Thyrotropin-secreting pituitary adenoma

Thyrotropin (TSH)-secreting pituitary adenoma (TSPA) is a rare cause of hyperthyroidism and detailed reports of this entity in Taiwan are uncommon. We report a patient with TSPA with symptoms of hyperthyroidism and describe the presentation, endocrine and histologic findings, and treatment. The patient, a 42-year-old man, presented with a 2-year history of weight loss, palpitation, anxiety, and bad temper. He had increased basal serum thyroxine (T4, 18.3 micrograms/dL) and triiodothyronine (T3, 250 ng/dL) concentrations. The TSH concentration was normal (4.6 microIU/mL) and showed impaired response to stimulation by TSH-releasing hormone. Tests for antithyroid antibodies were negative. Thyroid scintigraphy showed mild thyroid enlargement. The thyroid uptake of radioactive iodine (131I) was high at 2 hours (34%) and 24 hours (63%) after 131I administration. Other serum hormone concentrations were within normal limits. Magnetic resonance imaging of the brain showed a microadenoma in the pituitary region. Octreotide and bromocriptine tests showed 78.4% and 58.3% inhibition of TSH, respectively. The patient underwent trans-sphenoidal pituitary tumor excision, and the symptoms of hyperthyroidism subsided after surgery. Six months after the operation, there was no evidence of recurrence of the tumor or symptoms of hyperthyroidism. Hormonal supplements were also not necessary. In conclusion, TSPA is a rare cause of hyperthyroidism. However, in patients with symptoms of hyperthyroidism and increased basal serum T1 and T3 concentrations, but normal or even elevated serum TSH concentrations, TSPA should be considered in the differential diagnosis.