Thyroid-Stimulating Hormone-Secreting Pituitary Adenoma: Two Cases With Challenging Diagnosis and Management

Abstract

Background: Thyroid-stimulating hormone (TSH)-secreting pituitary adenomas (TSHomas) are very rare pituitary tumors causing central hyperthyroidism. Most are macroadenomas (≥ 10 mm) with local and systemic comorbidities at diagnosis. The atypical changes in thyroid function tests (TFTs) may be subtle and are often initially missed, while over-secretion of other pituitary hormones is often present. Somatostatin analogs (SSAs) are the recommended first-line medical therapy for these lesions. We report two cases of TSHomas successfully managed with a dopamine agonist (DA) therapy, alone or following transsphenoidal surgery (TSS). Case Presentation: A 47-year-old man presented with significant weight loss, fatigue, and muscle weakness. He was found to have hyperprolactinemia, secondary adrenal insufficiency (AI), and central hypogonadism, which led to the discovery of a 3 cm invasive pituitary adenoma. Additional tests showed an increased IGF1, TSH, and free T4. A Pit-1 multihormonal tumor was documented on pathology after partial resection by TSS. Persistent hyperprolactinemia and central hyperthyroidism responded to DA therapy, as the patient refused therapy. A 66-year-old man with a history of anxiety, hypertension, coronary artery disease, atrial fibrillation, and thyroid nodules, was consulted for severe dizziness and was found to have a 2.4 cm pituitary adenoma on a head CT scan. Lab records showed a progressive supranormal free T4 and TSH increase over the preceding five years. He refused surgery and had an excellent clinical and biochemical response to DA treatment. Conclusion: Prompt detection of central hyperthyroidism by monitoring and correctly interpreting TFT over time is essential for early diagnosis and optimal management of TSHomas. TSH-secreting adenomas may respond to DA therapy.

Figure 1

Case 1: (A, C) Coronal and (B, D) sagittal postgadolinium T1-MR images of the pituitary macroadenoma with extension to the cavernous sinus (arrows), in 2017 (A, B) before transsphenoidal surgery and in 2019 (C, D) two years after surgery. Note the significant reduction in tumor mass with residual tumor mainly in the right cavernous sinus (larger arrowhead in C).

Figure 2

Case 2: (A, C) Coronal and (B, D) sagittal T1-FSE MRI selected images, (A, B) pretreatment in 2019 and (C, D) after cabergoline therapy in 2022. Tumor dimensions pretreatment were 2.18 cm × 2.38 cm × 2.17 cm vs. 1.71 cm × 0.96 cm × 2.02 cm during treatment.