Thyrotropinoma in a 45-Year-Old Man Treated with a Somatostatin Analog

Introduction : Thyrotropinoma is a rare pituitary tumor characterized by clinical and laboratory hyperthyroidism with unsuppressed TSH. His treatment of choice is surgical, but in most cases a cure is not achieved. We present the case of a patient with a TSH-producing macroadenoma who started treatment with lanreotide in times of pandemic with adequate disease control.

Case Description : A 45-year-old man, who came to our service for the first time in July 2021, reported increasing headaches throughout this year, which at times have been severe. From an endocrine perspective, we noted long-standing discordant thyroid function tests. The first thyroid function tests that could be located date back to 2013 and found a TSH of 10 mU/L with a T4 of 17 pmol/L (NV: 7-17) and, later, a TSH of 7 mU/L with a T4 of 19 pmol/L and a T3 of 7.9 pmol/L (NV: 3.5-6). These tests were done before any thyroxine treatment. To complicate matters, He is positive for thyroid antibodies, and based on this and his elevated TSH, he was started on thyroxine that he had been taking for about five years before we met him. He denied any specific symptoms of hyperthyroidism, but had noticed some fatigue and exercise intolerance. When he arrived with us, he was taking 200 mcg of thyroxine per day, we indicated the suspension of thyroxine, he presented the following results: TSH 28.2 mU/L, FT4: 14.83 pmol/L.
Analytical: alpha subunit 6.58 IU/L (0-0.7); TRAb < 0.3 IU / L ( < 1.8); SHBG: 39 mmol/L (NV: 10-50); TRH test was compatible with thyrotropinoma; IGF-1, ACTH, cortisol, prolactin, FSH, LH and testosterone: normal. Thyroid ultrasound: heterogeneous parenchyma, two micronodules in the left lobe (TIRADS 3). Pituitary MRI: 24x16x14mm macroadenoma with contrast enhancement. His visual fields are within normal limits.
Considering the pandemic situation, surgery was deferred and treatment with lanreotide 90 mg was started. Currently, 3 months after starting lanreotide, he reports a decrease in headache and shows a decrease in thyroid hormones TSH: 7.5 mU/L and FT4: 9.99 pmol/L; alpha subunit: 2.1 IU/L; the MRI showed a decrease in tumor volume by 20%.

Discussion : Thyrotropinomas represent a rare cause of hyperthyroidism in less than 1% of total cases and less than 3% of all pituitary tumors. The differential diagnosis of thyrotropinoma must be made mainly with syndromes of pituitary resistance to thyroid hormones, with the confirmation of the existence of a pituitary mass by imaging techniques being the main data that establishes the diagnosis. Many works suggest the use of somatostatin analogues as first-line therapy for patients with TSH-omas, particularly for invasive macroadenomas, the response is manifested by the decrease in the levels of TSH, alpha-SU and the recovery of the euthyroid state in the most of the cases.