Hypothyroidism is the most common disturbance of thyroid function in children; acquired hypothyroidism is most often caused by autoimmune thyroiditis . As in adults, acquired hypothyroidism can be caused by both thyroid disease (primary hypothyroidism) and hypothalamic-pituitary disease (central hypothyroidism); furthermore, primary hypothyroidism may be either subclinical (high serum thyroid stimulating hormone [TSH] and normal serum free thyroxine [T4] concentrations) or overt (high serum TSH and low serum free T4 concentrations). Whatever its cause, hypothyroidism in children can have deleterious effects on growth, pubertal development and school performance.
The most common manifestation of hypothyroidism in children is declining growth velocity, often resulting in short stature. The growth delay tends to be insidious in onset, and it may be present for several years before other symptoms occur, if they occur at all . Thus, any child with declining growth velocity should be evaluated for hypothyroidism. (See "Diagnostic approach to short stature".)
Another common feature is altered school performance. Performance often declines, but it improves in some children, perhaps because they are less active and, therefore, less easily distracted and better able to concentrate. One reason for delay in diagnosis is that parents see the latter changes as positive.
Other common symptoms are sluggishness, lethargy, cold intolerance, constipation, dry skin, brittle hair, facial puffiness, and muscle aches and pains. If the cause is hypothalamic or pituitary disease, the child may have headaches, visual symptoms, or manifestations of other pituitary hormone deficiencies. (See "Clinical manifestations of hypothyroidism".)
The most common physical finding at presentation is a diffusely enlarged thyroid gland (goiter). In one series from Israel, a noticeable goiter was present in 39.5 percent of children with autoimmune thyroiditis . Alternatively, the thyroid gland may be normal in size or not palpable at all. Abnormalities on physical examination include short stature, apparent overweight (more fluid retention than obesity), puffy facies with a dull, placid expression, bradycardia, pseudohypertrophy of the muscles, and delayed deep tendon reflexes.