TSH-secreting (thyrotroph) adenomas are tumors of the pituitary gland that secrete thyroid-stimulating hormone (TSH), which causes excess production of thyroid hormones (T3 and T4) by the the thyroid gland – a condition known as hyperthyroidism. These tumors can also be associated with long-standing primary hypothyroidism. They are very rare and account for less than 1% of all pituitary tumors. TSH-secreting adenomas can simultaneously secrete other hormones including growth hormone, prolactinoma, and gonadotropins and tend to invade into nearby areas of the brain, such as the cavernous sinus. Most of these tumors are macroadenomas (tumors larger than 10 mm).
Common symptoms are the same as those seen with hyperthyroidism:
- weight loss
- heat intolerance
Large macroadenomas can also cause headaches and compress the optic nerves, leading to visual field disturbances. A goiter may be present. Some patients may have bulging or protruding of the eye on one side if the tumor has invaded the orbital cavity.
In blood tests, T4 and T3 levels are elevated in most patients. Serum TSH levels are either elevated or "inappropriately" normal. T3 administration does not usually suppress TSH secretion by these tumors. Imaging with CT or MRI can confirm the presence of a tumor.
Elevated T4 and T3 levels combined with elevated or normal TSH levels can also be a sign of central resistance to thyroid hormone. Central or pituitary resistance to thyroid hormone is a genetic disorder caused by a mutation in the T3 receptor in cells of the pituitary gland. Patients with central resistance to thyroid hormone do not have TSH-secreting adenomas.
Transsphenoidal surgery to remove the tumor is the primary treatment for TSH-secreting adenomas. If the tumor has invaded into the cavernous sinus and cannot be completely removed, patients may undergo radiosurgery or a trial of medical therapy with a somatostatin analog to treat any residual tumor. Therapy with somatostatin analogs can control TSH levels and normalize T4 and T3 levels in more than two thirds of patients. Antithyroid drugs, such as propylthiouracil or methimazole, can be used to control hyperthyroidism in some patients. Beta blockers can also be used to alleviate symptomatic hyperthyroidism while awaiting beneficial effects of other treatments.