What condition causes an overactive thyroid gland in cats?

Hyperthyroidism is the condition that results from an overactive thyroid gland in cats. This disorder is primarily caused by an increase in the production of thyroid hormones, which can lead to a variety of symptoms such as weight loss, increased appetite, hyperactivity, and excessive thirst and urination.

In cats, hyperthyroidism is most commonly seen in older individuals and is often due to benign tumors on the thyroid gland, which cause overstimulation. The excess hormones produced can significantly affect the cat's metabolism and overall health, making prompt diagnosis and treatment essential.

The other options, such as hypothyroidism, thyroiditis, and goiter, are related to thyroid conditions but are distinct from hyperthyroidism. Hypothyroidism involves an underactive thyroid gland, which leads to low hormone levels and a range of symptoms opposite to those seen in hyperthyroidism. Thyroiditis typically refers to inflammation of the thyroid gland and may not necessarily result in hyperactivity of the gland. Goiter is an enlargement of the thyroid gland and can occur in various conditions, including both hyperthyroidism and hypothyroidism, but it does not specifically indicate overactivity of the gland.