Abstract
To determine the predictive value of the baseline stimulated thyroglobulin (STg) level for ablation outcome in patients undergoing adjuvant remnant radioiodine ablation (RRA) for differentiated thyroid carcinoma (DTC). This retrospective study accrued 64 patients (23 male and 41 female; mean age of 40±14 years) who had total thyroidectomy followed by RRA for DTC from January 2012 till April 2014. Patients with positive anti-Tg antibodies and distant metastasis on post-ablative whole body iodine scans (TWBIS) were excluded. Baseline STg was used to predict successful ablation (follow-up STg<2 ng/ml, negative diagnostic WBIS and negative ultrasound neck) at 7-12 months follow-up. Overall, successful ablation was noted in 37 (58%) patients while ablation failed in 27 (42%). Using the ROC curve, a cut-off level of baseline STg level of ≤14.5 ng/ml was found to be most sensitive and specific for predicting successful ablation. Successful ablation was thus noted in 25/28 (89%) of patients with baseline STg≤14.5 ng/ml and 12/36 (33%) patients with baseline STg>14.5 ng/ml ((p value<0.05). Age>40 years, female gender, PTS>2 cm, papillary histopathology, positive cervical nodes and positive TWBIS were significant predictors of ablation failure. We conclude that in patients with total thyroidectomy followed by I-131 ablation for DTC, the baseline STg level is a good predictor of successful ablation based on a stringent triple negative criteria (i.e. follow-up STg <2 ng/ ml, a negative DWBIS and a negative US neck).
Highlights
Differentiated thyroid carcinomas (DTC; including papillary and follicular varieties) are the most common endocrine malignancy with 10 years survival around 90% (Lin et al, 2011; Budak et al, 2013)
We conclude that in patients with total thyroidectomy followed by I-131 ablation for DTC, the baseline Stimulated Tg level (STg) level is a good predictor of successful ablation based on a stringent triple negative criteria
All patients were treated as per following protocol: (1) after total thyroidectomy patients remained off-thyroxin for 3-4 weeks; (2) advised to have low iodine diet for at least 2 weeks prior to radioiodine-131 remnant ablation (RRA); (3) 2-3 days prior RRA they had, baseline stimulated TSH, STg, and Anti-Thyroglobulin antibodies; (5) I-131(as sodium iodide) in liquid form was administered orally and patients were kept in isolation as per local statutory guidelines; (6) therapy whole body iodine scan (TWBIS) was performed 3 to 5 days after RRA; (7) they were started on thyroxin 72 hours after RRA to suppress TSH; (8) 7-12 months after RRA, they had their sTSH, STg, anti-Tg-ab, neck ultrasound, and diagnostic whole body iodine scan (DWBIS) after stopping thyroxin for 18-24 days
Summary
Differentiated thyroid carcinomas (DTC; including papillary and follicular varieties) are the most common endocrine malignancy with 10 years survival around 90% (Lin et al, 2011; Budak et al, 2013) This outcome is ensured by total thyroidectomy, radioiodine-131 remnant ablation (except in patients with unifocal or multifocal lesion≤1 cm in size) and lifelong thyroxin suppressive therapy (Pacini et al, 2006; Cooper et al, 2009). To determine the predictive value of the baseline stimulated thyroglobulin (STg) level for ablation outcome in patients undergoing adjuvant remnant radioiodine ablation (RRA) for differentiated thyroid carcinoma (DTC). Conclusions: We conclude that in patients with total thyroidectomy followed by I-131 ablation for DTC, the baseline STg level is a good predictor of successful ablation based on a stringent triple negative criteria (i.e. follow-up STg < 2 ng/ ml, a negative DWBIS and a negative US neck)
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