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The fact that remission of hyperthyroidism on ATD cannot be
expected, in addition to the relatively high risk of surgical complications, even in
eligible patients (16), has lead a number of centers (including ours) to offer radioiodine
as the first choice of therapy in the majority of patients. 131I is considered safe and
appropriate in nearly all types of hyperthyroidism, especially in elderly patients, as is
most often the case with multinodular toxic goitre (17). Compared to that in Graves’
disease, surprisingly little data is available regarding effects and side-effects of
131I-therapy in multinodular toxic goitre (Table 3).
Most often oral 131I doses of 100–150 µCi (3.7–5.55 MBq) per gram thyroid tissue corrected for 100% 24 h 131I uptake, is recommended. Again, many do not use meticulously calculated dose-algorithms but prefer fixed maximum outpatient doses. There is at present no evidence of one regime being better than the other10. Only 50% of patients become euthyroid within 3 months of 131I-therapy, given that ATD are not administered (16,18). Twenty to forty percent need additional 131I-therapy and even up to 5 treatment sessions will not cure all patients (18). As with Graves’ disease, the role of pre- and post radioiodine treatment with ATD on the effect of 131I is not known. Thyroid volume can be halved within 1–2 years of 131I-therapy with approximately two thirds of this reduction becoming evident within 3 months of therapy (18). Even 131I doses that do not cure the patients will reduce thyroid volume by 25% on average (18). The reduction is independent of pretreatment with antithyroid drugs (18) and no additional reduction beyond two years can be expected. There is no clinically significant acute increase in thyroid volume or obstructive symptoms after 131I treatment (12,19). In fact, a relief of compressive symptoms, a decrease in upper airway obstruction – as estimated by pulmonary functioning testing and flow-volume loops – and an increasing cross-sectional area of the tracheal lumen, can be expected in most patients (19,20). Also patients with monstrous (150 ml) and partly intrathoracic goitres have been treated with beneficial results (19,20). In these patients very large doses of 131I are needed. Treatment is given on an in-patient basis and 131I dose calculated using 96 h 131I uptake measurement and thyroid volume determination by MR-scan (19). Isolation for 1–2 weeks is often necessary (but may depend on local regulations) making this a cumbersome alternative in the few patients not found suited for thyroidectomy (19,20). In these monstrous goitres a 30–40% volume reduction within one year can be expected (19,20). The treatment can be repeated with an expected additional volume reduction (18,21). Normalization of thyroid volume is rare, as is secondary increase in thyroid size. Radiation thyroiditis is an infrequent complication18. Graves’ like hyperthyroidism has been demonstrated in 5 of 100 patients (5%) with multinodular toxic goitre (22) or similar to that described in non-toxic multinodular goitre (23). It is related to appearance of TSH-receptor(TSHR)-ab and typically occurs 3–6 months after 131I-therapy. The risk of hypothyroidism is lower than in Graves’ disease since only part of the gland takes up 131I. In the only long-term (median 6 years) follow-up of a large population (130 subjects) the risk of hypothyroidism was found to be 14% after 5 years (18) or similar to that found in non-toxic multinodular goitre (21). Pretreatment presence of anti-TPOab seems to confer an increased risk of developing both Graves’ like hyperthyroidism (10%) and hypothyroidism (30%) as compared to 0.8% and 5%, respectively, in anti-TPOab negative subjects (22). Table 3: Effects and side-effects of 131I-therapy for toxic goitre Advantages
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