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Introduction
- Congenital hypothyroidism is one of the most common preventable causes of mental retardation
- Acquired hypothyroidism is the absence or decrease in the production of thyroid hormone
Etiology
Acquired Hypothyroidism
- Primary acquired hypothyroidism: Caused by generalized tissue resistance to thyroid hormone & disorders that affect the thyroid gland directly
- Responsible for majority of hypothyroid cases
- Etiologies: Chronic autoimmune (Hashimoto’s) thyroiditis, iodine deficiency/excess, thyroid surgery, radioactive iodine therapy, external irradiation, infiltrative disorders, drugs, agenesis/dysgenesis of the thyroid
- Central acquired hypothyroidism: Caused by hypothalamic or pituitary disorders
- Etiologies: Pituitary tumors, metastasis, hemorrhage, necrosis, aneurysms, surgery/trauma, infiltrative disorders, infectious diseases, chronic lymphocytic hypophysitis, other brain tumors, congenital abnormalities, defects in thyrotropin-releasing hormone (TRH), thyroid-stimulating hormone (TSH) or both
- May also be classified as congenital or acquired (symptoms manifest after a period of normal functioning)
Congenital Hypothyroidism
- Permanent cases result from dysgenesis/agenesis of thyroid gland or a defect in thyroid hormonogenesis
- Transient cases due to transplacental passage of maternal medication, maternal blocking antibodies or iodine deficiency/excess
- Rare cases due to central hypothyroidism
Signs and Symptoms
Acquired Hypothyroidism
- Goiter
- Lethargy, ataxia, dull facial expressions
- Slow growth & short stature, delayed bone age & dentition
- Immature upper to lower body proportions
- Cool, dry, jaundiced skin; dry, coarse hair, brittle nails
- Obstructive sleep apnea (OSA)
- Cold intolerance
- Constipation, galactorrhea
- Hoarseness
- Memory & mental impairment, decreased concentration, depression
- Precocious sexual development, irregular or heavy menses, infertility
- Hyperlipidemia
- Myxedema
- Weight gain despite decreased appetite
- Bradycardia
Congenital Hypothyroidism
- Large fontanelles
- Prolonged indirect jaundice, constipation
- Hypothermia; cool, dry skin
- Noisy respirations, hoarse cry
- Goiter
- Delayed relaxation of deep tendon reflexes, decreased activity level
- Elevated birth weight despite poor feeding
- Pooling of secretions, large protruding tongue
- Myxedema of eyelids, hands, scrotum
- Bradycardia
