Effects of Amiodarone Therapy on Thyroid Iodine Content as Measured by X-Ray Fluorescence

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Abstract
Thyroid iodine content (TIC) was measured by x-ray fluorescence in 68 patients who had received amiodarone treatment for varying intervals (1 g/week for 1–120 months). Thirty-six patients were euthyroid; the mean TIC of the patients (n = 15), who had been treated for less than 12 months was 30 ± 19 (±sd) mg, twice the normal mean value (14.6 ± 5.0 mg), and it was 39 ± 17 mg in those (n = 16) who had been treated for 12–60 months and 29 ± 6 mg in those (n = 5) who had been treated longer (>60 months). Nineteen patients were hyperthyroid and had elevated TIC values. Of them, 6 patients had a goiter; their TIC (50 ± 19 mg) was not significantly different from that of the hyperthyroid patients with no goiter (55 ± 29 mg), but they became hyperthyroid more rapidly. Thirteen patients were hypothyroid; none had TIC values above the normal range, and it was below 2.5 mg in 5 patients. A sequential study was undertaken in 11 euthyroid patients who had no detectable antithyroid antibodies. TIC did not increase during treatment in 2 patients; both developed hypothyroidism, which was transient in 1 despite continuation of amiodarone treatment. The TIC initially increased during amio-darone treatment in the other 9 patients, leveling off at the end of the first year. The TIC rose well above the upper limit of the normal range in 4 patients, of whom 2 became hyperthyroid during the second year of treatment. TIC remained within the normal range in the other 5 patients, of whom 3 became hypothyroid after 12–24 months of treatment (1 subclinical, 2 overt). Although the TIC was significantly higher in the patients with hyperthyroidism than in the patients who remained euthy-roid, the TIC test cannot be used to predict the occurence of hyperthyroidism. The latter must be diagnosed on the basis of clinical symptoms and a frank elevation of serum thyroid hormone levels. Conversely, patients whose TIC values do not increase during treatment or remain within the normal range should be considered at risk for hypothyroidism.