Thyroid-Stimulating Hormone (TSH)-Secreting Pituitary Macroadenoma Presenting as Biochemical Hyperthyroidism Without Clinical Symptoms: A Case Report

Thyroid-stimulating hormone (TSH)-secreting pituitary adenomas (TSH-omas) are a rare cause of hyperthyroidism. We present a case of a 46-year-old male who was incidentally diagnosed with hyperthyroidism during an annual physical examination, with elevated TSH and free T4 consistent with central hyperthyroidism. Diagnosis of TSH-oma requires a combination of biochemical testing, including measurement of the alpha subunit and the alpha-subunit/TSH molar ratio, pituitary imaging, and differential diagnosis to exclude resistance to thyroid hormone (RTH). Further evaluation for the patient confirmed an elevated alpha subunit and a ratio supportive of TSH-oma. A pituitary MRI revealed a pituitary macroadenoma. Surgery is the primary treatment modality, and the patient underwent successful endoscopic endonasal removal of the pituitary macroadenoma. Postoperative biochemical testing six weeks after surgery showed normalization of thyroid function.