A serum predictor of Graves' disease recurrence following radioactive iodine therapy

Objectives Radioiodine (RAI) therapy with I-131 is the most common definitive treatment for Graves' disease. Although success rates are high, it remains unclear why a subset of patients revert to a hyperthyroid state, sometimes years following therapy. Previous research has identified a number of factors associated with RAI therapy failure, including RAI uptake, gender, age, and thyroid size. In this study we seek a serum marker that will predict the recurrence of Graves' disease following RAI therapy.

Methods All patients who underwent RAI therapy for Graves' disease from 2005 to 2011 at our institution were examined. Pre-therapy RAI uptake data, ultrasound results, RAI therapy dose, and demographic data were collected. Additionally, multiple serum markers were collected, including TSH, T4, T3, PTH, and calcium. Recurrence of Graves' disease was defined as a TSH <0.01 microIU/mL following therapy, repeat therapy, or both. 140 patients were examined, including 104 patients who remained hypothyroid or euthyroid for one year or longer and 36 patients who experienced a recurrence of hyperthyroidism. Statistical analysis was used to identify serum markers associated with the recurrence of Graves' disease.

Results No significant difference in pre-therapy RAI uptake, ultrasound results, or demographic data was found between patients who remained euthyroid or hypothyroid and those who experienced a recurrence of Graves' disease. A significantly greater number of patients who experienced a recurrence of Graves' disease had abnormally elevated T4 within two months following treatment (52.8% vs 27.6%, p=0.0081) and a greater than 1.0 microIU/mL increase in serum T4 from pre-therapy levels within two months post-therapy (36.1% vs 6.7%, p<0.0001).

Conclusions Post-therapy serum T4 levels are good predictors of hyperthyroidism recurrence. We recommend close monitoring for Graves' disease recurrence in patients with increases in serum T4 of greater than 1.0 microIU/mL from pre-therapy levels within two months post-therapy.