Tc-99m pertechnetate trapping and thyroid function in Hashimoto's thyroiditis.

Tc-99m pertechnetate thyroid imaging was studied in 52 patients with Hashimoto's thyroiditis, with special reference to the thyroid functional state and Tc-99m trapping by the gland. The most common finding was diffusely increased trapping of radioactivity, a pattern similar to Graves' disease. On the other hand, the increased trapping in Hashimoto's thyroiditis was usually associated with hypothyroidism. The degree of Tc-99m trapping did not correlate with the degree of the endogenous TSH elevation. However, increased Tc-99m trapping could predict the reversibility of hypothyroidism in just 3 months.