SUN-294 - Diagnostic Challenge in Suspecting TSH-Oma

Introduction:
Thyrotropin-secreting pituitary tumors (TSHomas) account for only 1 % of all pituitary adenomas. Consideration of different types of analytical interference, including biotin heterophil antibody, and genetic disorders of thyroid hormone resistance, needs to be taken. The absence of a mass lesion on conventional imaging makes it further challenging.


Case description:
A 65-year-old female with a past medical history significant for thyroid cancer, referred to us for evaluation of elevated free T4 and TSH level. The patient wants to establish new care with us due to proximity. She was diagnosed with multicentric papillary thyroid cancer in 2001, followed by right hemithyroidectomy and later completed thyroidectomy in 2002. As per the surgery, margins were involved. In November 2002, she received 29 mCi of RAI, WBS showing uptake in the thyroid bed. No evidence of recurrence biochemically and structurally. Her thyroid replacement dose has resulted in suppressed TSH from 2009 till May 2021. Since October 2024, her free T4 levels were elevated 1.8 ng/dl with inappropriately normal TSH of 1.62 ulU/ml. Repeat analysis on June 2025 showed the same free T4 level and further elevation of TSH 2.78 ulU/ml, total T4 found to be upper normal 11.5 ug/dl, free T4 levels done via equilibrium dialysis also returned high at 2.4 (reference range 0.9-2.2). She has been taking levothyroxine 100 ugm daily appropriately. She was complaining about brain fog, menopausal symptoms of low libido, dyspareunia, and difficulty concentrating. During our encounter in October 2025, pituitary functions lab testing showed normal cortisol, ACTH, prolactin, elevated LH, and FSH levels. TSH was found to be 3.15 ulU/ml, alpha subunit found to be 0.4 ng/ml, with alpha subunit molar ratio found to be minimally elevated, 1.29%. HAMA treatment TSH measurement (3.43 mIU/l) corresponds with the conventional assay. Her mother has a history of hypothyroidism. MRI of the brain and CT head were negative for pituitary mass.


Discussion: Patients with elevated free T4 along with genuinely non-suppressed TSH, elevated alpha subunit molar ratio, despite negative imaging of pituitary adenoma, warrant further testing. Due to the unavailability of TRH suppression testing in the United State, our plan is to proceed with T3 suppression test, somatostatin suppression test, and special imaging (Met-PET co-registered with FSPGR MRI) to localize pituitary TSH-oma on subsequently.

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