Endocrine Abstracts

Introduction: We describe the case of 35-year-old man in whom laboratory abnormalities in thyroid function were observed by chance.

Case report: For the first time, the patient was examined in the local Department of Internal Medicine because of pre-arthroscopy examination in March 2002. Low level of total thyroid hormones (T₃ 0.76 nmol/l and T₄ 48.0 nmol/l) was observed by chance, while TSH value was normal (2.37 mIU/l). The patient did not suffer from any clinical symptoms, and the ultrasound scan showed a normal finding. It was thought about the central hypothyroidism and the patient was sent to MR of hypophysis where no pathology was found. The thyroxine substitution of low doses (50 μg/day) was medicated. The hormonal substitution was gradually increased to doses of 200 μg thyroxine/day. To endocrine ambulance the patient was sent in December 2005 for the first time. A low level of TSH and high level of free thyroid hormones was found. The patient was without clinical symptoms. We examined the function of hypophysis and it was normal. We recommended to discontinue the substitution, and the next examination showed normal level of TSH, while the level of total thyroid hormones remained low.

Conclusion: We closed the case with the diagnosis of TBG-binding capacity defect where the production disorder is congenital. These are laboratory changes without clinical significance. The diagnosis was confirmed by the level of TBG which was undetectable.

In practice, it is necessary take this defect into account because of the potential development of hyperthyreosis factitia caused by prolonged medication of the thyroxin substitution where the congenital TBG production disorder was not recognized. In differential diagnosis, it is necessary to rule out the central hypothyroidism.