X034

A challenging case of radioiodine-refractory Graves’ disease

R Ramli, R Troke, F Wernig, A DiMarco, F Palazzo, S Kahn, Z Win, N Hill, G Williams, K Meeran, E Hatfield, Imperial Healthcare NHS Trust

Our patient initally presented 8 years ago with supraventricular tachycardia (SVT) at the age of 14, for which she underwent cardiac ablation. Her arrhythmia recurred and blood tests revealed thyrotoxicosis with positive TSH receptor antibodies (11.1 U/mL [0 - 0.3]). Her aunt had a thyroid goitre removed, but there is no family history of autoimmune thyroid disease. She had no evidence of Graves’ opthalmopathy.

She was started on thionamide treatment in addition to Ivabradine and Propranolol. Her adherence to therapy was suboptimal and she remained thyrotoxic with frequent attendances to casualty due to SVT. She therefore received radioiodine treatment (745 MBq, November 2015), but unfortunately returned a month later with SVT and persistent thyrotoxicosis. She was restarted on anti-thyroid treatment and received a second radioiodine dose (755 MBq, April 2016). This was again unsuccessful, and, as she declined total thyroidectomy, a third dose of radioiodioine was administered (810 MBq, July 2016). A post-treatment 5-minute thyroid uptake Technetium scan showed good uptake within both lobes of the thyroid gland. She improved biochemically 10 weeks later (T4 8.4 pmol/L, TSH 0.01 mU/L), but unfortunately became thyrotoxic again soon after (T4 34.4 pmol/L, T3 >46.1 pmol/L, TSH <0.01 mU/L). A Technetium uptake scan showed diffuse increased homogenous distribution of tracer throughout both lobes of the thyroid gland with suppression of the normal background activity (uptake function 15.7%). Two further radioiodine treatments were given in February 2017 (780 MBq) and March 2017 (597 MBq) with Lithium administration 3 days prior to radioiodine. A day 1, 3 and 7 post-therapy whole body uptake technetium scan confirmed retention of radioiodine within the thyroid gland with no sites of extrathyroidal uptake. She unfortunately remained clinically and biochemically thyrotoxic and following further discussion, the patient finally agreed to have surgery. She received 10 days of high-dose potassium iodide which rendered her euthyroid and successfully underwent a total thyroidectomy in October 2017. She was commenced on Levothyroxine postoperatively, remains well and under close surveillance.

Radioiodine treatment is highly effective in the treatment of Graves’ disease with cure rates approaching 100%. Rapid thyroidal iodine turnover and/or large, isoechoic goitres have been associated with poor response to radioiodine treatment. Pre-treatment with lithium may prolong radioiodine retention and may increase the efficacy of radioiodine therapy and was therefore used in our patient, but remained unsuccessful. This is an extremely unusual case of radioiodine-resistant Graves’ disease whose disease remained active following a total of 5 doses of radioiodine.