TSH-secreting pituitary adenomas are benign tumours of the pituitary gland. They produce too much thyroid stimulating hormone (TSH), which causes the thyroid gland to enlarge and produce thyroid hormone in excess, leading to an overactive thyroid (hyperthyroidism). Patients typically present with signs and symptoms of hyperthyroidism, but these patients may also have headaches and loss of some of their field of vision; rarely, there are no symptoms (asymptomatic). Early diagnosis and correct treatment may prevent pituitary and heart complications and may improve cure rate.
The cause and the changes at a molecular level that might lead to the development of a TSH-secreting pituitary adenoma are currently unknown.
Patients may present with symptoms of hyperthyroidism including sweating, heat intolerance, shaky hands, palpitations, nervousness, increased stool frequency, weight loss, poor sleep quality, fatigue, and irregular periods. They may also present with headache, visual disturbance, an enlarged thyroid gland (goitre) and galactorrhoea (inappropriate milky discharge from the breasts).
TSH-secreting pituitary adenomas are rare tumours and account for less than 1% of all pituitary adenomas. Since the prevalence in the general population of all pituitary adenomas is estimated to be around 0.02%, TSH-secreting pituitary adenomas affect about one person per million over their lifetime. The average age of people affected is in their 40s and 50s.
Inherited cases of TSH-secreting pituitary adenomas have not been documented.
TSH-secreting pituitary adenomas are diagnosed by laboratory and radiological tests. Laboratory tests involve measuring blood thyroid hormone and thyroid stimulating hormone (TSH) levels. Further blood tests are taken to measure the levels of other hormones produced by the pituitary gland. Imaging of the pituitary is required to complete the diagnosis. Magnetic resonance imaging (MRI) or computerised tomography (CT) of the pituitary is used to image the pituitary and look for a mass. These tests are usually carried out as outpatient appointments.
Similar biochemical findings to the above tests may also be found in patients with a related condition called ‘resistance to thyroid hormone’ (see the article on resistance to thyroid hormone for further details).
The most common initial therapy for patients with a TSH-secreting pituitary adenoma is transphenoidal resection of the tumour. This is an operation whereby the tumour is removed via the nasal cavity. Transcranial (through the skull) resection of the tumour may be performed for very large tumours. Transphenoidal surgery generally requires 3–4 days in hospital, whereas transcranial surgery requires slightly longer, 5–7 days. Most surgery is performed routinely except in the case of rapidly deteriorating vision. If surgery is not advisable or does not work, radiation to the pituitary and/or medical treatment with somatostatin analogues (Octreotide, Laneotide) can be used.
Anti-thyroid therapy of any type such as radioiodine or anti-thyroid medications (e.g. carbimazole or propylthiouracil) are not used to treat patients with TSH-secreting pituitary adenomas as these would be expected to increase thyroid stimulating hormone secretion and stimulate tumour growth.
The surgery may cause the pituitary gland to under-function (hypopituitarism), either partially or completely. Assessment of pituitary function to measure the amount of hormones the pituitary is producing should be undertaken soon after surgery. Appropriate hormone replacement may be required. Patients on somatostatin analogues may also experience side-effects, particularly related to gastrointestinal disturbance, as well as gallstone formation and occasionally diabetes mellitus. Radiotherapy can lead to failure of the normal pituitary gland tissue over the following years, again resulting in hypopituitarism. Patients should discuss any concerns they have about possible side-effects of treatment with their doctor.
If left untreated, in addition to complications of hyperthyroidism, patients may experience neurological complications such as visual field defects, due to compression of the nerves to the eyes; hypopituitarism; decrease in sexual function; acromegaly, which can occur in a proportion of tumours that also produce growth hormone; and galacorrhoea, either due to compression of the pituitary stalk (which connects the pituitary gland to the brain), by the tumour, or by direct secretion of prolactin by the TSH-secreting pituitary adenoma.
Patients with long-term hypopituitarism as a result of surgery to remove the tumour will likely need to take daily medication for life and will require regular checks with an endocrinologist at an outpatient clinic to monitor pituitary and thyroid hormone levels.
Hypopituitarism is associated with an increased risk of heart disease and stroke. Therefore, healthy living, a balanced diet and taking exercise to prevent becoming overweight are essential to reduce this risk. Appropriate pituitary hormone replacement therapy can reduce all these risks.
Last reviewed: Jan 2015