60. Goiters
Goiter refers to any abnormal enlargement of the thyroid gland. The most common cause worldwide is iodine deficiency. In the western world Hashimoto and Graves diseases are more frequent causes. Many conditions can cause enlargement of the thyroid, including neoplasms and inflammations.
Goiters are classified according to three parameters:
- The morphology (diffuse/nodular)
- The thyroid function (hypothyroid/euthyroid/hyperthyroid)
- The dignity of the thyroid (benign/malignant)
Etiology
- Iodine deficiency
- Hashimoto thyroiditis
- de Quervain thyroiditis
- Graves disease
- Thyroid cyst
- Thyroid adenoma
- Thyroid carcinoma
- Elevated TSH
- Pituitary adenoma
- Congenital goiter
Morphology
Goiters can be either nodular or diffuse, depending on whether the thyroid contains nodules or is diffusely enlarged.
Nodular goiters are often the result of neoplasms or cysts. There may be one or more nodules:
- Adenoma
- Carcinoma
- Cysts
Diffuse goiters are often the result of a compensatory hyperplasia of the thyroid tissue due to increased stimulation by TSH:
- Graves disease
- Hashimoto thyroiditis
- de Quervain thyroiditis
- Iodine deficiency
- Pituitary adenoma
Thyroid function
Goiters may accompany hypothyroidism, euthyroidism (normal thyroid function) or hyperthyroidism. In the context of goiter these conditions have special names:
- Goiter accompanied by hypothyroidism is known as hypothyroid goiter
- Goiter accompanied by euthyroidism is known as non-toxic goiter
- Goiter accompanied by hyperthyroidism is known as toxic goiter
Hypothyroid goiter is characterised by an enlarged thyroid gland and decreased T3 and T4 levels:
- Hashimoto thyroiditis
- de Quervain thyroiditis
- Congenital hypothyroid goiter
- Severe iodine deficiency
Non-toxic goiter is characterised by an enlarged thyroid and normal T3 and T4 levels:
- Mild to moderate iodine deficiency
Toxic goiter is characterised by an enlarged thyroid an increased T3 and T4 levels:
- Graves disease
- Toxic adenoma/carcinoma
Complications
Goiters are often accompanied by abnormal thyroid function, which of course causes its own symptoms. However, the enlargement of the thyroid can cause symptoms by itself:
- Compression of the trachea – extrathoracic obstruction
- Stridor
- Wheezes
- Dyspnoea
- Compression of the oesophagus
- Dysphagia
- Compression of the recurrent laryngeal nerve
- Hoarseness
Iodine deficiency
Iodine deficiency is more frequent in developing countries where fish and seafood are not a normal part of the diet. In most cases it causes non-toxic (euthyroid) goiter, but in severe deficiency it can cause hypothyroid goiter as well.
Iodine is essential for the production of thyroid hormone, so its deficiency causes hypothyroidism. This stimulates TSH production, which causes hyperplasia of the thyroid gland. This allows the thyroid to take up more iodine, which is often sufficient to ensure normal thyroid function. Only in severe iodine deficiency will this hyperplasia be insufficient, causing hypothyroid goiter.
Maternal iodine deficiency increases the risk for:
- Stillbirth
- Spontaneous abortion
- Malformations
- Small birthweight
- Perinatal mortality