How to manage hyperthyroidism (high thyroid hormone levels) in an infant?

Management of Hyperthyroidism in Infants

The management of hyperthyroidism in infants requires prompt initiation of thioamide therapy (propylthiouracil or methimazole) with the goal of maintaining free T4 or FTI in the high-normal range using the lowest possible dosage. 1

Diagnosis and Initial Evaluation

• Laboratory testing: Measure TSH and free T4 (or FTI) levels to confirm hyperthyroidism 1
• Clinical assessment: Evaluate for:
  • Tachycardia
  • Poor weight gain despite adequate feeding
  • Irritability
  • Goiter (if present)
  • Eye findings (if Graves' disease)
  • Developmental status

Treatment Algorithm

First-line Medication Therapy

1. Thioamide therapy:

   • Either propylthiouracil or methimazole can be used 1
   • Recent studies show no significant differences between these medications in terms of efficacy or fetal anomalies 1
   • Dosing: Start with the lowest effective dose to maintain FT4 or FTI in the high-normal range 1
   • Monitoring: Measure FT4 or FTI every 2-4 weeks initially to adjust dosage 1

2. Symptomatic control:

   • Beta blockers (e.g., propranolol) can be used temporarily until thioamide therapy reduces thyroid hormone levels 1
   • Helps control tachycardia and other hypermetabolic symptoms

Monitoring and Follow-up

• Regular monitoring of thyroid function (TSH, free T4) every 2-4 weeks initially, then less frequently once stabilized
• Monitor for medication side effects:
  • Agranulocytosis: Watch for sore throat and fever; if present, obtain complete blood count and discontinue thioamide 1
  • Other side effects: Hepatitis, vasculitis, thrombocytopenia 1
• Growth and development assessment at each visit

Special Considerations

Neonatal Graves' Disease (Maternal Transfer)

• If mother has Graves' disease, the infant may develop transient hyperthyroidism due to transplacental passage of thyroid-stimulating antibodies
• Treatment is usually transient and rarely required long-term 1
• Inform the newborn's physician about maternal Graves' disease due to associated risk of neonatal thyroid dysfunction 1

Thyroid Storm

If severe hyperthyroidism with:

• Fever
• Tachycardia disproportionate to fever
• Altered mental status
• Vomiting, diarrhea
• Cardiac arrhythmia

Immediate treatment with:

• Propylthiouracil or methimazole
• Saturated solution of potassium iodide or sodium iodide
• Dexamethasone
• Supportive measures (oxygen, antipyretics, monitoring) 1

Treatment Alternatives

• Thyroidectomy: Reserved for infants who do not respond to thioamide therapy 1
• Radioactive iodine (I-131): Contraindicated in infants and children 1

Common Pitfalls and Caveats

1. Misdiagnosis: Neonatal hyperthyroidism may be confused with sepsis or other conditions causing tachycardia and irritability
2. Medication side effects: Always counsel parents about potential side effects of thioamide therapy, particularly agranulocytosis
3. Overtreatment: Excessive thioamide dosing can cause iatrogenic hypothyroidism, which can be equally harmful to infant development
4. Hyperemesis gravidarum: Can cause biochemical hyperthyroidism (undetectable TSH, elevated FTI) but rarely requires treatment 1
5. Delayed treatment: Untreated hyperthyroidism can lead to poor growth, developmental issues, and cardiac complications

By following this structured approach to diagnosis and management, most infants with hyperthyroidism can be effectively treated with good outcomes for growth, development, and quality of life.