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Thyrotropinomas 

Thyrotropinomas
Chapter:
Thyrotropinomas
Author(s):

Paolo Beck-Peccoz

and Luca Persani

DOI:
10.1093/med/9780199235292.003.2164
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date: 11 December 2019

Thyrotropinomas are rare tumours, accounting for no more than 1% of all secreting or nonsecreting pituitary adenomas (1, 2). Since the prevalence of pituitary tumours in the general population is about 0.03%, 1–3 thyrotropinomas are expected to be seen per million people. The number of reported thyrotropinomas increased exponentially in the past years, as a consequence of the introduction of ultrasensitive immunometric assays for thyroid-stimulating hormone (TSH) as first-line test for evaluating thyroid function (1). Based on the finding of measurable serum TSH levels in the presence of elevated thyroid hormone concentrations, many patients previously thought to be affected with Graves’ disease or toxic nodular goitre could be correctly diagnosed as patients with central hyperthyroidism. In our opinion, this latter term is preferable to ‘inappropriate secretion of TSH’, as it more precisely reflects the pathophysiological events underlying such an unusual disorder, where the thyroid hormone negative feedback mechanism is clearly disrupted and TSH itself is responsible for the hyperstimulation of the thyroid gland and the consequent hypersecretion of thyroid hormones (Fig. 2.3.13.1).

Central hyperthyroidism is mainly due to autonomous TSH hypersecretion from a thyrotropinoma. However, signs and symptoms of hyperthyroidism along with biochemical findings similar to those found in thyrotropinoma, may be recorded in the minority of patients with resistance to thyroid hormones (RTH) (3, 4). This form of RTH is called pituitary RTH (PRTH), as the resistance to thyroid hormone action appears more severe at the pituitary than at the peripheral tissue level (see Fig. 2.3.13.1). The clinical importance of these rare entities is based on the diagnostic and therapeutic challenges they present. Failure to recognize these different disorders may result in undesirable consequences, such as improper thyroid ablation in patients with central hyperthyroidism or unnecessary pituitary surgery in patients with RTH. Conversely, early diagnosis and correct treatment of thyrotropinomas may prevent the occurrence of complications (visual defects by compression of the optic chiasm, hypopituitarism, etc.) and should improve the rate of cure.

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