Are there disadvantages in administering 131I ablation therapy in patients with differentiated thyroid carcinoma without a preablative diagnostic 131I whole-body scan?

OBJECTIVE: To evaluate the risk of performing inappropriate (131)I ablative therapies for thyroid carcinoma in patients lacking thyroid remnants or metastases, using a strategy of treatment without a preliminary iodine-131 diagnostic whole-body scan (DxWBS).

DESIGN: Retrospective evaluation of post-therapy whole-body scans to assess the prevalence of thyroid remnants or metastases after total thyroidectomy. Comparison of (131)I uptake test and thyroglobulin (Tg) off levothyroxine (L-T4) performed before therapy with post-therapy scans, in order to evaluate the ability to predict inappropriate treatments.

PATIENTS: A group of 875 consecutive patients with previous total or near-total thyroidectomy for differentiated thyroid carcinoma underwent (131)I ablative therapy without a preliminary (131)I-DxWBS. All patients were clinically free of distant metastases and macroscopic residual tumour.

MEASUREMENTS: Whole-body scans were performed 2-5 days after the treatment as gold standard for thyroid remnants and metastases; 24-h (131)I quantitative neck uptake test and Tg off L-T4 were performed before (131)I therapy.

RESULTS: The majority of patients (94%) were found to have thyroid remnants or metastases at post-therapy scans, in most cases (91.2%) with detectable Tg off L-T4 and positive 24-h neck uptake. 14 patients (1.6%) with tiny lymph-node metastases positive at post-therapy scans showed undetectable Tg off L-T4. In 30 patients (3.6%) faint positive post-therapy images for thyroid remnants have been classified as false-positive results on the basis of both negative 24-h neck uptake and undetectable Tg off L-T4.

CONCLUSIONS: This study confirms that most patients have residual thyroid tissue after total thyroidectomy and that it seems reasonable to omit routine diagnostic whole-body scans before (131)I treatment with clinical, managerial and economic advantages.