Central Hyperthyroidism

Abstract

Central hyperthyroidism is a rare condition in which thyrotoxicosis results from primary overproduction of TSH by the pituitary gland with subsequent thyroid enlargement and hyperfunction. The two known causes of central hyperthyroidism are TSH-producing pituitary tumors (TSHomas) and the syndrome of PRTH. Both of these entities are characterized by clinical thyrotoxicosis, diffuse goiters, elevated circulating levels of free T4 and T3, and a nonsuppressed serum TSH. It is critical to distinguish central hyperthyroidism from the much more common types of primary hyperthyroidism, all of which have undetectable TSH values. TSHomas and PRTH can usually be differentiated from one another by measuring the serum alpha-subunit and the TSH response to intravenous TRH or exogenous thyroid hormone, and by pituitary imaging studies. TSHomas are usually benign adenomas arising from the monoclonal expansion of neoplastic thyrotropes. Causative oncogenes have not yet been convincingly identified. PRTH is a nonneoplastic disorder caused by inherited mutations in the gene for the thyroid hormone receptor beta; it is a poorly understood variant of GRTH. For unclear reasons, in PRTH, the pituitary gland is resistant to the feedback inhibitory effects of circulating thyroid hormones while peripheral tissues respond normally, causing patients to experience the toxic peripheral effects of thyroid hormone excess. TSHomas are best treated by transphenoidal surgical removal. Radiotherapy is indicated for inoperable or incompletely resected tumors. Octreotide administration is a useful adjunct for preoperatively reducing tumor size and for the medical management of surgical treatment failures. PRTH is ideally treated by chronically suppressing TSH secretion with medications such as D-thyroxine, TRIAC, octreotide, or bromocriptine. If such therapy is ineffective or unavailable, thyroid ablation with radioiodine or surgery may be employed with subsequent close monitoring of both thyroid hormone status and pituitary gland size.

Normal Delivery Following an Uneventful Pregnancy in a Japanese Acromegalic Patient after Discontinuation of Octreotide Long Acting Release Formulation at an Early Phase of Pregnancy

“…It is an established treatment option in acromegaly and in a variety of other clinical conditions such as TSH-secreting pituitary adenomas, pancreatic islet-cell tumors and carcinoid tumors [1][2][3][4]. In recent years a long-acting sustained-release formulation of octreotide (octreotide LAR) has been developed, which contains octreotide in a biodegradable polymer complex [5].…”

Inappropriate Secretion of Thyroid Stimulating Hormone in a Filipino Patient with a Pituitary Macroadenoma

“…Unlike patients with TSHomas, patients with RTH do not have symptoms of pituitary enlargement. 9 Reported cases of TSHomas have been macroadenomas in 90%. 10 Our patient has a pituitary macroadenoma associated with symptoms of pituitary enlargement.…”

Maternal-Fetal Thyroid Interactions

“…Close monitoring of the fetus is, therefore, strictly recommended, even in mothers treated by thyroidectomy before pregnancy but have still elevated TSAbs [142]. Taken together, there are two known causes of central hyperthyroidism [1,146]; (1) TSHproducing pituitary tumors (TSHomas) and (2) the syndrome of pituitary resistance to thyroid hormone (PRTH). In general, thyrotoxicosis is the syndrome resulting from an excess of circulating free T4 and/or free T3 [147,148].…”