Purpose: Published data on recombinant human thyrotropin- (rhTSH-) stimulated iodine-123 (¹²³I) diagnostic whole-body scintigraphy (DxWBS) in differentiated thyroid cancer (DTC) surveillance after initial treatment are limited. We sought to evaluate this modality's diagnostic value in this setting.
Materials and methods: We retrospectively compared rhTSH-stimulated ¹²³I DxWBS results with DTC status concurrently determined by stimulated serum thyroglobulin (Tg) measurement, neck ultrasonography, and other imaging studies. Disease was considered present based on stimulated Tg level ≥1 μg/L without interfering Tg autoantibodies with or without positive imaging or biopsy-proven DTC. We also compared scan positivity and disease detection rates of rhTSH-stimulated DxWBS scans obtained with ¹²³I with those acquired with iodine-131 (¹³¹I) during the same period. The sample comprised 105 consecutive totally thyroidectomized patients undergoing rhTSH-aided DxWBS with I-123 (n = 67) or with ¹³¹I (n = 38) for diagnostic follow-up. rhTSH, 0.9 mg/d, was injected intramuscularly on 2 consecutive days. Oral diagnostic activities of 5 to 10 mCi (185-370 MBq) ¹²³I or 3 mCi (111 MBq) ¹³¹I were given on the third day. DxWBS was performed 24 hours (¹²³I) or 48 to 72 hours (¹³¹I) later.
Results: rhTSH-aided ¹²³I DxWBS scans showed 35.3% sensitivity, 98.0% specificity, 85.7% positive predictive value, and 81.6% negative predictive value. rhTSH-stimulated ¹²³I and ¹³¹I DxWBS did not differ in scan positivity (10.4% vs. 13.2%, P = 0.75) or disease detection rates (35.3% vs. 27.8%, P = 1.00).
Conclusions: In DTC, rhTSH-aided ¹²³I DxWBS achieves comparable results in diagnostic follow-up with those of rhTSH-aided ¹³¹I DxWBS. Future studies should address the preablation setting and scan activity and timing.