From the Research
Methimazole should be discontinued for at least 72 hours before a radioactive iodine scan, as this timeframe allows for optimal iodine uptake and accurate scan results. This recommendation is based on the study by 1, which found that discontinuing methimazole for 24-48 hours, 48.1-72 hours, or 72.1-168 hours before radioiodine therapy did not significantly affect the response to treatment. However, to prioritize morbidity, mortality, and quality of life, it is essential to ensure that the thyroid gland has regained its ability to take up iodine, allowing for proper visualization during the scan.
When considering the discontinuation of methimazole, it is crucial to weigh the potential risks and benefits. Temporarily stopping methimazole may cause hyperthyroid symptoms to return or worsen during this period. However, this risk can be mitigated by closely monitoring the patient's symptoms and adjusting the discontinuation period accordingly.
The following key points should be considered when discontinuing methimazole before a radioactive iodine scan:
- The thyroid gland's ability to incorporate iodine is blocked by methimazole, potentially leading to false-negative results if not stopped beforehand.
- Discontinuing methimazole allows the thyroid gland to regain its ability to take up iodine, enabling proper visualization during the scan.
- Patients should be aware of the potential for hyperthyroid symptoms to return or worsen during the discontinuation period.
- The exact timing of discontinuation should be confirmed with the nuclear medicine department performing the scan, as protocols may vary slightly between facilities.
In terms of the evidence, the study by 1 provides the most recent and highest-quality data on the topic, making it the primary basis for this recommendation. While other studies, such as 2 and 3, provide additional context and insights, they do not supersede the findings of 1 in terms of recency and quality. Therefore, the recommendation to discontinue methimazole for at least 72 hours before a radioactive iodine scan is based on the best available evidence, prioritizing morbidity, mortality, and quality of life.