Endocrine Abstracts

Background: Thyroid stimulation hormone producing pituitary adenomas [TSHoma] are very rare and present a diagnostic and management challenge due to limited clinical guidance. Indolent presentations such as multinodular goiter and mild hyperthyroidism can easily mislead the management. Moreover, we would also like to emphasize limitations of TSH with a reflex free T4 [FT4] test in such scenarios.

Clinical Presentation: Forty-three years old female was experiencing mild hyperthyroid symptoms and progressively enlarging multinodular goiter for few years. She was advised to get thyroidectomy after biopsy proven benign nodules. Interestingly, free thyroid hormones were mildly higher than ULN of 19.8 pmol/l for FT4 and 6.8 pmo/l for free T3 over last 5 years with inadequate TSH suppression with TSH between 1.4-2.1 mIU/l. Presurgical CT neck showed incidental sellar mass with subsequent MRI showing a 1.8 cm pituitary adenoma invading the right cavernous sinus and almost encircling the right cavernous carotid. Additional biochemical work up including elevated alpha subunit 2.7 ng/ml, SHBG 194.5 nmol/l with high alpha subunit/TSH ratio strongly suggested TSHoma. Due to invasive nature of the tumour, we employed primary pharmacotherapy with somatostatin receptor ligand (SRL) which holds promising potential, with reported instances of tumour regression in ~ 40% of cases. She was treated with octreotide LAR 20 mg every 4 weeks with subsequent follow ups over last 6 months showing very significant clinical, biochemical and radiologic improvement in goiter and pituitary tumour. Thyroid hormone levels are completely normalized now with resolution of hyperthyroid symptoms. Six months follow up pituitary MRI shows pituitary adenoma size is significantly decreased from 1.8 cm to 1.1 cm with regression of invasion.

Conclusion: TSHoma compromise 0.5-3% of pituitary adenomas. Majority of the cases come to attention as sellar mass affect so high index of suspicion is warranted especially when presentation is more indolent. High free hormones with inadequate TSH suppression should raise suspicion also highlighting the limitations of TSH with reflex FT4 test employed at many practices. TSH remained completely normal during her clinical course. Trans-sphenoidal resection is the most common primary treatment, but primary pharmacotherapy with SRL is also employed in select cases with limited success. Patient preference, lack of chiasmal compression, Knosp 3B-4 cavernous sinus invasion with gross total resection unlikely and progressively enlarging multinodular goiter were the factors that guided us to resort to SRL as primary treatment. Subsequent significant improvement highlights the importance of considering such therapy in carefully selected patients.