Unusual thyroid scintigrams in Plummer's disease during methimazole therapy. Conversion of hot to hypofunctional nodules.

Thyroid scintigrams of two women (aged 48 and 58) with Plummer's disease showed unusual radioiodine accumulation during treatment with methimazole (MMI). Before MMI therapy, the scintigrams revealed most of the radioiodine uptake only in the nodules of the patients and very little uptake in the non-nodular portions of the thyroid. After initiation of MMI therapy, scintigrams performed at three and eight months revealed that the hot nodules had become hypofunctional and that the surrounding tissues had normal radioiodine accumulation. The findings indicate that the nodules in Plummer's disease continue to concentrate MMI selectively compared with normal surrounding thyroid tissue during therapy.