MON-074 A Rare Case of Co-secretion of TSH and GH from a Pituitary Adenoma with Concurrent Differentiated Thyroid Cancer

Abstract Disclosure: Q.F. de Leon: None. F.P. Salvador-Badilles: None. K. Tolentino: None. P.D. Maningat: None. Background: Thyrotropin-secreting pituitary adenoma is the rarest type of functioning pituitary adenoma with co-secretion of growth hormone (GH) being the most common associated endocrinopathy. To date, this is the first reported case of TSH/GH-producing adenoma co-existing with differentiated thyroid cancer (DTC) in the Philippines and fourth globally. Clinical Case: A 65-year-old female with history of multiple thyroid surgeries presented with recurrent thyroid nodules, thyrotoxicosis and acromegaly features. Diagnostics showed persistently elevated FT4 and FT3 with non-suppressed TSH (without thyroid hormone replacement), elevated IGF-1 and positive growth hormone suppression test. Imaging revealed a pituitary macroadenoma (1.6 x 1.2 x 1.3 cm) without compression effects and a large neck mass (4.6 x 6.8 x 8.7 cm) causing tracheal displacement. Despite lacking access to genetic testing for thyroid hormone resistance, clinical features alongside biochemical findings and imaging suggested TSH/GH-producing pituitary adenoma. A surgical dilemma arose as to whether thyroid or pituitary surgery should be prioritized. Given the possibility of thyroid malignancy based on the history of recurrent and rapidly enlarging neck mass despite benign findings on biopsy, thyroid surgery was done with preoperative Methimazole treatment to achieve euthyroid state. Histopathological findings of papillary thyroid carcinoma (1.3 cm, TNM stage 1, low recurrence risk) further complicated management. Due to its rare occurrence, there is no consensus regarding the management of TSH/GH-producing pituitary adenoma co-existing with DTC. Recommendations to reduce serum TSH to prevent tumor recurrence may be challenging in patients with TSHoma due to persistent TSH secretion. Postoperatively, Levothyroxine was started but TSH suppression was inadequate. Due to the patient’s age and low recurrence risk with high-normal FT4 levels, we are reluctant to increase the Levothyroxine dose. Preoperative use of somatostatin receptor ligand (SRL) is crucial in controlling thyroid hormone levels, reducing tumor size, lowering IGF-1 and minimizing surgical risks in patients with severe comorbidities (pharyngeal thickening, severe OSA, heart failure). Pituitary surgery was delayed due to difficult intubation during the initial surgery. Given elevated thyroglobulin on follow-up, we plan to address the DTC with surgery or radioactive iodine (RAI) if surgery is not feasible. Post-RAI, SRL will be initiated to lower IGF-1 and TSH while awaiting pituitary surgery. Conclusion: Recurrent thyroid nodules despite multiple surgeries may indicate an underlying pituitary pathology, necessitating surgery as primary treatment with medical options like SRLs. The co-existence of a DTC complicates management requiring individualized treatment to optimize outcomes. Presentation: Monday, July 14, 2025