Endocrine Abstracts

Introduction

Pituitary adenomas secreting TSH (TSHoma) are a rare cause of hyperthyroidism. They account for approximately 0.5–3 % of functioning pituitary tumours and much less than 1% of all cases of hyperthyroidism. TSHoma should be considered in all hyperthyroid patients, especially those with diffuse goitre and no extrathyroidal signs of Graves’ disease.

Case 1

A 30-year-old female applied to the internal medicine department with complaints of palpitations, diarrhea, sweating and weight loss. In repeated examinations, high levels of TSH, fT3 and fT4 were detected, TSH, fT3 and fT4 values examined in 3 different centres and again found to be high.The serum sex hormone-binding globulin concentration was slightly elevated. In family screening, no thyroid dysfunction was detected. In pituitary MRI, 5 mm adenoma was detected.The serum α-subunit level was 2.4 ng/ml (normal < 1.2), and the α-subunit/TSH molar ratio (α-subunit × 10/TSH) was 4.3 (normal < 1).We performed an analysis for mutations in the THRB gene; no mutations found. The serum TSH concentration didn’t increase in response to the thyrotropin-releasing hormone, while a fall in serum TSH concentrations was detected in response to administered T3. Since the tests showed discordance, a short course of long-acting (LAR) somatostatin analogue (SSA) was administered. Thyroid function tests returned to normal with LAR-SSA therapy and strengthened the diagnosis of TSHoma. Surgery was planned.

Case 2

A 35-year-old male patient was referred to the endocrinology department when elevated TSH, fT3 and fT4 values were detected in the smoking cessation outpatient clinic. Repeated examinations in the same centre and two different centres showed high TSH, fT3 and fT4 levels. No thyroid dysfunction was found in first-degree relatives.The serum sex hormone-binding globulin concentration was normal, and the serum a-subunit level was 0.7 ng/ml (normal<0.5). In pituitary MRI, 7 mm adenoma was detected. The serum TSH concentration didn’t increase in response to the thyrotropin-releasing hormone, while a fall in serum TSH concentrations was detected in response to administered T3. Since the tests showed discordance, a short course of LAR-SSA was administered. Thyroid function tests returned to normal with LAR-SSA therapy and strengthened the diagnosis of TSHoma.Surgery was planned.

Conclusion

Most TSHomas are detected as pituitary macroadenomas. The presence of a microadenoma on MRI is not specific for a TSH-secreting tumour and can be seen as an incidental finding in 10 per cent of normal individuals. The rutin tests used for the differential diagnosis of TSHoma and Thyroid hormone resistance sometimes may be discordant. In such cases, performing the LAR-SSA test strengthen the diagnosis.