What is the treatment for hypothyroidism (underactive thyroid) causing delayed closure of the anterior fontanel?

Treatment of Hypothyroidism Causing Delayed Closure of the Anterior Fontanel

The definitive treatment for hypothyroidism causing delayed closure of the anterior fontanel is oral levothyroxine sodium at a starting dose of 10-15 mcg/kg per day. 1 This treatment must be initiated promptly to normalize thyroid function and allow proper development, including fontanel closure.

Diagnosis Confirmation

Before initiating treatment, confirm the diagnosis with:

• TSH and free T4 levels (elevated TSH and low free T4 indicate primary hypothyroidism)
• Clinical assessment for other signs of hypothyroidism:
  • Decreased activity and increased sleep
  • Feeding difficulties
  • Constipation
  • Prolonged jaundice
  • Myxedematous facies
  • Large fontanels
  • Macroglossia
  • Distended abdomen with umbilical hernia
  • Hypotonia

Treatment Protocol

1. Initial dosing: Start levothyroxine at 10-15 mcg/kg/day 1

   • Administer as a single daily dose
   • Give on an empty stomach, 30-60 minutes before breakfast with water 2
   • For infants who cannot swallow tablets, crush the tablet and suspend in 5-10 mL of water for immediate administration 2

2. Treatment goals:

   • Rapidly raise serum T4 above 130 nmol/L (10 μg/dL)
   • Normalize TSH levels
   • Maintain T4 or free T4 in the upper half of normal range 1

3. Monitoring schedule:

   • Check serum T4 (or free T4) and TSH every 1-2 months in the first year of life
   • Every 2-3 months in the second and third years 3
   • Adjust dose as needed based on laboratory results and clinical response

Important Considerations

• Timing is critical: Earlier treatment initiation (before 30 days of age) is associated with better neurocognitive outcomes 1

• Dose adjustment: The dose will decrease on a weight basis over time as the child grows 3

• Avoid overtreatment: Excessive levothyroxine can cause adverse effects including:

  • Craniosynostosis in infants with open fontanelles
  • Premature closure of epiphyses in growing children
  • Compromised adult height 2

• Medication interactions: Administer levothyroxine at least 4 hours apart from:

  • Calcium supplements
  • Iron supplements
  • Antacids
  • Other medications that may interfere with absorption 2

• Avoid soy-based formulas: These can decrease levothyroxine absorption 2

Expected Outcomes

With proper treatment, the anterior fontanel should begin to close at a more normal rate. The normal median time of closure for the anterior fontanel is 13.8 months, with a range of 4 to 26 months 4, 5.

The prognosis for infants detected early and started on appropriate treatment is excellent, with IQs similar to sibling or classmate controls 1. However, delayed treatment (beyond 30 days of age), insufficient levothyroxine dosing, or more severe initial hypothyroidism may result in poorer neurocognitive outcomes 1.

Common Pitfalls to Avoid

• Delayed diagnosis: Subtle clinical manifestations at birth may lead to missed diagnosis if not detected by screening
• Inadequate initial dosing: Starting with too low a dose may delay normalization of thyroid function
• Inconsistent administration: Giving levothyroxine with food or certain medications can reduce absorption
• Insufficient monitoring: Failure to check thyroid function regularly can lead to under or over-treatment
• Premature discontinuation: Treatment is typically lifelong for permanent hypothyroidism

Regular follow-up is essential to ensure optimal fontanel closure and overall development. If fontanel closure remains delayed despite normalized thyroid function, consider other potential causes such as increased intracranial pressure, skeletal anomalies, or normal variation 5.