Hyperthyroidism is mainly due to autoimmune thyroid disorders or toxic goiter, and very rarely to the presence of thyrotropin (TSH)-secreting pituitary adenomas (TSHomas). These tumors are characterized by high levels of circulating free thyroid hormones (FT4 and FT3) in the presence of nonsuppressed serum TSH concentrations. Failure to correctly diagnose TSHomas may result in inappropriate thyroid ablation, which results in a significant increase of pituitary tumor mass. The diagnosis is mainly achieved by measuring TSH after T3 suppression and TRH stimulation tests. These dynamic tests, together with pituitary imaging and genetic testing are useful in distinguishing TSHomas from the syndromes of resistance to thyroid hormone action. The treatment of choice is surgery. In cases of surgical failure, somatostatin analogs have been found to be effective in normalizing TSH secretion in more than 90% of patients.
Keywords: Central hyperthyroidism; Resistance to thyroid hormones; Somatostatin analogs; Thyrotropin; Thyrotropin-secreting pituitary adenoma; Transsphenoidal surgery.