Thyroid Stunning – A Myth Or A Reality & Does It Adversely Affect The Treatment Outcome In Differentiated Thyroid Cancers? Volume 7 - Issue 4

P Shanmuga Sundaram* and Subramanyam Padma

• Clinical Professors, Department of Nuclear Medicine & Molecular Imaging, Amrita Institute of Medical Sciences & Research Centre, Amrita Vishwa vidyapeetham University, Kerala, India

Received: November 15, 2021;   Published: November 30, 2021

Corresponding author: P Shanmuga Sundaram, Clinical Professor, Department of Nuclear Medicine & Molecular Imaging, Amrita Institute of Medical Sciences & Research Centre, India

DOI: 10.32474/SJO.2021.07.000270

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Abstract

Radio iodine (131 I) is a well-established diagnostic and therapeutic tool that is very effective in differentiated thyroid carcinoma (DTC) with and without metastases. Stunning of thyroid tissue is a visual phenomenon often described in post therapy 131 I patients after undergoing 131 I whole body (WBI) diagnostic scans. It may be defined as a temporary suppression of iodine trapping function of the thyrocytes and thyroid cancer cells as a result of the radiation given off by the scanning (or first) dose of 131 I. In other words, there is non-visualization of 131 I concentrating thyroid remnant or distant metastases which was in fact present in the pretherapy (diagnostic) scan. This phenomenon is still controversial, and few suggest that it could influence the efficacy of high dose 131 I therapy, making it unsuccessful. However, the underlying mechanism still remains unclear.
Aim: Firstly, to determine the various factors that can lead to thyroid stunning in DTC patients. Secondly, is there a reduced therapeutic efficacy of the therapeutic dose that affects the final treatment outcome.
Materials & Methods: This retrospective study was conducted in a tertiary care university hospital with data obtained from 227 DTC patients (Male: female = 34: 193, Age range: 16 – 78 yrs, Median age: 40 years). Majority of patients were papillary thyroid carcinomas. All patients underwent thyroidectomy, diagnostic WBI scans followed by high dose 131 I therapy.
Results: Based on post therapy WBI scan findings, patients were categorized into two groups, with stunning and no stunning effect. Patients were on regular follow up (mean 24 ± 3 months) and underwent WBI scan, serum thyroglobulin (Tg), anti Tg antibody. Statistical analysis was done with Fischer’s exact test and 2 tailed p values were calculated. No statistically significant difference in the treatment outcome between both groups was observed.
Conclusion: Our study concludes that thyroid stunning is indeed only a visual phenomenon encountered in 17.62% of our DTC patients undergoing high dose 131 I therapy. It however does not affect the therapeutic outcome even in those patients who demonstrated stunning in post therapy WBI scans substantiated by undetectable or stimulated Tg value <2ng/ml. Of the various factors studied, it has been found that dose and timing of therapy after diagnostic I 131 scan are most important. Doses as low as 1.5 mCi of I 131 also demonstrate stunning effect. Other factors that are found to influence the occurrence of stunning are delay between diagnostic scan and therapy, time between treatment and post therapy WBI scan, and timing of follow-up scans.

Keywords: Differentiated thyroid cancer; 131 I whole body scan; Post therapy WBI scan; thyroid stunning

Abstract| Introduction| Materials & Methods| Results| Discussion| Conclusion| Acknowledgements| Conflicts of Interest| References|