Hypothyroid Hashimoto’s thyroiditis (HT) with scintigraphic and acho-color doppler features mimicking autonomous adenoma.

A 48-years-old women on L-thyroxine (L-T4) therapy (100 g/day) for primary autoimmune hypothyroidism, diagnosed 15 years before, was seen in the outpatient clinic. She had a firm oval lump in the right thyroid lobe and symptoms of mild thyrotoxicosis. Serum free thyroid hormone were in the upper limit of normal range and TSH <0.01 mU/L by ultrasensitive assay. High titres of anti-thyroperoxidase, anti-thyroglobulin and anti-thyroid microsomal antibodies were detected. Thyroid ultrasonography (US) and colour flow doppler sonography (CFDS) revealed a voluminous hypoechoic hypervascularized nodule with increased peak systolic velocity (type III pattern) in the right lobe, with atrophic and hypoechoic extranodular tissue. An autonomous functioning nodule associated to HT was suspected, L-T4 therapy was temporary withdrawn, and the patient re-evaluated 2 months later. Off L-T4 therapy, thyroid function tests revealed marked primary hypothyroidism, while thyroid US and CFDS were unchanged. 99mTc thyroid scan showed a “hot” nodule in the right lobe with nearly absent uptake in the remaining thyroid tissue. In contrast, 131I scan displayed only faint patchy distribution, with very low uptake. Cytological examination revealed normal follicular cells and several lymphocytes. The final diagnosis was therefore hypothyroid HT with pseudo-nodular thyroid tissue of the right lobe. This is to our knowledge the first report of HT mimicking both scintigraphic and CFDS features of an autonomous functioning nodule.