[Inappropriate thyrotropin secretion. Part 1: tumoral (author's transl)]

Release of thyroxine and triiodothyronine from the thyroid gland is stimulated by the pituitary hormone thyrotropin, or thyroid-stimulating hormone (TSH). TSH secretion in turn is regulated by control mechanisms, which include a negative feedback effect of the thyroid hormones themselves and the actions of the hypothalamic peptide TRH and of several central neurotransmitters. Hyperthyroidism secondary to excessive TSH secretion is a rare entity. In most cases TSH hypersecretion results from an adenoma of the pituitary gland and may then be associated with increased prolactin or growth hormone production. It should be emphasized that most patients with pituitary adenoma have high serum levels of alpha TSH subunit and undetectable beta TSH subunit.