Pediatric Thyroid Disease

Thyroid disease in children is rare, and should be handled by a surgeon with experience in pediatric thyroid disease.  Thyroid disease has a prevalence of about 37 per 1000 school-aged children, with goiter being the most common.  Goiter is gland enlargement (called “hypertrophy”) which occurs in about half of those with thyroid disease. Inflammation of the the thyroid gland (thyroiditis) is the second most common thyroid disease, followed by abnormalities of the thyroid hormone levels (“hyperthyroidism” and “hypothyroidism”), and finally thyroid nodules. Cancer of the thyroid is rare in children.

Goiter and Thyroiditis

A goiter is found in about 3% of the population of school-aged children. Goiters are classified as either diffusely enlarged or nodular. They can be associated with normal or abnormal thyroid hormone level. Most children with goiters have normal thyroid hormone level and surgical resection is rarely indicated.

The most common causes of a goiter in children fall into 3 classifications.

• Auto-Immune

Hashimoto’s thyroiditis (chronic lymphocytic), occurs most commonly in adolescent females. It is associated with other autoimmune disorders such as juvenile rheumatoid arthritis, Addison’s disease, and type I diabetes mellitus.

Graves’ disease develops insidiously over several months. Initial symptoms include nervousness, emotional lability, and declining school performance. This occurs 5 times more often in girls and the incidence steadily increases throughout childhood.

Simple colloid goiter also known as adolescent goiter or nontoxic goiter. The natural history of colloid goiter is not well known, but in one study in which adolescents were followed for 20 years, nearly 60% of the glands were became normal in size.

• Compensatory

Iodine deficiency goiter: rare in the USA.

Medication-induced: caused by drugs such as lithium by cause goiter.

Hormone or receptor defect goiter: rare cause of goiter.

• Inflammatory conditions

Acute suppurative thyroiditis: bacterial infection of the gland.

Subacute thyroiditis (also known as de Quervain’s) is caused by a viral infection and is very rarely seen in children.

Hyperthyroidism

Graves’ disease, also known as diffuse toxic goiter, is the most common cause of hyperthyroidism in childhood. In the newborn period symptoms may be delayed until 2 to 3 weeks after birth. Graves’ disease is caused by TSH receptor antibodies, which stimulate the thyroid follicles to increase iodide uptake and induce increased production and secretion of thyroid hormone. The diagnosis of Graves’ disease is further supported by the presence of TSH-stimulating immunoglobulins.Initial symptoms are listed above. As the disease progresses, there is weight loss, increased sweating, palpitations, heat intolerance, and malaise. True exophthalmos (bulging eyes) is unusual in in children, but a conspicuous stare is common.

Graves’ disease is currently managed by antithyroid medications, or the thyroid gland is ablated using either radioactive I¹³¹ or surgical resection. Most pediatric endocrinologists initiate therapy with anti-thyroid medications, although there is increasing use of radio ablation as the first line of treatment. The most commonly used medications are methimazole or propylthiouracil (PTU), which reduce thyroid hormone production by inhibiting follicle cell organification of iodide and coupling of iodotyrosines.

The most serious side effect of methimazole is an idiosyncratic agranulocytosis. This can occur at any time during the course of treatment. The onset of a sore throat with fevers should raise concern, and a neutrophil count should be obtained. Typically, the granulocyte count will rise in 2 to 3 weeks after stopping the drug, but in rare cases, fatal opportunistic infections have been reported. Other adverse reactions are; nausea, minor skin reactions, urticaria, arthralgias, arthritis, and fever.

The length of medical treatment is controversial. Usually, treatment is continued for 3 to 4 years. Remission of Graves’ disease is approximately 25% if medication is discontinued after 2 years of treatment, and the continuing remission rate is about 25% every 2 years. In most children, the remission of Graves’ disease will occur within 6 months of discontinuing antithyroid therapy. The resolution rate is decreased in children who have persistent detection of TSH receptor antibodies during and after treatment.

In patients who do not respond to antithyroid medication or who have a severe reaction to the medication, the thyroid gland must be ablated. Current methods of definitive treatment is surgical resection (subtotal thyroidectomy) or treatment with radioactive I¹³¹.

Hypothyroidism

In the United States, the most common cause is Hashimoto’s thyroiditis. . Less common causes include viral infections (de Quervain’s thyroiditis) and certain drugs like lithium.  Hypothyroidism can cause symptoms such as; feeling tired, weak, dry skin, brittle nails, cold intolerance, irregular menses, and constipation.  It is diagnosed by checking a TSH, T3, and T4 level.

Children with Hashimoto’s thyroiditis usually come to clinical evaluation because the thyroid gland is enlarged. The gland is generally pebbly or granular and may be mildly tender, and the diagnosis may be established by the showing a high-titer antithyroid antibodies.  The management of Hashimoto’s thyroiditis is usually expectant; as many as a third of adolescent patients will resolve spontaneously, with normalization of gland size and disappearance of the anithyroid antibodies.

Thyroid Nodules

Thyroid nodules are uncommon in children, but can be the presenting finding in cases of thyroid cancer.  Pediatric studies have shown that hte incidence of malignancy in these nodules to be 20% or less.  The differential diagnosis of a solitary thyroid nodule in children is;  Adenoma, Carcinoma, Thyroid cyst, Ectopic thyroid gland, Cystic hygroma, Thyroglossal duct remnant, and germ cell tumor.

Workup for a thyroid nodule includes a careful neck exam followed by a thyroid panel (TSH, T3, T4).  Ultrasonography may be helpful in determining the size and excluding other masses however it is unreliable at distinguishing benign from malignant nodule.  The use of FNA (fine needle aspiration) cytology to evaluate thyroid nodules is well established in adults, but the effectiveness of this technique is still being defined in children. Children usually will require sedation.  In adolescent patients, thyroid noduldes may be safely evaluated with FNA.

The results of FNA cytology either will indicate unequivocal cancer or a benign lesion or indeterminant.  Benign lesions can be followed with serial exams and ultrasounds.  Surgical resection should be performed if the nodule is malignant or indeterminant (on multiple FNA) or if a benign nodule is increasing in size.  If a cystic lesion disappears after aspiration, then surgery is deferred.  However, if the cyst recurrs, then it should be removed. Although the cyst fluid can be sent for cytology, the sensitivity of this test is probably low for detecting the presence of cancer.