Endocrine Abstracts

Introduction: Radioiodine treatment (RAIT) is an effective definitive treatment for Graves’ Disease (GD) and Toxic Nodular Goiter (TNG). The aim of this study was to analyze demographic and clinical factors affecting the outcome of RAIT in patients with hyperthyroidism.

Methods: Retrospective review of patients treated with RAIT for hyperthyroidism. A fixed dose of 10 mCi was administered to patients with GD and 15 mCi to patients with TNG. Treatment success was defined as euthyroidism or hypothyroidism (subclinical/overt hypothyroidism) 12 months after RAIT.

Results: 217 patients were included; 122 with GD and 95 with TNG (52 patients with toxic multinodular goiter and 43 with Toxic Adenoma). RAIT was more effective in TNG than in GD (94.7% vs 71.3%, P<0.05). Gender, previous thyroid function and thyroid volume were significantly as-sociated with an effective outcome in patients with GD (P<0.05). No clinical or demographic factors affected the outcome in patients with TNG, although a higher Tc99 uptake on scintigraphy was associated with persistent hyperthyroidism. Hypothyroidism was more common in GD (62.3% vs 41.1%, P=0.001). Hypothyroidism was significantly more frequent in smaller nodules (26±8 mm vs 32±11 mm, P<0.05) and in lower thyroid volumes (24.3±14 ml vs 37.7±19 ml, P<0.05).

Conclusion: Thyroid volume seems to have a significant influence on the development of hypothyroidism after the treatment and, in patients with GD, the efficacy of RAIT. In GD, larger goiters may need a greater dose and beneficiate from a calculated dose of radioiodine instead of a fixed predefined dose. In TNG, a fixed dose of 15 mCi successfully cured hyperthyroidism in almost all patients although in selective patients with smaller thyroid nodules or smaller goiters a lesser RAIT dose may restore euthyroidism.