Endocrine Abstracts

Introduction: Radioiodine (RAI) therapy is an inexpensive and reliable therapeutic option for Graves’ disease (GD). However, individual characteristics of the disease can influence therapeutic success. The identification of these factors may help to predict outcome and select optimal pre-treatment conditions.

Aim: To assess clinical, laboratory and radioactive parameters that may lead to RAI treatment failure in patients with GD.

Material and Methods: Retrospective study of 251 consecutive patients with GD treated with RAI therapy between January/2003 and February/2011. From those, 43 patients relapsed and needed additional RAI therapy-cases. Another 43 patients with therapeutic success (defined as euthyroidism/hypothyroidism 36 months after a single course of radioiodine therapy) were randomly selected-controls. The following parameters were analysed: age, gender, previous therapy with anti-thyroid drugs, thyroid function tests, thyroid mass, 24 h radioiodine uptake(24 h-RIU), administered therapeutic activity and time until relapse, using SPSS 21.0^®.

Results: Cohort of 251 patients, 202 female and 49 male, mean age 47±15.3 years. Relapse occurred in 43 patients (17.1%) 15.2±11.3 months after therapy. The case-control analysis showed a significantly higher initial FT4 (4.4±1 ng/dl vs 2.8±1.2 ng/dl;P>0.001) and TRAb (79±78.5 U/l vs 13.4±10.5 U/l; P<0.001) in the group with relapse. Regarding previous therapy with anti-thyroid drugs, the relapse group was more frequently treated with propylthiouracil compared with the control group (62.8% (n=27) vs 12% (n=10); P<0.001). The odds ratio of relapse in the patients treated with propylthiouracil compared with patients treated with methimazole was 6.171 (P<0.001). Patients with relapse had significantly higher mean thyroid mass (77.1±35.5 g vs 42.9±20.8 g; P<0.001) and 24 h-RIU (59.7±11.1% vs 55.5±14.1%; P=0.048). There were no differences concerning administered therapeutic activity between groups (1414.4±170.2 MBq vs 362.6±114.7 MBq; P=0.952). The thyroid mass was positively and significantly correlated with TRAb level (r=0.406;P=0.04).

Conclusions: In our cohort, the relapse of GD after radioiodine therapy was low (17.1%) and significantly associated with higher FT4 and TRAb levels, heavy thyroid glands and high values of 24 h-radioiodine uptake. Previous treatment with propylthiouracil was related with lower treatment success.