Hyperthyroidism radioiodine

To ensure a definitive cure of hyperthyroidism, radioiodine treatment or surgery is available. Long-term use of thionamide drugs may be advisable only in severely ill and multimorbid patients, who are unable to undergo one of these two treatments. 

The selective uptake of iodide ion by the thyroid gland is the basis of radioiodine treatment in hyperthyroidism, mainly with although various other radioactive isotopes ate also used (40,41). With a half-life of eight days, the decay of this isotope produces high energy P-particles which cause selective destmction within a 2 mm sphere of their origin. The y-rays also emitted are not absorbed by the thyroid tissue and are employed for external scanning. 

Toxic adenomas may result in hyperthyroidism with larger nodules. Because there may be isolated elevation of serum T3 with autonomously functioning nodules, a T3 level must be measured to rule out T3 toxicosis if the T4 level is normal. After a radioiodine scan demonstrates that the toxic thyroid adenoma collects more radioiodine than the surrounding tissue, independent function is documented by failure of the autonomous nodule to decrease its iodine uptake during exogenous T3 administration. 

In most patients with hyperthyroidism, T3, T4, FT4, and FT3 are elevated and TSH is suppressed (Table 38-2). Radioiodine uptake is usually markedly elevated as well. Antithyroglobulin, thyroid peroxidase, and TSH-R Ab [stim] antibodies are usually present. 

Bartalena L, Marcocci C, Bogazzi F, Panicucci M, Lepri A, Pinchera A. Use of corticosteroids to prevent progression of Graves ophthalmopathy after radioiodine therapy for hyperthyroidism. N Engl J Med 1989 321(20) 1349-52. 

In 50 women taking levothyroxine either for primary thyroid failure or for hypothyroidism secondary to radioiodine treatment for hyperthyroidism, there was no difference between the two groups in terms of bone density at the hip or spine and no difference from the reference population (31). In addition, there was no correlation between bone density and circulating thyroid hormone concentrations or duration of levothyroxine replacement. These findings are reassuring, although large studies of fracture risk are required, in view of previous evidence of an adverse effect of levothyroxine on bone mineral density, especially in post-menopausal women (32). 

Lithium blocks the release of iodine and thyroid hormones from the thyroid and has been used to treat hyperthyroidism, as an adjunct to radioiodine therapy (602-605) and in metastatic thyroid carcinoma (606). However, it can also cause hyperthyroidism. Lithium enhanced the efficacy of radioiodine in 23 patients (607), but was ineffective in a larger comparison of lithium (n = 175) or radioiodine alone (n = 175) (608). In 24 patients with Graves disease, lithium attenuated or prevented increases in thyroid hormone concentration after methimazole withdrawal and radioiodine treatment (602,609). 

Bogazzi F, Bartalena L, Brogioni S, Scarcello G, Burelli A, Campomori A, Manetti L, Rossi G, Pinchera A, Martino E. Comparison of radioiodine with radioiodine plus lithium in the treatment of Graves hyperthyroidism. J Clin Endocrinol Metab 1999 84(2) 499-503. 

Bal CS, Kumar A, Pandey RM. A randomized controlled trial to evaluate the adjuvant effect of lithium on radioiodine treatment of hyperthyroidism. Thyroid 2002 12(5) 399-405. 

Lithium blocks the release of iodine and thyroid hormones from the thyroid and has been used to treat hyperthyroidism, as an adjunct to radioiodine therapy... 

Antithyroid drugs and hyperthyroidism thionamides, drugs that block sympathetic autonomic activity, iodide and radioiodine... 

In hyperthyroidism the beneficial effects of a single dose may be felt in one month, and patients should be reviewed at 6 weeks to monitor for onset of hypothyroidism. The maximal effect of radioiodine may take 3 months. P-adrenoceptor blockade and, in severe cases, an antithyroid drug (but see footnote 1) will be needed to render the patient comfortable whilst waiting this is more likely when radioiodine is used for treatment of patients with relapsing thyrotoxicosis. Very rarely radiation thyroiditis causes excessive release of hormone and thyroid storm. Repeated doses are sometimes needed. 

Larger doses of radioiodine are used for thyroid carcinoma than for hyperthyroidism, and there is an increased incidence of late leukaemia in these patients. The treatment of thyroid carcinoma is highly specialised. 

Radioiodine uptake can be used to test thyroid function, though technetium would be more usual. Scanning may be used for the identification of solitary nodules, and in the differential diagnosis of Graves disease from the less common thyroiditides (e.g. de Quervain s thyroiditis). In the latter, excessive thyroid hormone release caused by follicular cell damage can cause clinical and biochemical features of hyperthyroidism, but uptake is reduced. 

In 10 552 Swedish patients (mean age 57 years) who received I for hyperthyroidism (mean follow-up 15 years) there were increases in overall cancer mortality and deaths due to carcinoma of the stomach, lung, and kidney. While the findings for stomach cancer may be of significance, for tumors at other sites, because of an association with time after I treatment (58 cases at 10 years or more of follow-up against the expected 44 cases), the lack of a relation between cancer mortality and either the time from radioiodine treatment or the dose administered argues against a carcinogenic effect of radioiodine (SEDA-17, 475) (25). 

Ross DS, Nussbaum SR. Reciprocal changes in parathyroid hormone and thyroid function after radioiodine treatment of hyperthyroidism. J Clin Endocrinol Metab 1989 68 1216-9. 

FranWyn JA, Maisonneuve P, Sheppard M, et al. Cancer incidence and mortality after radioiodine treatment for hyperthyroidism A population-based cohort study. Lancet 1999 353 2111-2115. 

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