Which type of thyroid surgery results in lifelong hormone replacement therapy?

Total thyroidectomy involves the complete removal of the thyroid gland, which is responsible for producing thyroid hormones. Once the thyroid gland is removed, the body is unable to produce these hormones naturally. Consequently, patients who undergo total thyroidectomy require lifelong hormone replacement therapy to maintain normal metabolic function and prevent symptoms of hypothyroidism, such as fatigue, weight gain, and depression.

In contrast, subtotal thyroidectomy, where only a portion of the thyroid gland is removed, may allow for some residual function of the remaining thyroid tissue, potentially reducing or eliminating the need for hormone replacement therapy, depending on how much glandular tissue remains and how well it functions afterward.

Radioactive iodine therapy and antithyroid drugs are not types of surgery; they are medical treatments typically used for hyperthyroidism or certain thyroid-related conditions. These methods do not involve removing the thyroid and may not result in the need for lifelong hormone replacement.

Therefore, the requirement for lifelong hormone replacement therapy is a direct consequence of undergoing a total thyroidectomy, making it the correct answer.