From the Research
Levothyroxine (Euthyrox) should be stopped before total body scintigraphy for thyroid cancer, with a recommended withdrawal period of 4-6 weeks prior to the procedure. This is based on the evidence from the study 1, which suggests that L-T4 withdrawal alone for 2-3 weeks is simpler and sufficient to allow TSH to reach a level of more than 30 mUI/l in the majority of patients without increasing morbidity from hypothyroidism.
The rationale behind stopping levothyroxine is to allow TSH levels to rise, which is necessary for stimulating any remaining thyroid tissue to maximize radioiodine uptake during the scan. Without proper withdrawal, residual or recurrent thyroid cancer tissue may not take up enough radioiodine to be detected on the scan, potentially leading to false-negative results.
Some key points to consider:
- The withdrawal period may vary depending on the individual patient's condition and the specific procedure being performed.
- An alternative approach is to continue levothyroxine and administer recombinant human TSH (rhTSH, Thyrogen) injections before the scan, which may be preferable for patients who cannot tolerate thyroid hormone withdrawal due to severe hypothyroid symptoms or medical comorbidities.
- The study 1 found that preparation for WBS with L-T3 does not prevent profound hypothyroidism and delays TSH elevation required for WBS, suggesting that L-T4 withdrawal alone may be sufficient.
- Other studies, such as 2, 3, 4, and 5, provide additional context and guidance on the management of thyroid cancer and the use of levothyroxine, but the most relevant and recent evidence for this specific question is found in 1.