Background: Patients being treated for differentiated thyroid cancer (DTC) receive a dose of Radioiodine for remnant ablation. Occasional patients appear to have little or no iodine uptake at all in the thyroid bed or else where even shortly after thyroidectomy.
Objective: To evaluate the influence of Coexisting Thyroiditis on radioiodine uptake in thyroid cancer ablation doses.
Methods and Design: Retrospective study of 240 DTC patients who received I-131 remnant ablation, out of which 165 patients met the inclusion criteria. We compared Radioiodine uptake on the nuclear medicine tail-end scan with initial histopathology reports and thyroid autoantibody status. High risk determinants such as lymph node metastasis and extrathyroidal extension were evaluated.
Results: Out of 165 DTC patients 52 (30.7%) had coexisting thyroiditis. Out of 52 patients with thyroiditis, 28 (53.8%) showed poor uptake on the tail end scan compared to those without thyroiditis. P=0.000. Patients with thyroiditis also demonstrated low level of extrathyroid extension (17.6%) and lymph node metastasis (34.6%) compared to DTC without thyroiditis. P values 0.003 and 0.064 respectively.
A total of 135 were analysed based on low (1100 MBq) and high (3000 MBq) doses. 98 received 1100 MBq. 13 (37.1%) out of 35 with thyroiditis showed poor uptake while 22 (62.8%) had intense uptake compared to 63 without thyroiditis in the same group 0 (10.6%) poor uptake. (P<0.001)
Of the 36 patients in 3000 MBq group, 5 (33.3%) out of 15 with thyroiditis showed poor uptake and 10 (66.6%) showed intense uptake compared to 0% poor uptake and 100% intense uptake in those without thyroiditis. (P=0.008)
Conclusion: This study demonstrated Thyroiditis effectively inhibited radioiodine uptake in low ablation doses. It was also shown that this beneficial effect brought about by background thyroiditis was overcome by administering higher dose RAI.
Keywords: Differentiated Thyroid cancer, Thyroiditis, Recurrence, Radioiodine, Ablation dose.