Clinical data: a 51-year-old woman was referred for an evaluation of typical signs of hyperthyroidism lasting for 5 weeks. 4 months before present examination the patient was euthyroid with a TSH 0.71 mIU/L.

Palpation: an enlarged right thyroid with a nodule. The left lobe was not palpable.

Results of blood tests: hyperthyroidism with undetectable TSH-level. FT4 was 43.8 pM/L. TSAb-assay 8.2 U/l (normal value under 1.5).

Ultrasonography: a moderately hypoechogenic thyroid with increased vascularization was found. There was an echonormal nodule in the right lobe with combined type 2 and type 3 vascular pattern.

Aspiration cytology: from the nodule resulted in benign lesion corresponding to hyperthyroidism.

Scintigraphy:  indicated an autonomously functioning nodule.

The patient was treated with thyrostatic drugs. After the normalization of FT4-level, she was operated on.

Histopathology: diffuse goiter corresponding to Graves' disease. Normofollicular adenoma in the right thyroid.

Comment: the sudden development of a hyperthyroidism is an unusual phenomenon in the case of a toxic nodule except for excess iodine ingestion and in the case of a coexistent Graves' disease.