. A study from Pittsburgh Children’s Hospital showed that if thyroid hormone treatment was started between birth and 3 months of age, the mean IQ was 89 (range 64 to 107); if treatment was started between 3 and 6 months of age, the mean IQ was 71 (range 35 to 96), while if treatment did not start until after 6 months of age, the mean IQ dropped to 54 (range 25 to 80) . A report from Sweden found that ‘in spite of an efficient National Health Care Program for infants, the diagnosis was delayed until after 3 months in 52 percent of cases’.” “The advent of newborn screening programs in the mid-1970s allowed earlier detection and treatment of infants with congenital hypothyroidism. Such efforts have been successful in achieving a much-improved neurocognitive outcome. Despite this, however, not all studies report a completely normal outcome. In a recent review of 51 published reports of IQ outcome in infants with congenital hypothyroidism as compared to sibling or classmate control subjects, 18 found no significant IQ difference, while 33 found a significant difference, with IQ ranging between 5 and 25 points lower in infants with congenital hypothyroidism. In evaluating important variables, there is evidence that age of onset of treatment, starting l-thyroxine treatment dose, and severity of hypothyroidism each plays an important role in neurocognitive outcome.”
Until next time, peace be with you, and stay healthy and safe!
Laura
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