Endocrine Abstracts

JOINT1532

Background: TSHomas are rare pituitary tumors with an incidence of approximately 1 per million, accounting for 0.5% to 3% of pituitary adenomas. They present significant diagnostic and management challenges.

Case Presentation: A 51-year-old woman with a history of pulmonary embolism, hypertension and hypothyroidism on levothyroxine (LT4) with no regular follow-up, on her preoperative evaluation for an ovarian cyst removal had elevated TSH and free T4 (fT4) levels and was referred to our center for further evaluation. LT4 was discontinued and six weeks later the patient was clinically hyperthyroid with a TSH: 8.3 (0.27-4.20) mU/l, fT4: 5.3 (0.93-1.70) ng/dI, fT3: 11.2 (2.0-4.4) pg/mI. Her sex hormone-binding globulin was raised (SHBG >19 μg/mlæ upper normal limit 10.5) and the rest of her pituitary function was within normal range. Thyroid ultrasound revealed no goiter and there was no family history of thyroid disease. Due to technical and financial constraints, serum alpha subunit measurements were not performed. After assay interference was excluded, dynamic endocrine testing was conducted. The TSH response to TRH stimulation (200 μg TRH intravenously, with TSH measured at baseline, 20, 30, and 60 minutes) was blunted: baseline TSH 12.9 mU/l, peak TSH 17.9 mU/lan increase of 1.4-fold. A T3 suppression test (100 μg of liothyronine daily divided into four doses over 10 days; 25 μgX4) showed no suppression of TSH (TSH 8.4 mU/lafter T3-test.) SHBG levels remained elevated. The findings of these tests were indicative of a TSHoma and therefore the patient had a pituitary MRI which revealed a 17 mm×11 mm×10 mm suprasellar pituitary macroadenoma. A long-acting somatostatin analog therapy (octreotide LAR 20 mg every 28 days) was initiated and her TSH and fT4 levels dropped within the normal ranges (2.4 mU/land 1.3 pmol/lrespectively).

Conclusion: TSHomas typically present with elevated free thyroid hormone levels and inadequate TSH suppression or are incidentally discovered as sellar masses. The diagnostic approach involves biochemical evaluation (including SHBG, and serum alpha subunit), dynamic testing (TRH stimulation and T3 suppression tests), and often a short course of long-acting somatostatin analog therapy. Pituitary MRI typically reveals findings consistent with an adenoma. While transsphenoidal resection remains the treatment of choice, pharmacotherapy with long-acting somatostatin analog treatment may also be appropriate in selected cases. Factors such as patient preference, absence of chiasm compression, and cavernous sinus invasion (Knosp grade 3B-4) with a low likelihood of gross total resection influence the final decision for treatment.