Radioiodine treatment

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. 

Graham GD, Burman KD. Radioiodine treatment of Graves disease. An assessment of its potential risks. Ann Intern Med 1986 105(6) 900-5. 

Goh KO. Radioiodine treatment during pregnancy chromosomal aberrations and cretinism associated with maternal iodine-131 treatment. J Am Med Womens Assoc 1981 36(8) 262-5. 

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). 

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. 

Quick relief can be obtained with a p-adrenoceptor blocking drug (judge dose by heart rate) though these do not block all the metabolic effects of the hormone, e.g. on the myocardium, and the basal metabolic rate is unchanged. For this reason they should not be used as sole therapy except in mild thyrotoxicosis in preparation for radioiodine treatment, and should be continued in these patients until the radioiodine has taken effect. They do not alter the course of the disease, nor biochemical tests of thyroid function. Any effect on thyroid hormonal action on peripheral tissues is clinically unimportant. It is desirable to choose a drug that is nonselective for pj and p2 receptors and lacks partial agonist effect (e.g. propranolol 20-80 mg 6-8-hourly, or timolol 5 mg once daily). Usual contraindications to P-blockade (see p. 478) should be observed, especially asthma. 

In the first year after treatment 20% of patients will become hypothyroid. After this 5% of patients become hypothyroid annually, perhaps because the capacity of thyroid cells to divide is permanently abolished so that cell renewal ceases. Patients must therefore be foUowed up indefinitely after radioiodine treatment, for most are likely to need treatment for hypothyroidism eventually. Because such followup over years may fail and because the onset of hypothyroidism may be insidious and not easily recongnised, some physicians prefer deliberately to render patients hypothyroid with the first dose and to educate them on the use of replacement therapy which is safe and effective. 

Medical experience had eliminated the fear that radioiodine causes carcinoma of the thyroid, and led to its use in patients of all ages. However the Chernobyl disaster revived concern about exposure of children and it would be wise again to restrict radioiodine treatment to adults. Pregnant women should not be treated with radioiodine because it crosses the placenta. 

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. 

Tallstedt L, Lundell G. Radioiodine treatment, ablation, and ophthalmopathy A balanced perspective. Thyroid 1997 7 241-245. 

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. 

Other possibilities for identification (ID) of patients with thyroid disorders are searching in different records or databases, such as records of diagnoses of discharge from hospitals, prescriptions of thyroid medicaments (antithyroid drugs and levothyroxine), and records of treatments for thyroid disorders including thyroid surgery and radioiodine treatments. Finally, diagnosis of overt thyroid dysfunction is based on a biochemical thyroid function test, and laboratory databases with results of analyses of thyrotrophin (TSH) and thyroid hormones in a population cohort, and records of serum TSH in newborns may be used to identify new patients (Kempers et al., 2006). 

If NIS expression can be increased in cancer cells, i.e., by gene transfer or chemical induction, this could make radioiodine treatment possible not only in thyroid disease, but also in gastric cancer. 

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. 

Table 81.3 Choice between radioiodine treatment and surgery...

As for the efficiency of radioiodine treatment, elimination of hyperthyroidism has been reported to be achieved in approximately 90% of the patients with toxic adenoma and 60-80% of patients with toxic multinodular goiter (Dietlein et ai, 2004 Ferrari et al., 1996 Hegedus et ai, 2003 Le Moli et al, 1999 Nygaard et al., 1999 Reiners and Schneider, 2002). 

Other nonsurgical, but still invasive, treatment modalities have been employed to destroy toxic adenomas such as ethanol injection guided by ultrasound. Even though ethanol injection may present a helpful approach in selected patients, cure rates are inferior to those of radioiodine treatment and complication rates have been reported to be close to those of conventional surgery. 

The choice of treatment is discussed by the specialist and the patient. In the absence of one of the indications for surgery, we would suggest radioiodine treatment as the first choice. In case of overt hyperthyroidism, pretreatment with antithyroid drugs may be necessary. Optimum treatment modalities including the presence of a suppressed TSH in toxic adenoma or multinodular goiter should be established. On the one hand, patient s fears regarding radiation exposure and, on the other hand, possible surgical complication often infiuence the decision and have to be addressed. 

In case malignancy has not been known prior to the operation and is incidentally discovered by histological workup, the patient will be reoperated within 4-7 days to complete total thyroidectomy. One exception applies in younger adults with papillary thyroid cancer measuring less than 1 cm, who show no indications of nodular or metastatic spread of the disease, where, because of the excellent prognosis, there may be no need for total thyroidectomy and subsequent radioiodine treatment. 

Radioiodine treatment is particularly well-suited for toxic adenoma and multinodular toxic goiter. Surgery is... 

There have only been a limited number of studies that have addressed the value of a low-iodine diet prior to radioiodine administration, summarized in Table 99.2. It is difficult to define the optimal extent of reduction in iodine intake and consequently urinary excretion when a low-iodine diet is used in preparation for radioiodine administration. Park and Hennessey (2004) classified a reduction in urinary iodine/creatinine ratios to <50p,g/g as excellent, and to 51—100p,g/g as adequate preparation prior to radioiodine treatment. Comparison between studies is further compfic-ated by the different measures used to measure urinary iodine, including 24 h urinary iodine, iodine/creatinine ratios and spot urine iodine measurements. Spot urinary iodine concentrations which are not normalized to urine creatinine are... 

Morris et al. (2001) retrospectively reviewed the ablation rates following initial radioiodine treatment postthyroidectomy for differentiated thyroid cancer patients in a single institution in the US. In this center a written comprehensive low-iodine diet was introduced in 1996 to replace a policy of limited simple verbal advice to avoid iodized foods, enabling a retrospective comparison between two different cohorts. Successful ablation was deemed to have occurred if there was no radioiodine uptake in the area of the thyroid bed on a diagnostic uptake scan performed between 4 and 42 months post-ablation. The was no statistically significant difference in ablation rates between 50 patients treated prior to 1996 who received minimal dietary advice with a 62% successful ablation rate, and with 44 patients post-1996 who received the... 

Radioiodine treatment may destroy occult microcarcinoma and reduces the rate of progression of metastatic tumor (Hershman et ai, 1995 Schlumberger, 1998). It is apparent that the efficacy of radioiodine treatment depends on maximizing the uptake of radioiodine and prolonging the period of time it persists in the thyroid tissue. 

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