Thickening of the thyroid isthmus is most likely caused by iodine deficiency. Insufficient iodine intake prevents the synthesis of sufficient amounts of thyroxine, which in turn causes increased secretion of TSH, or thyroid stimulating hormone, in the pituitary gland, thus stimulating the hyperplasia of the isthmus and causing the thickening of the isthmus. In this case, if there are no obvious clinical symptoms, observation can be given and more iodine-rich foods, such as kelp and seaweed, can be consumed in life. In young patients with thickening of the isthmus and hypothyroidism, a small oral dose of levothyroxine sodium tablets can be considered to suppress the secretion of thyroid stimulating hormone in the anterior pituitary gland to relieve the thickening and enlargement of the isthmus. The usual dose should be started at a small dose, e.g. 25-50ug once daily, with regular review of thyroid function to adjust the drug dose. If the following conditions occur, surgery should be considered, such as thickening of the isthmus that compresses the trachea or esophagus, causing clinical symptoms such as dyspnea, pharyngeal discomfort, etc., or a large goiter that affects life and work, causing compression. The presence of nodules in the isthmus does not exclude malignancy and requires prompt surgical removal.