What is the role of radioiodine uptake in the workup of subacute thyroiditis?

Updated: Mar 23, 2021
  • Author: Stephanie L Lee, MD, PhD; Chief Editor: Romesh Khardori, MD, PhD, FACP  more...
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Answer

Neither radioiodine uptake nor thyroid scanning is indicated unless pain is mild or absent, in which case Graves disease might be considered in the differential diagnosis.

In subacute thyroiditis, radioiodine uptake is low (< 1-2% at 24 h), reflecting thyrotoxicosis due to a discharge of preformed stores of thyroid hormone and resulting from an increase in synthesis (see the image below). Administration of TSH usually fails to produce normal increase in uptake, probably because thyroid cell damage reduces the ability of the cell to respond to TSH.

Absence of iodine-123 (123I) radioactive iodine up Absence of iodine-123 (123I) radioactive iodine uptake in a patient with thyrotoxicosis and lymphocytic (subacute painless) thyroiditis. Laboratory studies at the time of the scan demonstrated the following: thyroid-stimulating hormone (TSH), less than 0.06 mIU/mL; total thyroxine (T4), 21.2 mcg/dL (reference range, 4.5-11); total triiodothyronine (T3), 213 ng/dL (reference range, 90-180); T3-to-T4 ratio, 10; and erythrocyte sedimentation rate (ESR), 10 mm/h. The absence of thyroid uptake, the low T3-to-T4 ratio, and the low ESR confirm the diagnosis of lymphocytic thyroiditis.

In the later phases of subacute thyroiditis, scintigraphy reveals virtually no uptake of isotope in the thyroid. Less dramatic presentations may demonstrate patchy uptake. If only one part of the thyroid gland is involved, the radioactive iodine uptake may be within the reference range.


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