Hashimoto's thyroiditis and severe hypothyroidism, associated with a single hot nodule

We report the case of a 27 year-old man with symptoms of severe hypothyroidism that have evolved since his adolescence. He was found to have an 11 mm right lobe thyroid nodule. On thyroid ultrasound, the nodule was solid, heterogeneous with markedly atrophic hypoechoic surrounding tissue. Thyroid scintigraphy revealed increased ^99mTc pertechnetate and ¹³¹I uptake, with persistence of ¹³¹I hyperfixation after 24 h. There was no fixation of the radiotracer in the remaining tissue. Thyroid function tests found TSH > 100 mIU/l, free thyroxine level 0.9 pmol/l (normal values 11.5-21.8), anti-thyroid peroxydase antibodies strongly positive > 1,000 IU/ml, and anti-thyroglobulin antibodies negative. One year after levothyroxine therapy, the nodule decreased to 40% of its original size.

Hashimoto's thyroiditis may present as a single hot nodule and severe hypothyroidism. Data of reported cases suggest that the hot nodule corresponds to a localized hyperplasia of the less diseased portions of the thyroid. Chronic stimulation by TSH may have promoted nodular growth and isotopes uptake.