Endocrine Abstracts

Introduction: High thyroid hormone levels with unsupressed TSH (atypical hyperthyroxinemia) is one of the difficult endocrinologic conditions. When the conditions leading to euthyroid hyperthyoxinism are excluded, TSH secreting pituitary adenomas (TSHoma) and thyroid hormone resistance beta syndrome (THRB) lead to this picture as rare diseases. This report aims to evaluate the diagnostic and therapeutic stages in the case of TSH-secreting pituitary microadenoma which response to cabergoline treatment.

Case: A 49-year-old male patient was evaluated three years ago for palpitations and sweating. TSH, fT3 and fT4 were found 1.0 μIU/ml (0.350–4.940), 5.2 pg/ml (1.71–3.71) and 1.84 ng/dl (0.70–1.48) respectevely. Patient subsequently losted from the follow-up. Because of the increase in complaints has been reevaluated two months ago and similar findings were found in the tests. Pituitary MRI showed a pituitary adenoma on the left side and 7×4 mm in-size. Atrial fibrillation was present in the clinic, SHBG level was 62 nmol/l (10–57). In the TRH stimulation test, TSH levels were 1.598, 5.43, 6.702, 6.081, 5.521 (considered non-diagnostic). Alpha subunit level was 1.49 ng/ml (≤ 0.5). Cabergoline treatment has been started to the patient because he has not tolerated short-acting sandostatin due to diarrhea. Genetic test result was negative for THRbeta. TSH levels were decreased from 1.39 to 0.86 and fT4 levels were decreased from 1.97 to 1.67. The patient’s complaints improved and then after make sure diagnosis of TSHoma he was referred to the neurosurgery.

Conclussion: In patients with atypical hyperthyroxinemia, a very good clinical evaluation should be performed for differential diagnosis between TSHoma and THRB. Negative family history/screening, high alpha subunit level, 5-fold increase in TSH after TRH stimulation, adenoma on MRI are features of TSH-secreting adenoma. However, hypophyseal hyperplasia can be seen in THRB, heterogeneity in clinical findings, genetic testing can not always be done or result is negative in 10% of patients with THRB, makes the differential diagnosis problematic. In patients diagnosed with TSHoma, the pathologic condition is often macroadenoma, but occasionally also microadenoma may occur. Surgical treatment is the main treatment option and long-acting somatostatin analogues are used effectively in patients who can not undergo surgery or who are not cured and for pre-surgery in some patients. The effect of cabergoline is more limited. However, it can be seen that if there are microadenomas and the clinical findings are milder, such as in our case, cabergoline may be considered a suitable option.