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

Purpose We investigated the biokinetics of ^99mTc-sestamibi in the thyroid of euthyroid volunteers (EVs) and in patients with autoimmune thyroid diseases and determined the best time interval between ^99mTc-sestamibi injection and calculation of uptake.Methods Forty EVs, 30 patients with Graves disease (GD), 15 patients with atrophic Hashimotos thyroiditis (AHT) and 15 patients with hypertrophic Hashimotos thyroiditis (HHT) underwent ^99mTc-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. ^99mTc-pertechnetate uptake was investigated in GD patients.Results 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 ^99mTc-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).Conclusion Five minutes is the optimal time interval between ^99mTc-sestamibi injection and calculation of thyroid uptake. Five-minute uptake differentiates euthyroid individuals from GD patients. There is a high correlation between ^99mTc-sestamibi and ^99mTc-pertechnetate uptake in GD. The reduced ^99mTc-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.