TSH Producing Adenoma
A TSH-producing pituitary adenoma is one that makes too much of the hormone called “thyroid stimulating hormone.” Thyroid stimulating hormone stimulates the thyroid gland to produce the thyroid hormones (T4 and T3). These hormones regulate metabolism and affect the growth and rate of function of other organs. Continuous stimulation of the thyroid gland by TSH may cause an overactive thyroid gland (hyperthyroidism).
A TSH producing pituitary adenoma is the least common type of pituitary adenoma, occurring in only 1-3% of all pituitary adenomas. This type of tumor is more common in females. The tumors are often greater than 1 cm in diameter, referred to as a macroadenoma. Since this type of tumor affects multiple areas of the body, a multidisciplinary team including an endocrinologist, a neurosurgeon, an ophthalmologist and a radiologist is required to treat this tumor. With successful treatment hormone levels can return to normal and the tumor can be removed.
Symptoms of a TSH-producing tumor are related to overstimulation of the thyroid gland to produce too much thyroid hormone (hyperthyroidism).
Symptoms of hyperthyroidism include:
- Weight loss
- A fast heartbeat (palpitations)
- Tremor of the hands
- Difficulty sleeping
- Frequent bowel movements
- Less menstrual flow or loss of menstrual periods
Other symptoms of pituitary tumors are:
- Visual loss
A complete medical history and physical are first performed to determine if a patient’s symptoms indicate hyperthyroidism. Blood hormone levels of all pituitary hormones are measured.
A diagnosis is confirmed by:
- TSH and the thyroid hormone levels (T4 and T3) blood tests: In general, elevated T3 and/or T4 in the presence of normal or elevated TSH suggests a TSH-producing tumor. In some cases, thyroid hormones are normal despite the presence of a tumor. This is called a “silent TSH adenoma.”
- Imaging the pituitary by MRI or CT: Presence of a pituitary adenoma on the MRI study usually shows a large tumor; however, some tumors may be too small to see.
The usual treatment of a TSH adenoma is surgical removal. However, medical treatment with a medication called a somatostatin analog may be effective.
The goals of treatment are to:
- Restore production of TSH and thyroid hormones to normal
- Stop and reverse the symptoms of TSH-producing adenomas
- Correct other endocrine abnormalities (adrenal, ovaries or testes)
- Remove and/or destroy the tumor to restore endocrine function to normal and to relieve any symptoms directly related to the tumor (headaches, visual disturbance)
Medical treatment for this type of tumor is a somatostatin analog, Sandostatin LAR. This drug acts on the tumor to lower TSH production by the tumor which results in lowering of both TSH and thyroid hormone levels.
Some patients have a decrease in tumor size as well. Some patients have been treated successfully only with Sandostatin LAR (an injection in the buttock once a month) and have not required surgery. Sandostatin LAR does not destroy the tumor; it is only effective as long as it is administered, so it is not a cure.
Surgical removal is the more common form of treatment for TSH-producing adenomas and is done using a transphenoidal approach (the operation is performed through the nose without disturbing the brain or the eye nerves).
For TSH-producing tumors, medical treatment of the overactive thyroid gland is necessary before the operation in order to protect against heart problems (abnormal heart rhythm) during surgery. Medical treatment before surgery usually takes 3–4 weeks. The medications used include a “beta-blocker” like propranolol or metroprolol, which slows the heart rate, and methimazole, a drug that reduces the amount of thyroid hormone production.
After successful surgery
Complete surgical removal of the tumor results in normal thyroid hormone production. Although hormone levels will return to normal within days, the symptoms of a TSH producing adenoma may take days to weeks to resolve. In some patients, the TSH level may be very low after the surgery and the patient will require thyroid hormone replacement either temporarily or permanently. This needs to be reevaluated after surgery.
In patients who have persistent elevation of TSH despite medical therapy or who cannot receive medical therapy for one reason or another (often cost of medication), radiation therapy or radiosurgery are options. Conventional radiation therapy is effective, but does involve a 4-6 week period of treatment. Single treatment focused stereotactic radiosurgery, such as Gamma Knife, has been a successful option and also has the potential of providing excellent long-term control.
There are no known steps to prevent TSH-producing adenomas. Early diagnosis allows for tumors to be diagnosed when they are small, which improves the chance of cure with surgery alone. Early treatment prevents the progression of visual loss and headaches caused by many larger tumors.
A TSH producing pituitary adenoma can be treated effectively with surgical removal (depending on the size and location of the tumor) and with medication. Because any type of pituitary tumor may recur, regular follow up with blood tests is necessary and if the blood tests show a return of a high TSH and thyroid hormone levels, an MRI scan is necessary. If a recurrent tumor is found, additional treatment is necessary.