Coexistence of an autonomously functioning thyroid nodule in a patient with Graves' disease: an unusual presentation of Marine-Lenhart syndrome.

A 44-year-old woman developed hyperthyroidism due to the coexistence of Graves' disease and an autonomously functioning thyroid nodule (AFTN). Anti-thyrotropin receptor antibody (TRAb) was strongly positive (83.2%), and a thyroid scan initially showed diffuse uptake of Tc-99m pertechnatate in both lobes and further increased uptake in accordance with the right lobe nodule. The nodule in the right lobe was histologically diagnosed as thyroid follicular adenoma. After she was maintained in a euthyroid state by treatment with Methymazole (MMI), thyroid uptake of Tc-99m in the nodule became lower and was slightly suppressed by T3 administrations probably due to its dependence on TSH. Subtotal thyroidectomy was performed and she subsequently became euthyroid with negative TBII activity. It is concluded that she had a coexisting functioning nodule with Graves' disease (Marine-Lenhart syndrome) and that the nodule changed from hot to cool along with the anti-thyroid treatment, unlike usual cases of this syndrome showing a cold nodule on the initial imaging under the hyperthyroid state. Repeated Tc-99m pertechnatate thyroid scans were helpful in evaluating the reaction of MMI and TSH in both lesions separately in the present case.