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There is still no consensus on the best treatment for Graves’
disease. In the USA 131I is the preferred therapy in adults, while ATD are favored in
Europe and Japan (8), although less than 50% will achieve long-term remission by this
therapy. 131I is thought to be the most cost-effective therapy. Advantages and
disadvantages are given in table 3. Generally, oral 131I doses of 100 µCi (3.7 MBq) per gram thyroid tissue corrected for a 100% 24 h 131I uptake have been given (9). This will approximately render 70% of patients euthyroid within 3 months, given that antithyroid drugs are not resumed. Roughly 70% are cured with one dose and 90% with two doses. It is generally believed that pretreatment as well as post treatment with ATD decreases the effect of 131I4. Prospective randomized studies on how many days ATD have to be withdrawn, if at all, and whether there is a difference between carbimazole, methimazole and propylthiouracil are lacking. Table 2: Contraindications for radioiodine treatment in benign thyroid disease Absolute contraindications
The risk of hypothyroidism depends on the 131I dose. The lower the dose, the lower the incidence of hypothyroidism within the first year of therapy and the higher the frequency of persistent hyperthyroidism. Using the above dose-algorithm some 20% of patients will become hypothyroid within the first year, while myxedema incidence beyond the first year seems at large uninfluenced by 131I dose at 2–3% per year (9,10). The risk of hypothyroidism is roughly 50% after 10 years and if given at a young age inevitably causes hypothyroidism (5,9,10). Based on the existing information, it could be speculated whether a meticulously calculated 131I dose is cost-effective and worth while (10,11). Thyroid size reduction has received little attention. Thyroid volume – determined ultrasonically – can be reduced by approximately 50–60% within one year (9), with little subsequent reduction. Roughly, half of this decrease is seen within 3 months of therapy (9). There is no significant acute increase in thyroid volume or obstructive symptoms, after 131I administration12. Normalization of thyroid volume – irrespective of initial thyroid size (9) – is the rule, and secondary increase in thyroid volume should not be anticipated, except in the patient affected by radiation thyroiditis, which is rare. The initial 131I dose reduces thyroid volume in all patients, also in patients needing subsequent 131I doses due to persistent hyperthyroidism. The dose can be repeated and additional thyroid volume reduction expected. Thyroid volume reduction is generally higher in patients becoming hypothyroid than in those remaining eu- or hyperthyroid (9). Radiation thyroiditis is seen in few percent within the first months of 131I-therapy and easily treated with salicylates or corticosteroids. Recent evidence unequivocally demonstrates that 131I-treatment in Graves’ disease carries a risk of development or worsening of ophthalmopathy in 15% of patients (5% needing treatment) (13). This worsening is often transient and can be prevented by the administration of prednisolone (13). While this study may indicate that the combination of 131I and prednisolone should have a more prominent place in the therapy of Graves’ hyperthyroidism with eye-symptoms, only 6% of European Thyroid Association (ETA) members would prefer this treatment14. Active ophthalmopathy is thus regarded by most ETA members as a relative contraindication for 131I-therapy. The overwhelming majority of young patients with hyperthyroidism have Graves’ disease (15). Since remission rates on ATD are lower in young subjects than in adults, 131I-therapy has been used also in children (15). Although used down to the age of 5 by some, and the rarity of thyroid malignancy in 131I-treated children (4 reported cases) (15), we are reluctant to administer this therapy for subjects below 20 years of age. However, as data on side-effects accumulates we, as have others, have treated younger and younger subjects. There is at present no consensus as to a lowest age limit. |
