A comparison study of remnant thyroid gland using salivary scintigraphy with post-ablation I-131 scan

Objectives In this study, we investigated the correlation between 99mTc pertechnetate uptake in remnant thyroid in pre-ablative salivary scintigraphy with 131-Iodine uptake in Post-Therapy Scan (RAI scan).

Methods A total of 282 patients who underwent high dose RAI (150-200mCi) from 2008 to 2013 were enrolled in this study. Thyroid pathology slides were reviewed to evaluate for thyroiditis. All salivary scintigraphy were performed 2 to 3hours prior to radioiodine administration. Post-Therapy scans were performed 2-3 days on discharge. Visual grading of remnant thyroids in salivary scintigraphy is evaluated grade 0 to 4(0 = no uptake, 1 = mininal uptake, 2 = mild uptake, 3 = moderate uptake, 4 = intense uptake). Visual grading of remnant thyroids in RAI scans is divided grade 0 to 4(0 = no uptake, 1 = minimal uptake, 2 = mild uptake, 3 = moderate uptake, 4 = star artifact)

Results In salivary scintigraphy visual analysis, there were 73(25.9%) grade 0, 73(25.9%) grade 1, 52 grade 2(18.4%), 57(20.2%) grade 3, and 27(9.6%) grade 4 patients. In RAI scan, there were 7(2.5%) grade 0, 17(6.0%) grade 1, 32(36.6%) grade 2, 123(43.6%) grade 3, and 103(36.5%) grade 4 patients. There was a statistically significant trend for increased visualization of the thyroid gland in salivary scan compared to RAI scans (x2 for trend, p<0.001). When salivary and RAI scans were dichotomized into visualized to non-visualized thyroid uptake, salivary scan was 76.6% accurate (209 true positive, 7 true negative) compared to RAI scans, with 66 patients (23.4%) as false negative compared to RAI scans (x2, p<0.001)

Conclusions Salivary scintigraphy showed a strong positive correlation with RAI scans in evaluation of thyroid gland function, and thyroiditis was shown to be an important factor in discordance between the two scans.