[Coexistence of resistance to thyroid hormone with pituitary incidentaloma]

Contrary to generalized resistance, pituitary resistance to thyroid hormones is characterized by features of hyperthyroidism. Its clinical manifestation resembles that of thyrotropin (TSH)-secreting adenomas, tumors constituting about 1-2% of all pituitary lesions. Both patients with resistance to thyroid hormone and thyrotropin-secreting tumors have increased plasma thyroid hormone levels and raised or inappropriately normal thyrotropin levels. However, their treatment is different and therefore differentiation of these entities is very important. The significant progress made in recent years in the field of high-resolution imaging procedures led to a situation during which hormonally inactive adenomas not posing a risk to a patient's health, referred to as incidentalomas, are discovered in endocrine organs including the pituitary. In our paper, we report a case of a young man with predominant pituitary resistance to thyroid hormone. Because of coexisting pituitary incidentaloma the patient was initially misdiagnosed as having a TSH-secreting tumor. We describe in details diagnostic and treatment strategies applied in our patient. The described case of our patient illustrates the need for clinical awareness of the possible presence of resistance to thyroid hormones in subjects with central hyperthyroidism and focal lesions in the pituitary.