Goiter is an abnormal enlargement of the thyroid gland.
The thyroid gland is the organ located in front of the trachea comprised of 2 lobes connected by the isthmus. Goiter is a term defining the enlarged thyroid gland that presents as the neck swelling. In turn, the goiter may be diffuse (when the whole gland appears enlarged) or nodular (the gland has nodular structure). The gland enlargement doesn’t mean that its function is impaired – individuals with goiter may have normal thyroid function (nontoxic goiter, euthyroidism), or the thyroid may produce increased amounts of the thyroid hormones causing hyperthyroidism (toxic goiter) or decreased amounts of the hormones leading to hypothyroidism. However, the presence of the goiter means that there is any underlying disorder which causes the gland enlargement.
Depending on the size of the thyroid gland 3 classes of goiter are established:
- Class I: the thyroid enlargement is detected only by palpation;
- Class II: the goiter can be seen;
- Class III: very large goiter which compresses the trachea;
Causes enlarged thyroid gland
- Genetic thyroid enzyme defects and iodine deficiency reduce the efficiency of thyroid hormone synthesis resulting in the increased levels of TSH, which stimulate the growth of the thyroid gland as a compensatory mechanism;
- Iodine overconsumption;
- Consumption of drug goitrogens (lithium, iodide, propylthiouracil or methimazole, sulfonamides, amiodarone, interferon-alpha, interferon-beta, interleukin-2) or food goitrogens (Brussels sprouts, broccoli, cauliflower, turnips, cassavas, cabbage, peanuts, spinach, strawberries, etc.);
- In Grave’s disease the goiter is mediated by the thyroid-stimulating immunoglobulins, which act on the TSH-receptors on the thyroid gland;
- Hashimoto’s thyroiditis leads to the impaired synthesis of the thyroid hormones, which consequently result in the increased TSH production by the pituitary and the growth of the thyroid gland. On the other hand, the thyroid enlargement in Hashimoto’s thyroiditis may be related to the lymphocytic infiltration of the gland;
- Other thyroiditis, both acute and chronic, leads to the enlargement of the gland due to the inflammation and its infiltration with the leukocytes;
- Thyroid cancer or benign thyroid neoplasms may present with the enlargement of the gland;
- Smoking is known to decrease the iodine absorption and, respectively, increase the risk of developing enlarged thyroid gland;
- Hormonal changes during pregnancy, puberty, and menopause associated with the higher iodine demand may also lead to the thyroid enlargement;
Nodular thyroid disease
Thyroid nodules are common lesions seen in about 50% of the adults, although most of them are <1 cm in diameter. There may be only one nodule (solitary nodule) or multiple nodules, which may secrete hormones (functional nodules) or not (nonfunctional lesions).
Diffuse nontoxic (simple) goiter
When the thyroid appears diffusely enlarged in the absence of hyperthyroidism the goiter is referred to as diffuse nontoxic. Typically diffuse goiter is caused by the iodine deficiency. When more than 5% of the population is affected the disorder is defined as the endemic enlarged thyroid gland. Consumption of food containing goitrogens may also cause the diffuse goiter.
Nontoxic goiter is usually asymptomatic. The gland itself is symmetrically enlarged, and soft. If the gland is markedly enlarged it may compress the trachea and esophagus, causing the feeling of pressure in the neck, tightness, choking sensation, hoarseness, difficulties while swallowing.
Toxic multinodular goiter
Toxic multinodular goiter occurs when the thyroid nodules begin to produce excessive amounts of the thyroid hormones causing hyperthyroidism.
Diffuse toxic hyperplasia (Grave’s disease)
Diffuse enlargement of the thyroid gland accompanied by the excessive thyroid hormone production stimulated by the autoantibodies that attach to the TSH receptors is known as the Grave’s disease.
High levels of thyroid hormones (hyperthyroidism) are characterized by the unintentional weight loss accompanied by the increased appetite, protruding eyeballs, rapid heartbeat, trembling of the hands and fingers, excessive sweating increased sensitivity to heat and anxiety.
Goiter treatment depends on the cause of the thyroid enlargement and thyroid function.
- The mild thyroid enlargement with the normal function of the gland does not require any treatment, although a person should be observed. Levothyroxine suppressive therapy may be used to decrease the gland volume in case of euthyroid goiter. Goiter caused by the iodine deficiency should be treated with small doses of iodide (Lugol’s Iodine or KI solution).
- If the gland produces excessive amounts of thyroid hormones suppressive therapy with radioactive iodine is recommended. Anti-thyroid drugs may be used to reduce hormone levels.
- Levothyroxine is also given in case of hypothyroidism.
- Surgical resection is indicated for large goiters that compress the trachea or for cosmetic reasons. Thyroidectomy should be followed by replacement therapy with levothyroxine.