Destructive (Subacute) Thyroiditis

Destructive (subacute) thyroiditis may be caused by autoimmune disease, viral infection, or iodine overload (e.g., type II amiodarone-induced thyrotoxicosis). Viral infection is usually associated with a painful goiter, while autoimmune thyroiditis is usually painless.

The main differential consideration is iodine-induced hyperthyroidism (the Jod-Basedow effect, e.g., type I amiodarone-induced thyrotoxicosis). Scintigraphic features may mimic those of subacute thyroiditis; however, low-normal thyroid uptake (as opposed to very low) suggests Jod-Basedow effect.

The appearance of diffusely decreased thyroid uptake may also be seen with:

• Hypothyroidism:
• Medications: Amiodarone, iodinated contrast.
• Thyroid hormone therapy:
• Renal failure: Iodide excretion is diminished in advanced renal failure, leading to an increased iodide pool in the thyroid and diminished uptake of radiolabeled iodide by the thyroid.
• Ectopic thyroid hormone secretion from tumors: Struma ovarii ("ovarian goiter").

Our patient has hyperthyroidism with positive antithyroid antibodies. This image from an I-123 study shows diffusely decreased thyroid uptake. 4-hour and 24-hour uptake values were very low (1.2% and 3.5%, respectively).

References

Sarkar SD. Benign thyroid disease: what is the role of nuclear medicine? Semin Nucl Med. 2006 Jul;36(3):185-93.