(See also Overview of Thyroid Function.)
Simple nontoxic goiter, the most common type of thyroid enlargement, is frequently noted at puberty, during pregnancy, and at menopause. The cause at these times is usually unclear. Known causes include
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Intrinsic thyroid hormone production defects
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Ingestion of foods that contain substances that inhibit thyroid hormone synthesis (goitrogens, eg, cassava, broccoli, cauliflower, cabbage), as may occur in countries in which iodine deficiency is common
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Drugs that can decrease the synthesis of thyroid hormone (eg, amiodarone or other iodine-containing compounds, lithium)
Iodine deficiency is rare in North America but remains the most common cause of goiter worldwide (termed endemic goiter). Compensatory small elevations in thyroid-stimulating hormone (TSH) occur, preventing hypothyroidism, but the TSH stimulation results in goiter formation. Recurrent cycles of stimulation and involution may result in nontoxic nodular goiters. However, the true etiology of most nontoxic goiters in iodine-sufficient areas is unknown.
Symptoms and Signs
Diagnosis
In the early stages, thyroidal radioactive iodine uptake may be normal or high with normal thyroid scans. Thyroid function test results are usually normal. Thyroid antibodies are measured to rule out Hashimoto thyroiditis.
In endemic goiter, serum TSH may be slightly elevated, and serum T4 may be low-normal or slightly low, but serum T3 is usually normal or slightly elevated.
Thyroid ultrasonography is done to determine whether there are nodules that are suggestive of cancer.
Treatment
In iodine-deficient areas, the following eliminate iodine deficiency:
Goitrogens being ingested should be stopped.
In other instances, suppression of the hypothalamic-pituitary axis with thyroid hormone blocks thyroid-stimulating hormone (TSH) production (and hence stimulation of the thyroid). Moderate doses of L-thyroxine (100 to 150 mcg orally once a day depending on the serum TSH) are useful in younger patients to reduce the serum TSH to the low-normal range.
L-Thyroxine is contraindicated in older patients with nontoxic nodular goiter, because these goiters rarely shrink and may harbor areas of autonomy so that L-thyroxine therapy can result in hyperthyroidism.
Large goiters occasionally require surgery or iodine-131 to shrink the gland enough to prevent interference with respiration or swallowing or to correct cosmetic problems.
Key Points
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Thyroid function is usually normal.
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When the cause is iodine deficiency, iodine supplementation is effective treatment.
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Blocking thyroid-stimulating hormone production by giving L-thyroxine is useful in younger patients to halt stimulation of the thyroid and shrink the goiter.
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Surgery or iodine-131 may be needed for large goiters.
