Endocrine Abstracts

Case History: A thirty year old female presented to hospital after a first seizure. She had no significant past medical history. She had a one week history of recurrent frontal headaches and had noticed irregular periods. There were no clinical features of acromegaly. CT and MRI brain imaging showed a 5 cm mass arising from the pituitary fossa, extending into the suprasellar cistern and anterior cranial fossa. There was evidence of mass effect on the optic nerves and optic chiasm with oedema and mass effect affecting the right inferior frontal lobe.

Investigations: Blood tests showed a raised fT3 (13.6 pmol/L), raised fT4 (41.0 pmol/L) and elevated TSH (5.48 mu/L). These results were corroborated by a separate assay. The SHBG was normal at 115 nmol/L. The alpha-glycoprotein hormone subunit was elevated at 2.42 Iu/L. Prolactin was elevated at 963 miu/L. LH (10.3 iu/L), FSH (9.2 iu/L), GH (3.9 ug/L), cortisol (231 nmol/L), calcium (2.37 mmol/L) and PTH (1.92 pmol/L) were all in the normal range. IGF-1 was raised at 61.2 nmol/L. Short synacthen test caused serum cortisol level to rise to 447 mmol/L at one hour from a baseline of 240 mmol/L. These investigations were highly suggestive of a TSH-secreting macroadenoma.

Results and treatment: The patient was discharged on hydrocortisone, propranolol, carbimazole and levetiracetam. She returned to receive her first dose of octreotide 20 mg. Within one week, her thyroid function had normalised. Once euthyroid, the neurosurgical plan was for a multi-stage operation to remove the tumour. She underwent trans-sphenoidal surgery to remove the intra-sellar portion and frontal craniotomy one week later to remove the supra-sellar component. Histology has confirmed pituitary adenoma with focal TSH and GH expression. During surgery it was impossible to fully remove the tumour and subsequently her TSH and fT3/fT4 have risen. Post-operative imaging shows full resection of the sella component but remaining suprasellar tumour. She has received two further doses of octreotide to normalise her thyroid function prior to further surgery later this month.

Conclusions and points for discussion: TSH-secreting pituitary adenomas are rare, with an estimated incidence of one per million. They tend to present due to mass effect rather than hyperthyroidism as the patient gradually becomes accustomed to elevated thyroid hormone levels. This case exemplifies this as the presentation was with a seizure. This case demonstrates successful use of octreotide to normalise thyroid status prior to surgery, the complexity of surgery for large macroadenomas, and the atypical presentation of TSH-omas.