A simple goitre is an enlargement of the thyroid gland. It's most commonly caused by an iodine deficiency. The body needs iodine to produce thyroid hormone. If you do not have enough iodine in your diet, the thyroid gets larger to try and capture all the iodine it can, so it can make the right amount of thyroid hormone. Other causes for simple goitre are: 1) the body's immune system attacking the thyroid gland (autoimmune problem); 2) certain medicines (lithium, amiodarone); 3) infections (rare); 4) cigarette smoking; 5) certain foods (soy, peanuts, vegetables in the broccoli and cabbage family); and 6) toxic nodular goiter, an enlarged thyroid gland that has a small, rounded growth or many growths called nodules, which produce too much thyroid hormone. Sometimes a goiter forms temporarily during puberty, pregnancy, or menopause.
Dyshormonogenetic goiter is caused by defective genes which prevent or decrease the synthesis of thyroid hormones due to biochemical defects. The final common pathway to goiter formation in each of these situation is due to hypersecretion of TSH which stimulates thyroid gland growth.