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

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.