Thyrotropin-Secreting Pituitary Adenoma: A Case Report

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We report a 44-year-old male with a thyrotropin (TSH)-secreting pituitary adenoma. Basal serum free triiodothyronine (FT3, 12.1pmol/l) and free thyroxine (FT4, 28 pmol/l) were increased with normal basal TSH (3.1mU/l). There was impaired TSH response to thyrotropin releasing hormone (TRH) test. Serum TSH was suppressed to 59% of the basal level after oral administration of 1.4mg 3, 3-5-triiodothyroacetic acid (triac), whereas no suppression was observed after 75 μg daily administration of triiodothyronine (T3). Serum concentrations of a-subunit of TSH (TSH-α) and TSH-α/TSH molar ratio were high, being 1.95μg/l, and 4.4, respectively. Pituitary CT and MRI scan showed the presence of a macroadenoma in the anterior lobe of the pituitary gland. Histopathology of the excised pituitary confirmed the diagnosis of a TSH-producing adenoma. A positive correlation between TSH and FT3 (r=0.66, P<0.01) or FT4 (r=0.54, P<0.01) was observed in serial sera obtained before and after operation.