A Thyroid-stimulating Hormone (TSH) Producing Adenoma in a Patient with Severe Hypothyroidism: Thyroxine Replacement Reduced the TSH Level and Tumor Size.

We treated an extremely rare thyroid-stimulating hormone (TSH)-producing pituitary adenoma in a 63-year-old woman with severe hypothyroidism due to autoimmune thyroiditis. She was presented with dizziness and fatigue. The blood level of TSH, prolactin, and fT4 was 288.2 μIU/mL, 72.9 ng/mL, and 0.24 ng/dL, respectively. Magnetic resonance imaging demonstrated a large pituitary tumor, 31 mm in height, and a normal pituitary gland. Preoperative thyroxine replacement reduced the TSH level to 2.05 μIU/mL and produced a significant reduction in the tumor volume. Histopathologically, the surgically removed tumor was a TSH-producing pituitary adenoma.