Structure, function, signs, and symptoms

Typically, the history is the most important diagnostic aid in evaluating thyroid disorders, although the physical findings serve to bolster your suspicions. Thyroid size does not reflect thyroid function. First sort out the functional state: hypothyroid, hyperthyroid, or euthyroid (normal function). Then examine the thyroid to see whether it is too big or contains any lumps and to search for associated lymphadenopathy.

Causes of Childhood Hypothyroidism

The most common cause of hypothyroidism in childhood is autoimmune thyroiditis (Hashimoto’s disease, or lymphocytic thyroiditis). Lymphocytic infiltration causes firm diffuse enlargement of the thyroid and a pebbled surface. The anterior pituitary, sensing the lack of thyroid hormone (loss of feedback inhibition), increases the secretion of thyroid-stimulating hormone (TSH), causing the thyroid to enlarge further. Although the gland can grow in response to TSH, it cannot necessarily keep up in terms of thyroxine (T₄) production. Because the autoimmune process is destructive, some patients have a small or undetectable thyroid gland at presentation. A child with hypothyroidism secondary to hypothalamic-pituitary disease does not have thyroid enlargement (a goiter).

Congenital hypothyroidism is usually due to either absence of the thyroid or a hypoplastic thyroid that may be ectopic (located anywhere along the embryologic line of descent from the back of the tongue to the anterior neck.)

Case History 2

History. Shauna, age 15 years, says, “I was the tallest in my class in fifth grade, but I have not grown since then, and my periods haven’t started” (Fig. 16–5).

FIGURE 16–5 A, Shauna with the typical facial features of profound hypothyroidism. Note the puffy face and neck and the coarse, dry hair. B, Shauna after 4 months of treatment with thyroid hormone.

Your physical examination reveals all of the physical findings for hypothyroidism that are listed in Table 16–1. You particularly note the characteristic puffiness around Shauna’s upper face and eyes. In this case, because of profound hypothyroidism, there is also a more generalized swelling, including the neck.

TABLE 16–1 Causes of Precocious Puberty

Type of Precocious Puberty	Underlying Cause
Central	Idiopathic Hypothalamic hamartoma Germinoma (pinealoma) Other cerebral tumors or malformations Severe hypothyroidism Secondary to cranial irradiation
Gonadal	Benign precocious thelarche (? central) Ovarian cysts, benign McCune-Albright syndrome (polyostotic fibrous dysplasia of bone, ovarian cysts, large irregular café-au-lait spots) Leydig cell hyperplasia (familial testotoxicosis) Gonadal tumors (male and female) Isolated premature menses (? central)
Adrenal	Benign premature adrenarche Congenital adrenal hyperplasia Adrenal tumors
Iatrogenic	Exogenous sources

With treatment for hypothyroidism, Shauna’s menses start almost immediately. She grows an inch and loses 4 kg (9 lb) during 4 months of therapy.

In a few infants, hypothyroidism is caused by a congenital enzyme defect in thyroid hormonogenesis. In such instances, a goiter is present. In many countries, congenital hypothyroidism is now detected in the presymptomatic stage, before any significant intellectual deficit occurs, through blood spot screening between the second and fifth days of life. If congenital hypothyroidism is left untreated, the clinical manifestations may not become fully apparent until around the third month of life.

Key Point

Thyroid hormone is essential for adequate development of brain cell function and interneuronal connections. With absence of the hormone over the first few months of life, the infant suffers marked and irreversible developmental delay, the magnitude of the intellectual deficit increasing with each passing week. Universal newborn screening for hypothyroidism is therefore essential.

The infant with untreated congenital hypothyroidism has a low core body temperature, slow pulse rate, prolonged neonatal jaundice (because of poor hepatic conjugation of bilirubin), dry skin and hair, a large posterior fontanel (greater than 0.5 cm), poor head control, poor muscle tone, an enlarged tongue, a characteristically puffy face, and a hoarse cry (Fig. 16–6). The parents may report poor feeding and constipation. If acquired hypothyroidism develops after age 2 or 3 years, no permanent intellectual deficit is thought to occur.

FIGURE 16–6 Typical appearance of congenital hypothyroidism in a 3-month-old baby.

Acquired hypothyroidism must be ruled out in any child with unexplained growth retardation. The child’s appetite is generally diminished, yet there is a modest weight gain, leading to a decrease in height-to-weight ratio. Such children are not massively obese; by contrast, prepubertal obese children generally grow well in height. Constipation is a common feature. In children with type 1 diabetes mel litus, you must always rule out the coexistence of autoimmune thyroid disease, usually lymphocytic thyroiditis, because these disorders are commonly related.

Examining newborns and young infants

In a newborn or young infant, use a different technique to examine the thyroid. Place your hand under the child’s back, between the scapulae, and raise the baby’s shoulders, allowing the head to fall back gently until it rests on the examining table or a parent’s lap. If the thyroid is enlarged, this maneuver will expose it, allowing you to palpate with the second and third fingers of your other hand (Fig. 16–8).

FIGURE 16–8 Palpation of the thyroid gland in an infant.

Examining young children and adolescents

In the young child or adolescent, first observe the gland. Then, after gaining the child’s cooperation, palpate it. We generally examine from the front, as follows. Locate the cricoid cartilage, which is the smaller tracheal cartilage, just below the notched thyroid cartilage or Adam’s apple. Palpate just below the cricoid cartilage for a soft ribbon of tissue that moves with swallowing and is the normal isthmus. With practice you will become expert at finding the thyroid isthmus. Then rest both thumbs gently over the lobes of the thyroid, and ask the child to swallow. While the child swallows, move your thumbs with the child’s skin, up and down over the thyroid to outline its size. Note any nodules or irregularities you feel. You can also examine the thyroid in the traditional way, from behind the child: Place the second and third fingers of your examining hand over the gland to estimate its size, and ask the child to swallow. We often joke with older children who hate to have their necks touched that we have never choked anyone and are not allowed to!

Always measure and record the gland size so that any significant changes between visits are documented. With a measuring tape, measure from upper to lower pole and the greatest vertical dimension of the isthmus. Record the results in diagrammatic form, indicating any nodules or other irregularities.

The normal thyroid weight in grams corresponds approximately to the child’s age in years; a normal adult gland weighs 20 to 25 g and is the size of your thumb from the distal interphalangeal joint to the tip. The thyroid can be palpated in most older children. Because its normal consistency is soft, the contours can barely be seen, and the gland is rather flat when the child hyperextends the neck. Once the thyroid gland becomes firm, as in autoimmune thyroiditis (Hashimoto’s disease), or hard, as in a carcinoma, you should recognize the difference in consistency, even though enlargement may not be striking. Some carcinomas, however, may not be hard to the touch because consistency is not always a reliable diagnostic sign.

Most midline neck masses are thyroid glands or thyroid remnants. A central rounded midline mass between the thyroid and the chin is almost certain to be a thyroglossal duct cyst (Fig. 16–9), derived from a remnant of the thyroglossal duct, which runs from the foramen cecum of the tongue downward to the cricoid cartilage during fetal development. When the child sticks out the tongue, the mass moves upward. The child may present initially with an infected thyroglossal duct cyst. Sometimes, the gland fails entirely to migrate downward from the foramen cecum and manifests clinically as an oval or rounded midline mass at the base of the tongue (Fig. 16–10). This lingual thyroid usually represents all of the thyroid that the child has. Most lingual thyroids are treated with daily therapy using l-thyroxine, which suppresses pituitary thyrotropin (TSH) secretion, causing the lump to shrink markedly.

FIGURE 16–9 Thyroglossal duct cyst, a midline neck mass.

FIGURE 16–10 Thyroid scan in an infant demonstrating uptake of the radionuclide at the base of the tongue in a lingual thyroid (arrow).

The thyroid may be absent, small, ectopic, or enlarged. If both lobes are enlarged fairly symmetrically, it is described as diffusely enlarged. The normal gland may have slight undulations on palpation, but if you find one or more distinct lumps, the child has either a solitary nodule or a multinodular goiter.

A diffusely enlarged, nontender gland that is soft to somewhat firm in consistency is compatible with Graves disease. By contrast, a tender, diffusely swollen gland in a child who withdraws when the gland is touched is likely to represent subacute thyroiditis attributed to a viral cause. Thyroid-stimulating antibodies interact with the TSH receptor on the thyroid cell, producing the constant stimulation of Graves disease. In subacute thyroiditis, disrupted cells produce a sudden thyroid hormone discharge, causing a transient hyperthyroid period, which is often followed by a longer hypothyroid state, then by euthyroidism within 3 to 6 months. A similar sequence is seen in a condition called silent thyroiditis, so called because it is not painful. Silent thyroiditis is most common in the postpartum period but does occur at all ages and in both sexes; it has an autoimmune etiology.

If one or more nodules are found in a child with hyperthyroidism, the cause is probably a benign adenoma, called toxic nodular goiter, which is overproducing thyroid hormone. This condition is seen more commonly in adults. The discrete smooth, oval or round nodules are firmer than the surrounding gland but not rock-hard. When the child swallows, they move up and down and are not fixed to extrathyroidal tissues. Rare TSH-secreting pituitary adenomas can cause diffuse thyroid enlargement and systemic signs of hyperthyroidism but without the eye findings characteristic of autoimmune (Graves) disease.

An eye examination yields important clues for diagnosis and management of thyroid disease. In hyperthyroidism, the palpebral fissures are widened and blinking is diminished, giving the child a staring appearance. In autoimmune Graves disease, the eye muscles can swell to several times their normal size, and the retro-orbital fat pad enlarges, causing the eye to bulge out of the orbit (proptosis), often with injection (prominent small surface vessels) and edema of the bulbar conjunctiva (chemosis). Because individuals with proptosis have difficulty closing their lids, corneal ulceration may occur, causing red, sore eyes, particularly in the morning. Ask the parent whether the child closes the eyes when sleeping. Without adequate tears and with open lids, the cornea becomes dry and vulnerable to ulceration. Enlarged ocular muscles produce an imbalance of extraocular muscle function, sometimes sufficient to cause diplopia, which may be unrecognized by affected patients until they are asked to look upward and outward, the direction of gaze in which diplopia can first be elicited. Usually, there is some loss of convergence, and the child cannot cross the eyes to the usual extent when trying to follow the physician’s finger as it is moved toward the nose.

Thyroid bruits are characteristic of Graves disease, but this sign is not very useful in children. The problem with auscultating the neck in children is that if you press hard enough with the stethoscope, you can make anything whistle.

Infants may be born with neonatal hyperthyroidism from transplacental passage of thyroid-stimulating immunoglobulin, an antibody produced in a mother who has active or treated Graves disease with persistent circulating antibody. Although these babies have the same signs as older children, they are more likely to have hyperthermia and cardiac tachyarrhythmias and to develop congestive heart failure.