What condition is characterized by an enlarged thyroid gland causing swelling at the base of the neck?

The condition characterized by an enlarged thyroid gland causing swelling at the base of the neck is hyperthyroidism. In hyperthyroidism, the overproduction of thyroid hormones can lead to an increase in the size of the thyroid gland, resulting in noticeable swelling often referred to as a goiter. This enlargement may also be accompanied by symptoms related to excess hormone levels, such as rapid heartbeat, weight loss, and increased sensitivity to heat.

The other conditions listed, while related to thyroid function, do not primarily cause the specific manifestation of an enlarged thyroid leading to neck swelling. Hypothyroidism typically results in a reduced function of the thyroid gland, which can sometimes also lead to a goiter, but it is not characterized by excessive enlargement due to overproduction of hormones. Thyroiditis refers to inflammation of the thyroid gland, which may also cause swelling, but it is often associated with pain or other inflammatory symptoms rather than the hormonal overactivity seen in hyperthyroidism. Cystitis, on the other hand, is an inflammation of the bladder and is unrelated to thyroid health.