Question

Goitre can occur as a consequence of all the following except

• A. Iodine deficiency
• B. Pituitary adenoma
• C. Grave's disease
• D. Excessive intake of exogenous thyroxine

Answer 1

Answer: (D)

Excessive intake of exogenous thyroxine

A goitre is an enlargement of the thyroid gland. The thyroid gland is controlled by the pituitary gland. The pituitary prompts the thyroid to make its hormones including thyroxine ($T_4$) and triiodothyronine ($T_3$) by releasing thyroid-stimulating hormone (TSH). If a person's diet is low in iodine, the thyroid gland enlarges as it attempts to comply with the pituitary's demands. Another common cause is Graves disease, in which the immune system produces antibodies that act like TSH and stimulate the thyroid gland uncontrollably. The gland responds by producing an excessive amount of hormones. Thyrotropin (TSH) secreting pituitary adenomas are a rare cause of hyperthyroidism. Therefore, the correct answer is option D.