Congenital hypothyroidism is one of the most common endocrine disorders presenting at birth, as well as the most common treatable cause of mental retardation.
Before neonatal screening became standard in the United States during the past 40 years, congenital hypothyroidism often went unrecognized in many children.
The babies used to be missed because the signs and symptoms appear maybe months later, and by that time, often, treatment is less effective.
The overall incidence of CH ranges from 1:3000 to 1:4000 globally. Although the exact incidence of CH in India is unknown, a considerably older study conducted in 1998 reported the incidence to be 1:2640 of neonates.
The ICMR which screened for inborn metabolic disorders (2007–2012) in neonates from Delhi, Mumbai, Chennai, Hyderabad, and Kolkata reported an overall incidence for CH of 1:1130 newborns.
This study emphasized the need for adequate infrastructure, space, and resources as a part of the newborn screening.
Such a high incidence might be due to the advancement in screening methods as well as increased preterm birth rate.
Classification of Congenital Hypothyroidism:
Congenital Hypothyroidism has been classified into 3 categories-
1. Permanent Congenital Hypothyroidism: It is a sustained deficiency of thyroid hormone warranting lifetime treatment.
2. Transient Congenital Hypothyroidism: A temporary phase of thyroid hormone deficiency detected at the time of birth, which gets recovered to normal thyroid hormone level.
3. Syndromic hypothyroidism: A condition where Congenital Hypothyroidism is associated with impairment of other organ systems.
Etiology of Congenital Hypothyroidism
The most common underlying etiology of congenital hypothyroidism is thyroid dysgenesis, failure of the gland to develop or fully develop, accounting for 80% to 90% of cases.
The remaining 10% to 20% of cases are due to dyshormonogenesis, an abnormality in one of the steps necessary for thyroid hormone synthesis.
However, several less common conditions include defects in the thyroid hormone cell transporter, metabolism, and action at the receptor level.
Need for Newborn Screening Program
At the time hypothyroidism is detected, it is impossible to tell if it is going to turn out to be permanent or transient and detection as well as treatment of transient congenital hypothyroidism, also is beneficial, as thyroid hormone is critical for brain development within the first 3 years of life.
As many of the Indian states do not have government-funded screening programs, there is a need to encourage pediatricians and neonatologists to educate parents about the importance of screening for Congenital Hypothyroidism.
The current challenges associated with implementing newborn screening include developing adequate infrastructure, employing appropriate diagnostic methods, and the rising costs associated with the endeavor.
The goal of neonatal screening is to detect all forms of primary and secondary congenital hypothyroidism with an emphasis on the severe forms of congenital hypothyroidism.
Since diagnosis based on clinical findings is delayed in most instances because of few symptoms and signs of hypothyroidism in the newborn period are always overlooked, and delayed diagnosis leads to the most severe outcome of congenital hypothyroidism, namely, mental retardation.
Screening of primary congenital hypothyroidism is recommended by measuring thyroid-stimulating hormone (TSH) in cord blood or blood collected after 24 h of age although the best “window” for testing is 48–72 h of age after normal term delivery. Second sampling is recommended at 2 weeks of life for premature, sick, or low birth weight (<1.5 kg) neonates.
Furthermore, caregivers of neonates, discharged within 24 h of birth or in case of home delivery, are advised to visit the hospital for sampling, within 1 week.
Screening test for congenital hypothyroidism includes- T4 reflex TSH approach, TSH as the first test, and combined T4 and TSH. Screening should be done by age 48 hours to 72 hours of life.
Recommendations for Starting the Treatment
It is recommended that treatment be started immediately after the collection of confirmatory serum TSH and free T4, if the dried blood spot TSH concentration is at least 40 mU/L of whole blood.
However, if the concentration is less than 40 mU/L, then the clinician may postpone treatment for 1 to 2 days pending serum results. Regardless of TSH concentration, treatment is recommended if free T4 concentrations are below normal for the age of the infant. Further, if venous TSH concentration is persistently more than 20 mU/L, treatment should be started even if serum free T4 concentration is normal.
If the TSH [concentration] remains elevated more than a month, the children should be treated but re-evaluated at 3 years of age by having them come off treatment and getting repeat thyroid level tests a month later. The fact is that it may be transient, but it might not just last a couple of months, it may last 9 months.
If you are waiting for it to resolve on its own, thinking it’s transient, then you have a long period of hypothyroidism that could lead to a loss of a few IQ points. We really don’t want that to happen, though. Treatment for 3 years is better than losing IQ points.
The standard of care is essential to replace the thyroid hormone that is missing and restore it to normal. Initially, levothyroxine doses of 10 µg/kg to 15 µg/kg are recommended, depending on disease severity. The goal of treatment is to normalize T4within 2 weeks and TSH within 1 month. Free T4 should be measured after 1 week of therapy to determine whether serum concentrations are increasing appropriately, and dose should be adjusted based on clinical response and serum free T4 and TSH concentrations.
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