Description
Congenital hypothyroidism (CH) is a condition in which the thyroid gland is underactive from birth. The thyroid gland produces hormones that regulate metabolism, growth, and development. CH is the most common endocrine disorder in newborns, affecting about 1 in 2,000 to 4,000 births. The condition can lead to intellectual disability and other developmental problems if left untreated.Newborn screening tests can detect CH, and early treatment can prevent complications. CH can be caused by genetic or environmental factors. The most common cause of CH is an underdeveloped or absent thyroid gland. Other causes include defects in the hormone synthesis pathway and maternal thyroid disease. Symptoms of CH may not be apparent at birth but can include poor feeding, constipation, and a hoarse cry. If left untreated, CH can lead to growth failure, intellectual disability, and other developmental delays.
Treatment for CH involves lifelong hormone replacement therapy with synthetic thyroid hormone.
Résumé
- Congenital hypothyroidism, occurring in approximately 1 in 2000 to 3000 newborns, is the most common preventable cause of mental retardation. Early diagnosis and management, particularly in newborns, are crucial to prevent long-term cognitive and developmental issues. Thyroid hormones are essential for growth, brain development, and overall well-being, especially in children.
- The thyroid gland, the first endocrine structure to develop, originates from the pharyngeal pouches and migrates from the back of the tongue to its final position inferior to the thyroid cartilage. Maternal transfer of thyroid hormones is crucial for fetal brain growth until the fetus begins producing its own hormones around mid-gestation.
- The hypothalamic-pituitary-thyroid axis regulates thyroid hormone production. TRH from the hypothalamus stimulates TSH release from the pituitary, which in turn stimulates the thyroid gland to produce T3 and T4. T3 is the active form, converted from T4 in peripheral tissues. A negative feedback loop prevents overproduction of thyroid hormones. Neonates experience a TSH surge in the first 24-48 hours, which can affect newborn screening results.
- Thyroid hormone synthesis requires iodine. Iodine is transported into the thyroid cells via the sodium iodide symporter, where it is oxidized and combined with tyrosine to form mono-iodotyrosine (MIT) and di-iodotyrosine (DIT). These couple to form T3 and T4. Thyroglobulin transports these hormones into the circulation. The remaining iodine is recycled.
- Thyroid hormones have diverse actions, including stimulating lipolysis, increasing glucose absorption, aiding bone development, and regulating basal metabolic rate. Inadequate thyroid hormone levels can lead to weight gain, poor growth, and intellectual disabilities.
- Etiologies of congenital hypothyroidism include permanent forms (primary and central), transient forms (maternal antibodies, iodine deficiency or excess, antithyroid medications), and less common forms (central hypothyroidism, thyroid hormone resistance). Thyroid dysgenesis, including agenesis, hypoplasia, or ectopic thyroid, is the most common permanent cause.
- Thyroid dyshormonogenesis, where the gland is present but hormone synthesis is impaired, accounts for 10-15% of cases. Mutations in genes encoding enzymes or transporters involved in thyroid hormone biosynthesis, such as thyroid peroxidase (TPO) deficiency and Pendred syndrome, can cause this.
- Central hypothyroidism results from insufficient stimulation of the thyroid gland due to hypothalamic or pituitary dysfunction. Transient hypothyroidism can be caused by iodine deficiency/excess, maternal antibodies, or certain medications. Isolated hyperthyrotropinemia, elevated TSH with normal T4, can occur in preterm infants due to immaturity of the hypothalamic-pituitary axis.
- Symptoms of hypothyroidism in newborns may include dry skin, coarse facial features, enlarged tongue, protruding abdomen, umbilical hernia, constipation, and poor feeding. However, many neonates may be asymptomatic, emphasizing the need for newborn screening.
- Evaluation of a newborn with suspected hypothyroidism includes a detailed history, physical examination, thyroid hormone testing, and imaging studies. Hearing screening is recommended due to the association with hearing loss. Newborn screening is critical because it's simple, reliable, and allows for timely treatment.
- Newborn screening can be performed using cord blood or postnatal heel prick samples. The timing of sample collection is important to avoid false positives due to the TSH surge. A TSH-based screening is common and very sensitive. Any TSH result that is more than 20 should be recalled for evaluation.
- Treatment of congenital hypothyroidism involves levothyroxine supplementation, with a starting dose of 10-16 mcg/kg/day. The tablet should be crushed and mixed with a small amount of breast milk, formula, or water. The dosage should be administered first thing in the morning, avoiding concurrent administration with iron or calcium supplements.
- Follow-up appointments are crucial to monitor growth, development, and thyroid hormone levels. The goal is to maintain free T4 in the upper level of the normal range and TSH in the lower half. The child should be followed up every few months. Re-evaluation for permanent vs transient hypothyroidism is assessed at three years of age.
- Down syndrome children are at increased risk for thyroid disorders, including congenital hypothyroidism. Subclinical hypothyroidism should be treated in Down syndrome children.
Exemple de certificat
À propos des intervenants
Dr Tejasvi Sheshadrissa
,MD Paediatrics,Consultant Paediatric Endocrinologist, Sparsh Hospitals, Bangalore
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