Endocrine Abstracts

Introduction: Thyrotropin (TSH) secreting pituitary adenomas (TSHomas) are very rare and account for less than 2% of all pituitary adenomas. They present with elevated levels of fT4 and normal to high levels of TSH. About 25% of TSHomas co-secrete other anterior pituitary hormones. Growth hormone (GH) is the most commonly co-secreted hormone, followed by prolactin (PRL) and gonadotropins. Herein, we report a case of pituitary adenoma with simultaneous secretion of TSH and GH.

Case presentation: A 58 year-old man, with complete atrioventricular block, was assessed for thyroid function and was found thyrotoxic [fT4: 38.4 (12.0–22.0 pmol/l)] with inappropriately normal levels of TSH [TSH: 3.51 (0.27–4.20 mIU/l)]. He was not in any medication affecting thyroid function or thyroid hormone tests. He was started on methimazole, underwent implantation of a heart pacemaker and then referred to our department. The patient showed no clinical signs of hyperthyroidism. MRI imaging revealed a macroadenoma with suprasellar extension, in contact with the optic chiasm but with unaffected visual fields. Further assessment of pituitary function was diagnostic of growth hormone (GH) hypersecretion: abnormal GH suppression on a 75 g oral glucose tolerance test (OGTT) (nadir GH=2.11 ng/ml) with increased IGF-1 levels (524 ng/ml; age and sex specific reference range 71–350). Corticotroph and gonadotroph pituitary reserve was normal. Further workup, following discontinuation of thyreostatic drugs, confirmed the diagnosis of TSHoma: increased a-subunit and blunted TSH response to TRH. Patient was diagnosed with TSH/GH co-secreting pituitary macroadenoma and was set to treatment with a somatostatin receptor analogue (SSA, Sandostatin LAR 30 mg/28 days) that rendered him euthyroid but failed to normalize IGF-1 after 6 months of follow up. Thus, he was referred for neurosurgical evaluation and under-went transsphenoidal resection of the adenoma. Histopathology showed tumor cells with abundant cytoplasmic positivity for GH and TSH on immunohistochemical staining. After surgery, thyroid hormone and IGF-1 levels were normalized and GH was normally suppressed on OGTT. Patient is now on complete biochemical remission, 10 months post-operatively.

Discussion: TSHoma is a rare pituitary tumor and GH co-secretion renders our case even more unusual. These tumors usually lack prominent clinical manifestations. An SSA managed to promptly control TSH hypersecretion, but not GH even after prolonged use. Complete biochemical remission was finally achieved with pituitary surgery.