Long-term follow-up of thyroid scintigraphies after 131I therapy of solitary autonomous thyroid nodules.

The aim of the present study was to assess thyroid scintigraphies after 131I treatment of autonomous thyroid nodules with respect to evolution of the hot nodules as well as the extranodular tissue. A 99mTc pertechnetate scintigraphy was carried out 1-16 years (median 8 years) after 131I treatment of a solitary autonomous nodule in 66 patients remaining euthyroid. At the time of diagnosis, 9 of the patients were euthyroid and 57 were hyperthyroid, of whom 27 received antithyroid drug therapy prior to 131I treatment. The scintigraphies were evaluated twice by 4 specialists (3 endocrinologists and 1 specialist in nuclear medicine). There was total agreement between the 4 observers in 50 and 52% in the first and second evaluation, respectively. The interobserver variation was evaluated by means of omega coefficients and omega ranged from 0.18 to 0.76 indicating poor to substantial agreement. A solitary autonomous nodule with suppression of the extranodular thyroid tissue persisted in 50% of the patients, whereas a solitary cold nodule, homogeneous uptake or inhomogeneous uptake was found in 15, 22, and 13%, respectively. We conclude that although euthyroidism is achieved by radioiodine treatment, a hot nodule suppressing the 99mTc pertechnetate in the extranodular tissue is still found in 50% of the patients even when serum TSH has been normal for years. Antithyroid drug therapy prior to 131I treatment was more frequent in this group of patients.