Endocrine Abstracts

Introduction: TSH-secreting pituitary neuroendocrine tumor (TSH-PitNET) is the rarest pituitary tumors. Most TSH-PitNETs are secreting, with a biological profile of inappropriate TSH secretion (moderately elevated TSH, elevated FT3 and FT4).

Observation: We report the case of a 69-year-old patient, with a history of total thyroidectomy in 2014 for multinodular goiter, hospitalized for suspected levothyroxine pseudo-malabsorption. Despite doses above 2 µg of levothyrox, the TSH always remains high above 10 mIU/l with high FT4. Clinically the patient presents some signs of hyperthyroidism.

Discussion: The diagnosis of pseudo malabsorption is unlikely, despite constantly elevated peripheral hormones the TSH remains elevated. Faced with a biological profile associating elevated peripheral hormones with an unrestrained TSH, the main differential diagnoses are thyroid hormone resistance syndrome and TSH PitNET. The age, sex and level of clinical thyroid functional tests are similar in the two pathologies. Thyroid hormone resistance syndrome is eliminated by a normal preoperative assessment. Hypothalamic pituitary MRI showed a 7.5 mm right pituitary microadenoma. A somatostatin analog braking test at 90 mg/28day was performed, after 2 months of treatment, TSH decreased to 1 mIU/l with reduced doses of levothyrox. The diagnosis of TSH-PitNET is retained in our patient despite the normality of the preoperative assessment which can be explained by a cyclic secretion, or a lifting of inhibition already described in the literature.