A case of Plummer disease treated with radioactive iodine was described. A 74-year-old woman was examined for her thyroid mass, which had been unattended for 7 years, and was diagnosed as having Plummer disease. Laboratory tests showed high and low levels of thyroid hormones and TSH, respectively, but no clinical manifestation of hyperthyroidism
was observed. Technetium 99m scintigraphy showed strong accumulation to the mass and
suppressed accumulation to the normal part of the thyroid. Ultrasonography revealed apparent cystic change but no calcification. Malignancy of the lesion was excluded by cytological examination. The patient was administered 481 MBq of radioactive iodine 131 without restriction of iodine intake before the treatment. The hormone levels have been
normalized in one after treatment, and abnormal intake of the radioisotope into the lesion has been normalized. Amongst possible treatments for the disease, radioiodine therapy, but not radical surgery, was chosen based on the patient’s wishes.