What is the treatment for congenital hypothyroidism?

Treatment of Congenital Hypothyroidism

Initiate levothyroxine immediately upon diagnosis at 10-15 mcg/kg/day, starting within the first 2 weeks of life to prevent intellectual disability. 1, 2

Immediate Treatment Protocol

Starting Levothyroxine

• Begin levothyroxine 10-15 mcg/kg/day orally as soon as congenital hypothyroidism is confirmed, without waiting for imaging studies to determine the underlying cause 2, 3
• Treatment must start within the first 2 weeks of life to prevent mental retardation and optimize neurocognitive outcomes 4, 2
• The FDA label confirms levothyroxine is indicated from birth for primary, secondary, and tertiary congenital hypothyroidism 1

Diagnostic Confirmation Requirements

• Confirm diagnosis with elevated serum TSH and low free T4 (or total T4) levels before starting treatment 5, 6
• Do not delay treatment to perform thyroid ultrasonography, scintigraphy, or thyroglobulin measurements—these can be done after initiating therapy 4
• Even if newborn screening is normal, measure serum TSH and free T4 when clinical signs are present (large posterior fontanelle, macroglossia, umbilical hernia, prolonged jaundice, constipation, lethargy, hypothermia) 2

Treatment Goals and Monitoring

Target Ranges

• Maintain free T4 in the upper half of the age-specific reference range, especially during the first 3 years of life 6, 2
• Keep TSH below 5 mIU/L 6
• Serum total T4 and free T4 should normalize within 1 week of starting therapy 3

Monitoring Schedule

• Monitor infants closely during the first 2 weeks of therapy for cardiac overload and arrhythmias 1
• Perform serial measurements of TSH and free T4 to guide dose adjustments 5
• Some infants will have persistently elevated TSH despite normalized T4/free T4 levels—this is acceptable as long as T4 remains in target range 5

Special Considerations

Dosing Nuances by Etiology

• Infants with dyshormonogenesis show more sensitive TSH suppression response to initial levothyroxine compared to those with thyroid dysgenesis, despite similar severity at diagnosis 3
• The standard dose of 10-14 mcg/kg/day effectively restores euthyroidism across all etiologies of congenital hypothyroidism 3

Critical Pitfalls to Avoid

• Never delay treatment to obtain imaging studies—thyroid ultrasound and scintigraphy should not postpone levothyroxine initiation 4
• Do not rely solely on newborn screening—70% of neonates worldwide lack access to screening, and clinical symptoms warrant testing regardless of screening results 2
• Do not underdose—inadequate initial dosing compromises neurocognitive outcomes, which are optimized when treatment begins promptly at appropriate doses 4, 2
• Do not discontinue levothyroxine during pregnancy in women with congenital hypothyroidism, as untreated hypothyroidism causes fetal neurocognitive impairment 1

Long-Term Management

Lifelong Treatment

• Levothyroxine is generally continued for life in patients with permanent congenital hypothyroidism 1
• Consistent follow-up and dose adjustments are essential as the child grows 2

Outcome Expectations

• When treatment starts within the first 2 weeks of life with adequate dosing, more than 90% of children with congenital hypothyroidism achieve normal neurocognitive development 4
• This makes newborn screening for congenital hypothyroidism the most successful population-based screening test in pediatrics 4