Clinical data: A 73-year-old woman was referred for regular follow-up examination. She was treated for hypothyroidism for 17 years. Carotid Doppler examination was performed a month before the recent visit because of vertigo and a large hypoechogenic nodule was described in the right lobe.

Functional state: subclinical hypothyroidism on daily 100 microgram levothyroxine (TSH 8.59 mIU/L, FT4 12.1 pM/L).

Ultrasonography. Both lobes were composed of a central hypoechogenic part surrounded with an echonormal rim. Although this pattern resembles that of a large hypoechogenic nodule occupying almost the entire lobe, this is one of the characteristic presentations of Hashimoto's thyroiditis. In contrast with a nodule, the borders between the central hypoechogenic area and the surrounding echonormal rim are irregular.

Suggestion: to increase the dose of levothyroxine to daily 125 micrograms.