Acquired Hypothyroidism in Children

Background

• Acquired hypothyroidism is a hypometabolic state due to thyroid hormone deficiency from an autoimmune process, suppression of thyroid hormone synthesis, or damage to the thyroid gland.
• Acquired hypothyroidism can be primary (disorder of the thyroid gland), secondary (disorder of pituitary hormone secretion), or tertiary (disorder of the hypothalamus).
• The most common cause of acquired primary hypothyroidism is autoimmune thyroiditis, also called Hashimoto thyroiditis or chronic lymphocytic thyroiditis. Other causes of primary disease include suppression from medications, iodine deficiency, or removal or destruction of the thyroid gland.
• Autoimmune thyroiditis may be associated with other autoimmune disorders.
• Children and adolescents may present with growth failure, fatigue, cold intolerance, constipation or obstipation, developmental delay or learning difficulties, weight gain, or goiter.

Evaluation

• Check free thyroxine (free T4) and thyroid-stimulating hormone (TSH) in all children with suspected hypothyroidism.
  • Assess for elevated antimicrosomal antibodies (also called thyroid peroxidase antibodies) and thyroglobulin antibodies in children with low free T4 and elevated TSH.
  • Perform pituitary function testing in children with low free T4 and low-to-normal TSH.
• Diagnose primary hypothyroidism when free T4 is low and TSH is elevated. Diagnose autoimmune thyroiditis in patients with primary hypothyroidism who have elevated antimicrosomal antibodies (also called thyroid peroxidase antibodies) and/or thyroglobulin antibodies.
• Diagnose subclinical hypothyroidism when TSH is elevated but free T4 is normal and the patient is asymptomatic.
• Other types of acquired hypothyroidism can be diagnosed by medical history and the results of TSH, free T4, and if appropriate, the levels of other pituitary hormones and/or imaging studies.

Management

• Prescribe levothyroxine for treatment of all causes of acquired hypothyroidism (Strong recommendation).
  • Prescribe brand name levothyroxine or the same identifiable generic preparation consistently for early childhood hypothyroidism (Strong recommendation) and consider the same approach for all others (Weak recommendation).
  • Begin levothyroxine if thyroid-stimulating hormone (TSH) level is above and free T4 level is below the normal for age range.
    • Consider beginning at a lower dose and increasing dose slowly over several weeks to months, especially in children with long-standing, severe hypothyroidism.
    • Begin at full age-appropriate dose in children with rapid development of hypothyroidism, such as postsurgical or postradioiodine ablation of the thyroid gland.
  • Consider treatment with levothyroxine for patients with subclinical hypothyroidism (Weak recommendation).
  • Typical doses include:
    • 5-8 mcg/kg/day orally for infants aged 6-12 months
    • 4-6 mcg/kg/day orally for children aged 1-3 years
    • 3-5 mcg/kg/day orally for children aged 3-10 years
    • 2-4 mcg/kg/day orally for children > 10 years old
  • Adjust dose as needed based on age and weight, and the results of thyroid function tests (repeat abnormal tests before adjusting dose).
    • Keep the TSH concentration in the normal range (0.5-2 milliunits/L) and serum free T4 levels in the upper half of the normal range in children < 3 years old and at the midnormal range for children > 3 years old.
    • Consider a higher dose in children with a goiter to keep TSH in the low normal range (0.3-1 milliunits/L).
• Check free T4 and TSH after any change in dose or formulation in 4-6 weeks.
• Monitor serum free T4 and TSH every 6 weeks to 3 months in infants < 1 year old and every 3-6 months until puberty is complete.
• Consider yearly TSH monitoring in postpubertal children stabilized on long-term thyroxine therapy.