Clinical presentation: A 39-year-old man has been treated for hyperthyroidism for 6 months by methimazole. Neither the TSAb nor the aTPO level was increased. He noticed fatigue and 7 kg weight gain in the previous weeks.

Palpation: a firm nodule in the right lobe.

Laboratory tests: TSH 0.04 mIU/L, FT4 5.53 pM/L, FT3 2.29 pM/L on daily 10 mg methimazole.

Ultrasonography. The thyroid was echonormal. There were several hypoechoic areas in the right lobe. The largest one in the upper ventrolateral part was deeply hypoechoic, presented taller-than-wide shape and had both blurred and lobulated margins.

Cytology was repeatedly non-diagnostic.

Suggestion: Considering the ultrasound presentation, the suspicion of papillary carcinoma was raised and surgery was advised.

Histopathology disclosed papillary carcinoma.