Hypothyroidism in Children

Deficiency of thyroid hormone secretion during fetal development and early in infancy results in infantile cretinism (congenital hypothyroidism). Untreated hypothyroidism is characterized in infants by respiratory difficulties, persistentjaundice, and hoarse crying and in older children by stunted growth (dwarfism), bone and muscle dystrophy, and mental deficiency.

Cretinism is three times more common in girls than in boys. Early diagnosis and treatment allow the best prognosis; infants treated before age 3 months usually grow and develop normally. Athyroid children who remain untreated beyond age 3 months and children with acquired hypothyroidism who remain untreated beyond age 2 suffer irreversible mental retardation; their skeletal abnormalities are reversible with treatment.

Causes

In infants, cretinism usually results from defective embryonic development that causes congenital absence or underdevelopment of the thyroid gland. The next most common cause can be traced to an inherited enzymatic defect in the synthesis of thyroxine (T4) caused by an autosomal recessive gene. Less frequently, antithyroid drugs taken during pregnancy produce cretinism in infants. In children older than age 2, cretinism usually results from chronic autoimmune thyroiditis.

Signs and symptoms

The weight and length of an infant with infantile cretinism appear normal at birth, but characteristic signs of hypothyroidism develop by the time he's 3 to 6 months old. In a breast-fed infant onset of most symptoms may be delayed until weaning because breast milk contains small amounts of thyroid hormone.

Typically, an infant with cretinism sleeps excessively, seldom cries (except for occasional hoarse crying), and is inactive. Because of this, his parents may describe him as a "good baby-no trouble at all." Such behavior actually results from lowered metabolism and progressive mental impairment. The infant with cretinism also exhibits abnormal deep tendon reflexes, hypotonic abdominal muscles, a protruding abdomen, and slow, awkward movements. He has feeding difficulties, develops constipation and, because his immature liver can't conjugate bilirubin, becomes jaundiced.

His large, protruding tongue obstructs respiration, making breathing loud and noisy and forcing him to open his mouth to breathe. He may have dyspnea on exertion; anemia; abnormal facial features-such as a short forehead; puffy, wide-set eyes (periorbital edema); wrinkled eyelids; and a broad, short, up­turned nose-and a dull expression, re-
sulting from mental retardation. His skin is cold and mottled because of poor circulation, and his hair is dry, brittle, and dull. Teeth erupt late and tend to decay early, body temperature is below normal, and pulse rate is slow.

In the child who acquires hypothyroidism after age 2, appropriate treatment can prevent mental retardation. However, growth retardation becomes apparent in short stature (due to delayed epiphyseal maturation, particularly in the legs), obesity, and a head that appears abnormally large because the arms and legs are stunted. An older child may show delayed or accelerated sexual development.

Diagnosis

In addition to a complete medical history and medical examination, diagnostic procedures for hypothyroidism may include blood tests to measure levels of thyroid hormones and the thyroid-stimulating hormones produced by the pituitary gland.

Treatment

Early detection is mandatory to prevent irreversible mental retardation and permit normal physical development.

Treatment of infants younger than age I consists of replacement therapy with orallevothyroxine, beginning with moderate doses. Dosage gradually increases to levels sufficient for lifelong maintenance. (Rapid increase in dosage may precipitate thyrotoxicity.) Doses are proportionately higher in children than in adults because children metabolize thyroid hormone more quickly. Therapy in older children includes levothyroxine.

Self-care tips

Early diagnosis of GHD is extremely important for the affected child. To obtain the best results, a child must be diagnosed and treated at a relatively young age. Successful treatment must begin before the child's bones fuse; once fusing has taken place, no additional growth is possible. Many children much shorter than their peers experience both physical and emotional problems. Communicate with your child, offer assistance when necessary, and remember to treat the child according to their age, not their size.