Long-term preoperative management of thyrotropin-secreting pituitary adenoma with octreotide

Thyrotropin (TSH)-secreting pituitary adenomas are the less frequent form of presentation of pituitary tumors. Selective transsphenoidal surgical resection of the tumor is the treatment of choice. Given that native somatostatin inhibits TSH secretion, treatment with somatostatin analogues has been recently employed in patients with unresectable tumors or after surgery. We report on the case of a 58 year-old man with a TSH-secreting pituitary adenoma who was treated with octreotide for long-term before neurosurgery. The patient was referred to us because of a pituitary mass on CT scanning. Hormonal evaluation resulted in hyperthyroidism with high serum TSH concentrations. Serum alpha subunit concentration was elevated and TSH response to exogenous TRH stimulation was absent. Magnetic resonance imaging of the hypothalamic-pituitary area confirmed the presence of a pituitary mass (2.0 by 1.8 by 1.7 cm). Acutely administered subcutaneous octreotide (100 microg) was followed by a reduction of the serum TSH concentrations. Therefore, the patient received octreotide, 100 microg three times daily for 12 months. At first month after beginning therapy serum TSH, free thyroxine, total triiodothyronine, and alpha subunit concentrations were normalized and persisted into the normal range for the next 11 months. On the other hand, a shrinkage of the tumor mass (1.6 by 1.7 by 1.4 cm) was noted after 6 months of octreotide therapy, however, its volume did not modify in the following next months. Then, the tumor was removed by transsphenoidal surgery and the diagnosis was confirmed by immunohistochemical staining. This case demonstrates that long-term treatment with octreotide gave rise to a normalization of the thyroid function and a reduction of the tumor volume before surgery. This clinical observation suggests that octreotide therapy might be useful in preparation for pituitary surgery in patients with TSH-secreting pituitary adenomas.