Endocrine Abstracts

Background: Radioiodine is an effective treatment for Graves’ hyperthyroidism. In most cases this therapy renders the patient completely hypothyroid. As a consequence they will require lifelong thyroid replacement therapy. Now it is controversial whether radioiodine should be given in a sufficient dose to induce hypothyroidism or a lower dose in an attempt to achieve a euthyroid state.

Case Report: A 71-year-old woman with a 30 years history of Graves’ disease and frequent recurrences of thyrotoxicosis presented with tremulousness, palpitations, dyspnea, progressive fatigue and weight loss. Examination revealed BMI 28 kg/m², Ps 105 bpm, BP 150/80 mmHg. An ECG showed sinus tachycardia. Laboratory analyses showed recurrence of hyperthyroidism: TSH 0,19 mUI/l (N 0,27-4,2), FT4 1,86 ng/dl (N 0,93-1.52), positive TSH receptor antibodies (5,62 IU/l). The thyroid ultrasonography showed diffusely enlarged thyroid (total volume 54 ml). Thyroid scintigraphy showed increased 24-hour radioiodine uptake (90%) with diffuse activity on the scan image. She was treated with methimazole (30 mg/day) and anaprilin (40 mg/daily) and the patient’s condition improved. According to medical history she had poor control of the disease by drugs. Surgery was risky for the elderly patient. Therefore radioactive iodine ablation was suggested. Iodine-131 was administered orally at individual dosage of 13 millicuries (based on 200 microCi/g of thyroid tissue). Previous to therapy thyroid laboratory results showed TSH 1,75 mUI/l, FT4 0,68 ng/dl. Methimazole was canceled 3 days before the procedure. The introduction of I-131 was well tolerated. Patient had normalization of thyroid function tests within 4 weeks. Hypothyroidism occured 12 weeks after radioiodine (TSH 46,4 mUI/l, FT4 0,23 ng/dl). Then thyroid replacement therapy (75 mg of levothyroxine) was initiated. However, within the 6 month after treatment the patient presented subclinical hyperthyroidism and the dose of levothyroxine was reduced and then canceled. Ultrasound showed residual thyroid tissue (total volume 18 ml). The patient is currently euthyroid (TSH 0,58 mUI/l) and under follow-up.

Conclusion: For patients with Graves’ disease, a high dose of radioiodine is directly related to the cure rate and the incidence of hypothyroidism. The most preferred is to individualize the radioiodine dose based upon the size of the thyroid gland and the 24-hour radioiodine uptake. In this case, a persistent goiter suggests incomplete destruction of the gland and the possibility of persistent autonomous thyroid tissue. After radioiodine, all patients require monitoring for hypothyroidism or persistent hyperthyroidism.