Short course of oral lithium therapy as an adjunct in patients with thyrotoxicosis who failed initial radioiodine therapy: should this be worthwhile to consider in the absence of contraindications?

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Radioiodine therapy (RAI) has been utilized to treat hyperthyroidism successfully for more than seven decades and is currently considered the cornerstone of managing this condition along with antithyroid drugs (ATDs). The standard typical mean dose administered is a fixed dose of 10–15 mCi (370–555 MBq). Repeated doses are needed in cases of initial therapy failure; the success rates in individuals (with no pretreatment with ATDs) are estimated to be around 74% with 10 mCi (370 MBq) and 81% with 15 mCi (555 MBq) 1,2. Although retreatment is traditionally suggested after 6 months following RAI therapy, in individuals with minimal response additional RAI may be considered at 3 months after therapy. In day-to-day practice, however, one encounters a fraction of patients in whom hyperthyroidism persists even after two therapies and who need consideration for further retreatments.
Lithium enhances RAI retention in the thyroid, and hence adjuvant lithium with RAI has been proposed to be a practical approach to reducing the activity of RAI. Although the effect of lithium on radioiodine retention is well known, on practical grounds this approach is utilized only infrequently and there is no clear-cut consensus on which cases it would be rational to employ. Also, there is a dearth of knowledge among practitioners on the appropriate dose and regimen that would be logical for this purpose.
In recent years, there have been a total of four published studies (Table 1) in this domain, one of which has been included in this journal, and there have been some conflicting reports observed. Three studies 3–5 reported a favorable finding, whereas one study reported an insignificant advantage with lithium intervention 6. Interestingly, an obvious difference in regimen between the studies with different results was that the former three studies advocated the first dose of lithium 3–6 days before the administration of radioiodine administration 3–5 and the latter 6 advocated the first lithium dose on the day of radioiodine administration. Most of the studies advocated a dose of 900 mg lithium/day in three divided doses orally 3–6, which was found to be safe and well tolerated in almost all of the patients (the mean serum lithium concentration was 0.6 mEq/l in our study, with only one patient at a level of 1.5 mEq/l, without any obvious side effects).
Furthermore, in our study 5, we observed an added advantage of lithium priming that resulted in a significantly reduced serum-free T4 level, which was particularly evident in patients with diffuse toxic goiter. This would be an advantage in the clinical management of patients with uncontrolled disease when ATDs need to be discontinued and in the background of the fact that RAI can induce a transient increase in thyroid hormone levels. Thus, in summary, oral lithium in the aforementioned prescribed dosage would be a feasible and worthwhile option that could be considered in selected patients with hyperthyroidism who failed initial radioiodine therapy and the priming needs to be initiated 3–5 days before the scheduled administration of radioiodine for optimal results. Further prospective data in these groups of patients would help in defining the appropriate dosages and the regimen.
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