What is the treatment for hyperthyroidism (overactive thyroid function) in a child?

Treatment of Hyperthyroidism in Children

The first-line treatment for hyperthyroidism (overactive thyroid function) in a child is methimazole (MMI), an antithyroid medication that inhibits thyroid hormone synthesis. 1, 2, 3

Diagnosis Confirmation

Before initiating treatment, confirm hyperthyroidism with:

• Thyroid function tests showing low TSH and elevated free T4 and/or T3
• Assessment for specific etiology (Graves' disease is most common cause in children)
• Thyroid ultrasound if nodular disease is suspected

Treatment Options

1. Antithyroid Medications

• Methimazole (MMI) is the preferred antithyroid drug for children 2, 3

  • Initial dosing:
    • Children <7 years: 0.7 mg/kg/day (higher weight-based dosing required) 4
    • Children 7-12 years: 0.5 mg/kg/day 4
    • Children >12 years: 0.44 mg/kg/day 4
  • Divided into 1-2 daily doses
  • Note: Younger children (<7 years) take longer to achieve euthyroid state (average 6.2 months vs 3.1 months in older children) 4

• Propylthiouracil (PTU) is generally avoided in children due to risk of severe liver injury

  • Only considered in special circumstances like thyroid storm or in the first trimester of pregnancy in adolescents

2. Definitive Treatment Options

For children with severe disease, recurrent hyperthyroidism after medication, or inability to tolerate antithyroid drugs:

• Radioactive iodine ablation

  • Most widely used definitive treatment in the United States 3
  • Generally reserved for older children/adolescents
  • Results in permanent hypothyroidism requiring lifelong thyroid hormone replacement

• Surgical thyroidectomy

  • Option for children with very large goiters or when radioactive iodine is contraindicated
  • Requires experienced pediatric surgeon to minimize complications

Monitoring and Dose Adjustments

1. Initial phase:

   • Check thyroid function tests (TSH, free T4, free T3) every 2-4 weeks
   • Adjust medication dose until euthyroidism is achieved
   • Monitor for adverse effects (rash, neutropenia)

2. Maintenance phase:

   • Once euthyroid, check thyroid function every 2-3 months
   • Typical duration of treatment: 12-18 months before trial off medication
   • Note: Approximately 50% of patients experience recurrence after discontinuation 5

Important Considerations

• Adverse effects of MMI:

  • Occur more frequently with higher doses (50% with ≥0.7 mg/kg/day vs 20% with <0.7 mg/kg/day) 2
  • Common: rash, neutropenia, gastrointestinal symptoms
  • Rare but serious: agranulocytosis, hepatotoxicity, vasculitis

• Special situations:

  • Breastfeeding mothers: MMI doses up to 30 mg/day appear safe for breastfed infants 6
  • Diabetes: Hyperthyroidism can worsen glycemic control; monitor glucose levels closely when treating 7

Treatment Duration and Follow-up

• Continue antithyroid medication for 12-18 months, then reassess
• Consider definitive therapy (radioactive iodine or surgery) for:
  • Recurrent hyperthyroidism
  • Poor medication adherence
  • Severe adverse reactions to antithyroid drugs
  • Large goiter causing compressive symptoms

Pitfalls to Avoid

1. Undertreating young children: Children <7 years require higher weight-based MMI doses and longer time to achieve euthyroidism 4

2. Overlooking adverse effects: Monitor complete blood count and liver function regularly, especially during the first 3 months of treatment

3. Inadequate follow-up: Regular monitoring is essential to adjust medication and detect recurrence

4. Ignoring comorbidities: Hyperthyroidism can exacerbate other conditions like diabetes and should be promptly treated 7