Clinical data: a 32-year-olda woman was referred for an evaluation of a mild hyperthyroidism. The hyperthyroidism was first detected during her pregnancy at thirty-third gestational week for 4 years ago. The TSH level was continuously < 0.01 mIU/L while the FT4 level was in the range of 25.1-32.8 pM/L. The patient had no specific sign of hyperthyroidism. The antibody tests (TSAb 3-times, while aTPO 4-times) were all negative. The patient did not ingest iodine. The pulse rate of the patient was 88/min, while her BMI was 24.8.

Palpation: no abnormality.

Results of blood tests: TSH 0.001 mIU/L, FT4 27.9 pM/L, TSAb and aTPO negative, CRP normal.

Scintigraphy: normal iodine uptake of the thyroid. Ectopic thyroid was not found.

Ultrasonography: the thyroids were echonormal without any discrete areas. The vascularization was decreased.

Cytology: was performed from the hypoechogenic lesion in the dorsal part of the right lobe.

Cytological diagnosis: benign pattern corresponding to Graves' hyperthyroidism.

We started with daily 10 mg methimazole.

Follow-up results: the patient was treated with methimazole for 6 months. 3 months after initiating the thyrostatic, subclinical hypothyroidism was observed and for this time we administered daily 10 mg methimazole and 50 microgram levo-tiroxin. 6 months after discontinuation of drugs the patient was euthyroid.

Comment: it is not an infrequent finding that a patient presents transient mild hyperthyroidism without any known reasons. In such events we suppose a failure of laboratory or a subclinical form of de Quervain's thyroiditis. However, this patient presented a continuous hyperthyroidism lasting for years which is a very unusual situation.

We do not know what was the cause for mild hyperthyroidism. Although it is conceivable that the thyroid was completely healthy, the pulse rate was elevated. Therefore it seems more likely that the patient had in fact a hyperthyroidism of autoimmune origin. Moreover, the cytological pattern presented signs of thyroid dysfunction at cellular level. Naturally, we cannot exclude the possibility that the patient ingested an unknown drug containing thyroid hormone, but she seemed to be psychologically stable and she denied to ingest any uncommon food or any drugs or multivitamins.