Table of Contents
- Definition and Background of Congenital Hypothyroidism
- Etiology and Pathophysiology of Congenital Hypothyroidism
- Epidemiology of Congenital Hypothyroidism
- Presentation of Congenital Hypothyroidism
- Differential Diagnosis of Congenital Hypothyroidism
- Diagnosis of Congenital Hypothyroidism
- Management of Congenital Hypothyroidism
- Review Questions
Definition and Background of Congenital Hypothyroidism
The inadequate production of thyroid hormone in newborn infants causes the condition; Congenital Hypothyroidism. This condition may occur as a result of an inborn error in the thyroid metabolism, iodine deficiency, or an anatomic defect in the thyroid gland. Early diagnosis and treatment of congenital hypothyroidism can decrease the morbidity and complications from the condition.
Etiology and Pathophysiology of Congenital Hypothyroidism
Anatomic defects of the thyroid gland
Between the fourth and the tenth week of gestation, the Buccopharyngeal cavity develops the thyroid gland. This arises from the fourth branchial pouche and ends up in the neck as a bilobed organ. Thyroid dysplasia, aplasia, or ectopy may result from errors in the migration or the formation of the thyroid tissue.
Both iodine and tyrosine are required for the production of triiodothyronine (T3) and thyroxine (T4) from the thyroid gland. Thyroid peroxidase oxidizes iodide to iodine after being transported into the thyroid follicular cells by an active transport system.
Inborn errors of thyroid metabolism
Children with normal anatomic thyroid glands, may still suffer from congenital hypothyroidism due to other inborn errors of thyroid metabolism. These inborn errors may include:
- Lack of iodide uptake
- Abnormalities in TSH receptors
- Defects in thyroglobulin
- Deiodinase defect
- Defects in thyroid peroxidase
Epidemiology of Congenital Hypothyroidism
Congenital hypothyroidism in the United States
Congenital hypothyroidism incidence in the United States is reported to be approximately 1 in 4000 births.
Congenital hypothyroidism internationally
Data and reports from different countries indicate a close incidence to that of the United States; which is approximately 1 in 3000–4000 births. However, it is reported to be 1 in 1400–2000 in some countries in the Middle East.
Race and gender dependence of congenital hypothyroidism
The incidence appears to be higher among Hispanic females. It also appears to be higher in females in comparison to males with a female-to-male ratio of 2:1. Twin births appear to have a 12 times higher risk of developing the condition.
Presentation of Congenital Hypothyroidism
History of congenital hypothyroidism
Newborn infants who suffer from congenital hypothyroidism are usually born after term or at term. The diagnosis of the condition is more in countries where iodide deficiency is endemic.
Symptoms may include:
- Large anterior fontanelle
- Poor growth
- Small stature
- Poor feeding resulting in poor weight gain
- Decreased activity
- Hoarse cry
Physical examination of congenital hypothyroidism
The signs and features of hypothyroidism may not be present or prominent at birth, and they include:
- Macroglossia and coarse facial features
- Umbilical hernia
- Slow development
- Large fontanelle
- Dry skin
Screening newborns for congenital hypothyroidism
Newborn infants suffering from congenital hypothyroidism are usually identified during the first two or three weeks of life. Careful history and physical examination should be performed and testing should be repeated in order to confirm the diagnosis. IQs of infants suffering from obvious findings are 10 to 20 points lower than infants who do not have obvious findings.
Differential Diagnosis of Congenital Hypothyroidism
Congenital Hypothyroidism is distinguished by;
- Thyroxine-binding globulin deficiency
- Iodine deficiency
- Pediatric hypopituitarism
- Beckwith-Wiedermann syndrome
Diagnosis of Congenital Hypothyroidism
- Elevated levels of thyroid-stimulating hormone (TSH)
- Decreased levels of total and free thyroid hormone (T4)
- Neonatal and maternal antithyroid antibodies may be found
- Technetium-99m or iodine-123 may aid in genetic counseling and may be useful in determining the cause of hypothyroidism.
- Ectopic thyroid may be demonstrated by thyroid scans.
- Ultrasonography may be used as an alternative to thyroid scans.
TSH levels neonatal hypothyroidism screening may be helpful in areas where iodine deficiency is mild or not present.
Management of Congenital Hypothyroidism
Early diagnosis of the condition is very important for management. Medical treatment involves thyroid hormone replacement (levothyroxine is used).
In endemic areas where iodine deficiency is common, dietary iodide supplementation is advised and may help in preventing the condition.
It is advised to encourage activity among children who suffer from congenital hypothyroidism.
The correct answers can be found below the references.
1. A 9-week-old female newborn infant, who was born at home, is brought to the pediatrician by her mother. This is because she noticed that: she always feels cold, she sleeps too much, and her bowel movements are not very frequent. By physical examination, the pediatrician finds mild jaundice and hypotonia. Which of the following lab findings would you expect to see in this newborn?
- Inhibitory anti-TSH receptor antibodies
- Normal TSH, elevated reverse T3, and decreased total T4 and T3
- Elevated TSH, and decreased free and total T4
- Decreased TSH, and elevated free and total T4
- Stimulatory anti-TSH receptor antibodies
2. An obstetrician who works in a developing country delivers a baby who is suspected to have congenital hypothyroidism due to maternal iodine deficiency. Which sign of the following you would expect to find in this newborn?
- Umbilical hernia
- Mild jaundice
3. A 7-week-old American infant was born at term, following a normal and uncomplicated pregnancy. His chart reveals that he had indirect hyperbilirubonemia at birth. According to his mother, he suffers from poor feeding. By physical examination you notice that he suffers from hypotonia, lethargy, coarse facial features, and a protruding large tongue. What is the most likely cause of his presentation?
- Rett syndrome
- Iodine deficiency
- Thyroid dysgenesis
- Trisomy 21