What are the causes of hypothyroidism in children?

Childhood hypothyroidism—the underactivity of the thyroid gland—can arise from several distinct causes, broadly categorized as congenital or acquired. Congenital hypothyroidism, present at birth, is most commonly due to thyroid dysgenesis (e.g., thyroid agenesis, ectopy, or hypoplasia), accounting for approximately 85% of cases. Less frequently, it results from inborn errors of thyroid hormone synthesis (dyshormonogenesis), such as mutations in genes encoding thyroperoxidase, sodium-iodide symporter, or thyroid-stimulating hormone (TSH) receptor. Rarely, central (hypothalamic–pituitary) causes—like TSH deficiency or resistance—may be implicated.

Acquired hypothyroidism typically develops after infancy and is most often autoimmune in origin, specifically Hashimoto thyroiditis—an organ-specific lymphocytic infiltration leading to progressive thyroid destruction and elevated antithyroid peroxidase (TPO) and antithyroglobulin antibodies. Other acquired causes include iatrogenic factors (e.g., post-thyroidectomy or radioactive iodine therapy), neck irradiation, certain medications (e.g., lithium, amiodarone), iodine deficiency or excess, and infiltrative disorders such as sarcoidosis or hemochromatosis.

Early recognition is critical: untreated congenital hypothyroidism can result in severe neurodevelopmental impairment and growth failure, while delayed diagnosis in older children may manifest as fatigue, weight gain, cold intolerance, constipation, dry skin, delayed puberty, and poor school performance. Newborn screening programs—measuring TSH and/or thyroxine (T4) in dried blood spots—enable prompt detection and initiation of levothyroxine replacement, which is highly effective when started early and monitored regularly.