Endocrine Abstracts

Introduction: Radioiodine (Iodine-131) is a widely used treatment for thyrotoxicosis. Fluctuation in thyroid hormone levels following radioiodine treatment is common. Hypothyroidism occurs in approximately 5.5% of patients per month in the first 6 months, with onset time hard to predict. In contrast, some patients remain hyperthyroid either due to persistent pre-radioiodine thyrotoxicosis or transient exacerbation following radioiodine. We examined whether the block & replacement treatment (B&R; thionomides plus thyroxine) following radioiodine helped prevent fluctuation of thyroid hormone levels immediately post-radioiodine.

Methods: A retrospective case-note audit of 71 patients, undergoing radioiodine treatment for thyrotoxicosis in a 2-year period (2002–3). 25(35%) patients started B&R (carbimazole 40 mg and thyroxine 100 mcg daily) 7 days after radioiodine for 6 months (B&R group). 46(65%) patients were treated with thyroxine or thionomide, depending on thyroid function levels (non-B&R group). Thyroid function tests at 6 weeks post-radioiodine were compared in these groups.

Results: Of 71 patients, 61(86%) were women. 24(34%) had a diagnosis of Graves’ disease (positive thyroid antibodies, diffuse thyroid uptake or the presence of ophthalmopathy), 11(15%) had toxic multinodular goitre (patchy thyroid uptake), and in 36(51%) the diagnosis of thyrotoxicosis was undetermined. 5(7%) previously had thyroid surgery. 6(8%) previously had radioiodine. Before radioiodine, 45(63%) were on thionomides; 17(24%) on B&R; 28(40%) on thionomide alone. Medication stopped 7 days prior to treatment for both groups. Post radioiodine, 25 patients were treated with B&R and of the 46 patients in the non-B&R group, 12 were subsequently treated with thionomides. At 6 weeks, thyroid function tests in the B&R group showed that 12(48%) had biochemical euthyroidism, 10(40%) hyperthyroidism and 3(12%) hypothyroidism, as compared to 31(67%) euthyroidism, 10(21%) hyperthyroidism and 5(11%) hypothyroidism in the non-B&R group (P=ns).

Conclusions: Block & replacement treatment following radioiodine does not help to prevent fluctuation of thyroid hormone levels immediately post-radioiodine.