Endocrine Abstracts

Aim: Estimation of the effectiveness of a single low dose 0.05 mg rhTSH in increasing radioiodine uptake (RAIU) before ¹³¹I therapy for multinodular toxic goiter with low initial RAIU.

Patients: 24 patients (21 women, 3 men) with multinodular toxic goiter without prior antithyroid drug therapy. The initial 24 h RAIU was 21.1±8.44%; range, 6–39% and thyroid volume 64.14±22.49 ml; range, 24.8–109 ml.

Methods: A single dose of 0.05 mg rhTSH (Thyrogen, Genzyme) was given im. 24 h later diagnostic activity of ¹³¹I was administered and RAIU after 6, 24, 48 and 72 h was estimated. On the 4th day therapeutic dose of ¹³¹I adjusted to the increased RAIU was given. Therapeutic dose was calculated to deliver 120–150 μCi 131 I /ml thyroid tissue retained at 24 h.

Results: The significant 3.2-fold increase in 24 h RAIU to 66.9±13.05% after 0.05 mg rhTSH was noted. It allowed to reduce ¹³¹I therapeutic dose from the mean 46.6 mCi to 14.3 mCi. Shortly after rhTSH administration (24, 48 h) serum fT3 elevated from 3.08±0.8 pg/ml to peak value 6.02±1.36 pg/ml (P<0.001) and serum fT4 augmented from 19.16±3.59 pmol/l to peak value 29.04±10.11 pmol/l (P<0.001). Clinical signs of thyrotoxicosis exacerbation were mild to moderate. There was 1 case of painful thyroid enlargement without respiratory tract obstruction 24 h after rhTSH administration. Twelve months after ¹³¹I therapy 75% of patients were euthyroid, 6.5% hypothyroid and 18.5% still thyrotoxic. There was 45% reduction of thyroid volume.

Conclusions: Administration of a single dose of 0.05 mg rhTSH enhances 3.2-fold RAIU in patients with multinodular toxic goiter. This method enables significant ¹³¹I dose reduction but should be carefully undertaken because of the risk of thyrotoxicosis exacerbation and thyroid volume enlargement.