Enlargement of the thyroid gland, seen as a swelling in the neck, commonly due to deficiency of iodine in the diet or to the presence of goitrogens in foods. In such cases there is commonly underproduction of the thyroid hormones, i.e. hypothyroid goitre. Euthyroid goitre is a condition in which the enlargement of the thyroid gland is sufficient to compensate for a deficiency of iodine and permit normal production of thyroid hormones. In infancy, iodine deficiency can also lead to severe mental retardation, goitrous cretinism, with deafness. Supplementation with iodide often prevents the condition, hence the use of iodised salt.
Hyperthyroid goitre (thyrotoxicosis) is due to excessive stimulation of the thyroid gland, with overproduction of the thyroid hormones.