Hypothyroid
also Thyroid nodules, Thyroid Lab Scenarios

Congenital

•  Causes:

  • thyroid dysgenesis (90% of cases; aplasia/hypoplasia or ectopic)

  • inborn errors in thyroid hormone synthesis (usually autosomal recessive) – most common defect involves deficiency of thyroperoxidase enzyme which is responsible for converting iodide to iodine

  • TSH deficiency

  • TRH deficiency

  • maternally derived TSH-receptor blocking antibodies – treat babies with levothyroxine for about 6 months until antibodies have cleared

  • maternal antithyroid compounds

  • resistance to thyroid hormones

  • iodide deficiency

• Symptoms and signs:

  • prolonged jaundice - skin mottling

  • umbilical hernia - lethargy

  • constipation - macroglossia

  • large fontanel - distended abdomen

  • feeding problems - hoarse cry

  • hypotonia - slow deep tendon reflex

  • dry skin - hypothermia

  • also often associated with an increased risk of other congenital anomalies, especially congenital heart disease

Acquired

• Causes:

• autoimmune thyroiditis (also known as chronic lymphocytic, Hashimoto)

• most common etiology of acquired hypothyroidism in childhood
• due to T-cell mediated destruction of gland with circulating antibody
• may present with painless enlargement of gland, normal-sized gland, or absent gland if destroyed
• thyroid scan shows symmetrical thyroid enlargement with swiss-cheese appearance

• subacute thyroiditis

• usually associated with painful goiter
• typically present with hyperthyroid phase followed by a hypothyroid phase
• iodine uptake is low on thyroid scan during hyperthyroid phase

• acute suppurative

• TSH deficiency

• TRH deficiency

• post I-131 therapy

• post radiation therapy to head and neck

• post thyroidectomy

• resistance to TSH or thyroid hormones

• antithyroid drugs or compounds

• infiltrative disease of thyroid, e.g. cystinosis, histiocytosis X

• late presentation of congenital malformations such as ectopic thyroid gland

• Symptoms and signs:

  • decreased physical activity

  • constipation

  • dry skin

  • growth retardation

  • delayed adolescent maturity (but precocious puberty can occur)

  • myxedema

  • coarse hair

  • deep tone voice

  • slow relaxation phase in deep tendon reflexes

  • thyroid gland enlargement

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Short stature due to hypothyroidism is accompanied by other symptoms, such as constipation, dry skin, cold intolerance, and puffiness (myxedema). Laboratory evaluation reveals elevated thyroid-stimulating hormone and low thyroxine levels. Determination of bone age documents a delay in bone maturation.

CHLA Board Review 2005