Hypothyroidism in children
Hypothyroidism in children: Excerpt from Handbook of Diseases
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, persistent jaundice, 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 years 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, resulting 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
A high serum level of thyroid-stimulating hormone (TSH) associated with low triiodothyronine and T4 levels points to hypothyroidism. Because early detection and treatment can minimize the effects of cretinism, many states require measurement of infant thyroid hormone levels at birth.
Thyroid scan and 131I uptake tests show decreased uptake levels and confirm the absence of thyroid tissue in athyroid children. Increased gonadotropin levels are compatible with sexual precocity in older children and may coexist with hypothyroidism. An electrocardiogram shows bradycardia and flat or inverted T waves in untreated infants. Hip, knee, and thigh X-rays reveal the absence of the femoral or tibial epiphyseal line and delayed skeletal development that’s markedly inappropriate for the child’s chronological age. A low T 4 level associated with a normal TSH level suggests hypothyroidism secondary to hypothalamic or pituitary disease, a rare condition.
Treatment
Early detection is mandatory to prevent irreversible mental retardation and permit normal physical development.
Treatment of infants younger than age 1 consists of replacement therapy with oral levothyroxine, 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.
Special considerations
Prevention, early detection, comprehensive parent teaching, and psychological support are essential. Know the early signs. Be especially wary if parents emphasize how good and how quiet their new baby is.
❑ During early management of infantile cretinism, monitor blood pressure and pulse rate; report hypertension and tachycardia immediately. Remember, however, that the normal infant heart rate is about 120 beats/minute. If the infant’s tongue is unusually large, position him on his side and observe him frequently to prevent airway obstruction. Check rectal temperature every 2 to 4 hours. Keep the infant warm and his skin moist.
❑ Inform the parents that the child will require lifelong treatment with thyroid supplements. Teach them to recognize the signs of overdose, such as rapid pulse rate, irritability, insomnia, fever, sweating, and weight loss. Stress the need to comply with the treatment regimen to prevent further mental impairment.
❑ Provide support to help the parents deal with a child who may be mentally retarded. Help them adopt a positive but realistic attitude and focus on their child’s strengths rather than his weaknesses. Encourage them to provide stimulating activities to help the child reach his maximum potential. Refer them to appropriate community resources for support.
Book Source Details
- Book Title: Handbook of Diseases
- Author(s): Springhouse
- Year of Publication: 2003
- Copyright Details: Handbook of Diseases, Copyright © 2003 Lippincott Williams & Wilkins.
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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More About This Book:
Title: Handbook of Diseases
Authors: Springhouse
Publisher: Lippincott Williams & Wilkins
Copyright: 2003
ISBN: 1-58255-266-5
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