Recovery time from hyperthyroidism after individualized radioiodine treatment in patients with uni or multifocal autonomy

Abstract

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Objectives: This study aimed to evaluate the recovery time from hyperthyroidism after individualized radioiodine therapy in patients with uni or multifocal autonomy.

Methods: One hundred and nine patients (age 67+/-10 years,78F,31M) with uni (44%) or multifocal (56%) autonomy were treated over the last 5 years. A subclinical hyperthyroidism was found in 52% of patients with suppressed TSH (normal range: 0.26-4.2 mU/L) and normal serum values of FT3 and FT4 (range: 3.8-8.0 pmol/l and 9.0-20.0 pmol/l respectively). Clinical hyperthyroidism was observed in the remaining 48% with suppressed TSH and high FT3 and/or FT4 serum values. After a 123I dosimetric study based on thyroid uptake measurements at five time points, each patient received an individualized 131I dose. Patients were free from antithyroid drugs over 1 month before dosimetry and therapy. Patient clinical status was monitored by repeated TSH, FT3 and FT4 serum value assays 1,3,6,12 months after therapy and then once a year. Mean administered activity was 364+/-129 MBq [range 111-625 MBq] and mean delivered dose was 145+/-45 Gy [range 59-311 Gy]. Mean follow up was 2.9+/-1.8 years with a maximum of 5 years and more than 71% of patients for each follow up time point was monitored.

Results: Clinical conditions following therapy at different follow up time points are reported in the table. Eighty-two percent of patients was cured within 6 months. Among the remaining patients with persistent hyperfunction of thyroid gland 53% became euthyroid within a year after the treatment. The latest resolutions of hyperthyroidism were observed up to 3 yrs.

Conclusions: Although the re-treatment of hyperthyroidism is mandatory after unsuccessful 131I therapy, a late normalization of thyroid function is not uncommon. Our data suggest that a second 131I dose should be administered at least one year after the first treatment.