Endocrine Abstracts

Radioiodine (131-I)- in use for more than 50 years for hyperthyroidism, with or without goitre, and also more recently for non-toxic goitre- has proven effective in the treatment of hyperthyroidism as well as in reducing goitre size. In hyperthyroidism, one or two 131-I doses will cure nearly all patients. Factors such as: sex, age, morphological goitre type, size of goitre, presence of thyroid autoantibodies, and pre- and post-radioiodine antithyroid drug (ATD) therapy influence the outcome, which is difficult to predict. Therefore, many use fixed (185–800 MBq) instead of calculated (corrected for thyroid size and 131-I uptake) doses of 131-I. Thyroid size reduction of 30–70% can be achieved within one year of therapy. Side effects include insufficient effect, myxoedema, thyroiditis, flare-up in hyperthyroidism and ophthalmopathy, but not thyroid cancer. There is insufficient data comparing long-term ATD therapy, 131-I, and surgery.

In non-toxic goitre-where levothyroxine has little or no goitre reducing effect-surgery is declined by or contraindicated in many patients. In the UK many patients are offered watchful waiting, while 131-I therapy is increasingly used in a number of other European countries (especially in Denmark). 131-I reduces goitre size by 30–70% within 12 months of therapy, depending on factors such as: duration of goitre, thyroid size, thyroid morphology, presence of thyroid antibodies, and pre-treatment with recombinant human TSH (rhTSH). The latter increases thyroid size reduction by 30–50%, in preliminary studies, at the expense of an increase in transient side effects, especially hyperthyroid symptoms, thyroid swelling and pain, and risk of myxoedema. Without rhTSH prestimulation, side effects of 131-I are fewer but qualitatively the same as when used for treating hyperthyroidism.

In conclusion, 131-I is a qualified alternative to ATD or surgery in hyperthyroidism and surgery or watchful waiting in non-toxic goitre. In my view, it should be used more frequently. When investigated, there is little consensus on preferred therapy (in a standard case), most likely due to lack of studies comparing the options.