Which organ is primarily affected by feline hyperthyroidism?

Feline hyperthyroidism primarily affects the thyroid gland, which is responsible for producing thyroid hormones that regulate various metabolic processes in the body. In cats, hyperthyroidism is typically caused by the overproduction of these hormones, most commonly due to a benign adenoma or enlargement of the thyroid gland. This leads to an increase in metabolism, resulting in symptoms such as weight loss, increased appetite, hyperactivity, and alterations in heart rate.

While the liver, kidney, and pituitary gland can be indirectly affected by the systemic changes caused by hyperthyroidism, the primary issue lies within the thyroid gland itself. The conditions associated with hyperthyroidism can lead to secondary complications involving other organs, but the source of the problem originates in the thyroid gland, confirming it as the primary organ affected by this condition in cats.