Thyrotropin-Producing Pituitary Adenomas

Abstract

Thyrotropin-producing pituitary adenomas are rare cause of hyperthyroidism and it compose about 0.5-3% of all functioning pituitary tumors. Diagnosis of thyrotropin-producing pituitary adenomas can be challenging because TSH concentrations can be normal with only elevated T4. As a result, patient would be simply treated as primary hyperthyroidism. The latency between onset of hyperthyroidism and diagnosis of pituitary adenoma was reported to be 4-6 years. Many patients had radioactive iodine treatment or thyroidectomy treatment for primary hyperthyroidism at the time of diagnosis. A 35-year-old male with history of intermittent FT4 elevation for the past 3 years presented at endocrine clinic for evaluation. Patient also had recent headache and dizziness. TSH was only marginally elevated once in the past 3 years. Alpha-subunit was found to be 2.6 ng/mL with negative heterophile antibody. MRI showed a 13.7 mm x 20.4mm x16.1mm sellar and suprasellar mass without cavernous sinus invasion but with chiasmal compression. Other pituitary hormone co-secretion was not found in this patient. Patient was treated with octreotide 20mg monthly for 3 month with normalization of T4 and size of the tumor also decreased on the medication. Patients was prepared for transsphenoidal surgery. Treatment for thyrotropin-producing pituitary adenomas is mainly surgery. However, medical therapy with somatostatin analogs does play an important part in terms of inducing euthyroid prior to surgery. There are also articles describing shrinkage of the tumor prior to surgery while on somatostatin analogs. There were also rare case reports of thyroid storm from thyrotropin-producing pituitary adenomas when patients were not treated with somatostatin analogs prior to surgery. The surgical outcome was determined by the size of the tumor. Transient hypothyroidism or hypopituitarism can happen after the surgery. However, it is more common in external beam radiotherapy or radiosurgery treatment. For thyrotropin-producing pituitary microadenomas, transsphenoidal surgery is the treatment of choice with high remission rate. In some difficult cases where octreotide was not controlling the hyperthyroidism, methimazole use in combination with octreotide after surgery was also documented in the literature. The idea of using somatostatin analogs as primary treatment of thyrotropin-producing pituitary adenomas due to the risk of hypopituitarism with transsphenoidal surgery was explored in some literature. But, no strong evidence of better outcome with medication treatment alone was found.