THYROID HYPOECHOGENICITY AFTER METHIMAZOLE WITHDRAWAL IN GRAVES-DISEASE - A USEFUL INDEX FOR PREDICTING RECURRENCE

OBJECTIVE A characteristic thyroid ultrasonographic picture with diffu se or scattered low echogenicity has been described in Graves' disease (GD). Thyroid hypoechogenicity in GD at onset has been considered a p rognostic index of relapse after medical treatment; moreover, thyroid hypoechogenicity is regularly observed in GD at the onset, but not in patients with 'burned-out' disease. The aim of this study was to evalu ate the usefulness of thyroid hypoechogenicity changes in predicting G D relapse. DESIGN Longitudinal prospective study of previously untreat ed patients with GD. PATIENTS Thirty-nine consecutive patients aged 10 -72 years were treated with methimazole (MMI) for 12-24 months on a ti tration regimen. Evaluation of patients in remission or with relapse w as done 12 and 24 months after MMI withdrawal. MEASUREMENTS Thyroid ul trasonography and TSH receptor antibodies (TRAb) were evaluated in bas al conditions and then one month after MMI withdrawal. Thyroid hypoech ogenicity score (assessed by the same observer with the same equipment ) was graded as: 0 absent; 1 mild; 2 moderate; 3 marked. At the withdr awal evaluation a score < 2 and a TRAb value < 10 U/l were considered as normal. RESULTS Twelve and 24 months after withdrawal, there were 1 0 (25.6%) and 17 (44.7%) relapses, respectively. Neither thyroid hypoe chogenicity score nor TRAb values evaluated in basal conditions, showe d significant differences between patients remaining euthyroid and tho se who became again hyperthyroid. In the whole group, the thyroid hypo echogenicity score was significantly lower at the withdrawal than in b asal conditions (1.1+/-1.1 vs 2+/-0.8; P < 0.0001); it was significant ly lower in patients in remission (P < 0.001), but not in those who re lapsed. The thyroid hypoechogenicity score at withdrawal was normal in 23/29 (79.3%) of patients still euthyroid and in 4/10 (40%) of those who relapsed up to the 12th month (P < 0.05); it was normal in 19/21 ( 90.4%) of patients still euthyroid and in 7/17 (41.2%) of those who re lapsed up to the 24th month (P < 0.05). A normal thyroid hypoechogenic ity score at withdrawal of MMI had a higher specificity (0.95) and sen sitivity (0.59) with respect to TRAb values (0.86 and 0.53, respective ly) for the prediction of the relapse of hyperthyroidism at the 24th m onth. CONCLUSIONS Basal thyroid hypoechogenicity cannot be used as an index of relapse of GD. MMI treatment induces evident changes in thyro id hypoechogenicity, mainly in patients who subsequently go into remis sion. The absence or a low grade of thyroid hypoechogenicity after MMI treatment seems to be a favourable prognostic index of remission of h yperthyroidism in GD.