99mTc-sestamibi thyroid uptake in euthyroid individuals and in patients with autoimmune thyroid disease

We investigated the biokinetics of (99m)Tc-sestamibi in the thyroid of euthyroid volunteers (EVs) and in patients with autoimmune thyroid diseases and determined the best time interval between (99m)Tc-sestamibi injection and calculation of uptake.

Forty EVs, 30 patients with Graves' disease (GD), 15 patients with atrophic Hashimoto's thyroiditis (AHT) and 15 patients with hypertrophic Hashimoto's thyroiditis (HHT) underwent (99m)Tc-sestamibi thyroid scintigraphy. Dynamic images were acquired for 20 min, and static images were obtained 20 min, 60 min and 120 min post injection. Five-, 20-, 60- and 120-min uptake, time to maximal uptake (T(max)) and T(1/2) of tracer clearance were calculated. Thyroid hormones and antibodies were measured. (99m)Tc-pertechnetate uptake was investigated in GD patients.

T(max) was approximately 5 min in all four groups. The mean T(1/2) value for EVs was similar to the GD value and lower than the HHT and AHT values. The mean (+/-SD) 5-min uptake was 0.13% (+/-0.05%) for EVs. The 5-min uptake in GD was higher than that in EVs(P<0.001) and correlated with free thyroxine (r=0.54) and with (99m)Tc-pertechnetate uptake (r=0.68). Uptake in HHT was higher than that in AHT (P=0.0003) and EVs (P=0.002). Uptake in AHT was lower than uptake in EVs (P=0.0001).

Five minutes is the optimal time interval between (99m)Tc-sestamibi injection and calculation of thyroid uptake. Five-minute uptake differentiates euthyroid individuals from GD patients. There is a high correlation between (99m)Tc-sestamibi and (99m)Tc-pertechnetate uptake in GD. The reduced (99m)Tc-sestamibi uptake in AHT patients is probably due to glandular destruction and fibrosis. Inflammatory infiltrate and high mitochondrial density in thyrocytes possibly explain the increased uptake in GD and HHT.