Endocrine Abstracts

Background: Iodine-131 (I-131) has been used to treat hyperthyroidism for half a century. Recent recommendations from the RCP London and British Thyroid Association suggest 400 MBq in most cases, but 500–600 MBq for toxic multinodular goitre (MNG). We have reviewed our clinic data with particular reference to response to a standard dose, 400 MBq, given to treat hyperthyroidism.

Method: Casenotes of 88 patients who received 400 MBq I-131 for hyperthyroidism were reviewed.

Underlying diagnosis was based upon isotope and ultrasound scans, serum anti-thyroid antibody (TBII and TPo) titre and clinical features; patients’ thyroid status at time of treatment and at 12 months following treatment was recorded.

Results:

a. Patients

Graves’ n=19, MNG n=31, adenoma n=5, Unclassified n=33.

b. Outcome

At 12 months, 19 (21.6%) were euthyroid and 34 (38.6%) hypothyroid and 35 (39.7%) patients remained hyperthyroid and requiring anti-thyroid medication. Of the 35 patients who had not responded to I-131, 36.6% had MNG, 31.5% Graves’, 20% toxic adenoma and 16.6% unclassified patients

At 12 months 22.6% MNG, 47.4% Graves’, 40% adenoma and 48.5% unclassified patients had become hypothyroid.

No single factor was predictive of outcome, although none-significant trends were observed for the presence of anti-thyroid antibodies (hypothyroidism) and normal serum fT4 at baseline (euthyroidism). When hyperthyroid versus euthyroid plus hypothyroid outcomes were compared, no predictive factor for persistent hyperthyroidism was identified.

Comparing the responses in the MNG and Graves’ groups, the odds of having a normal outcome at 12 months in the MNG group were 9.9 times that of the Graves’ group (95% CI 1.16–84.5) as a consequence of increased rates of hypothyroidism in the Graves’ group.

Conclusion: The use of 400 MBq for all patients in our clinic would not appear adversely to affect the outcome for patients with MNG.