Endocrine Abstracts

Introduction: Thyrotropin (TSH)-secreting pituitary adenomas are rare (<1% of all pituitary tumors) and cause secondary hyperthyroidism.

Case report: A 33-year old woman with type 1 diabetes mellitus presented in 2009 with palpitations. She had a past medical history of radioiodine therapy for thyrotoxicosis in 1998. After radioiodine treatment, she received an increasing daily dose of thyroxine (from 50 to 175 μg) because of her gradually rising serum TSH concentration.

Initial findings were: elevated serum TSH of 14.6 mIU/l (normal range: 0.27–4.2), elevated free-triiodothyronine (fT₃) concentration of 4.3 pg/ml (normal range: 1.64–3.45) and elevated free-thyroxine (fT₄) concentration of 1.87 ng/dl (normal range: 0.71–1.85). Thyroid antibodies were within normal ranges. After administration of 200 μg of thyrotropin-releasing hormone, TSH rose slightly from 24.9 to 31.26 mIU/l at 30 min. and to 29.14 mIU/l at 60 min. Alpha-subunit was 18 mIU/ml (normal range: 0.0–1.0). Other pituitary hormones and IGF1 were within normal ranges.

Magnetic resonance imaging (MRI) revealed a pituitary macroadenoma (13×12.5×10 mm) infiltrating the left cavernous sinus.

The patient was initially treated with octreotide-LAR (20 mg i.m. every 28 days) for ten months. During therapy serum TSH levels were reduced by more than 50%. No significant change in pituitary tumor volume was observed in MRI performed after octreotide-LAR treatment. In January 2011 the patient underwent uncomplicated transsphenoidal surgery, and immunohistochemical staining showed positive reactivity for TSH. Early postoperative TSH concentration was low (0.072 mIU/l) and became normal in 5 weeks. In subsequent months the patient remained euthyroid on 125 μg thyroxine daily. Pituitary MRI performed during one year follow-up did not reveal tumor recurrence.

Conclusions: We report for the first time the data on preoperative somatostatin analogue treatment of thyrotropinoma in a patient who previously underwent thyroid ablation by radioiodine. Since aggressive and invasive macroadenomas are more frequently observed in these patients, we suggest that preoperative treatment with somatostatin analogues should be mandatory in these patients.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.