Introduction: I131 whole body scan (WBS) is used in follow–up of patients with well differentiated thyroid cancer (WDTC) post total thyroidectomy and I131 ablation therapy. Traditionally, it is performed after withdrawal of Thyroxine (T4) for at least 4-6 weeks to stimulate endogenous TSH to a level more than 30mIU/L. T4 withdrawal is associated with significant symptoms of hypothyroidism. In clinical practice, several studies report that serum TSH rapidly reaches the level of >30mIU/L at a mean of 17 to 18.1 days after T4 withdrawal in 96.2% of patients, reducing the duration of hypothyroidism and improving acceptance of scanning with I131 with minimal impact on health related quality of life (QOL).
Aim of the study: The aim of the current study is to compare effects of T4 withdrawal for 3 weeks versus traditional withdrawal for 4 weeks on serum TSH level and hypothyroid symptoms in patients with WDTC presenting for I131 follow up WBS post total thyroidectomy and successful I131 ablation therapy.
Patients and methods: One hundred patients with WDTC presented for I131 WBS post successful complete ablation of residual functioning thyroid tissue in the neck, all had suppressed or within normal TSH level. They were divided into 2 equal groups. Group I, instructed to withdraw Thyroxine for 3 weeks and group II, instructed to stop thyroxine for 4 weeks. Serum TSH level was estimated for all patients prior to oral intake of I131. Also, a questionnaire of main hypothyroid symptoms was filled by all patients about presence or absence of the symptoms and their severities that were divided into mild, moderate and severe.
Results: For group I, 49 patients (98%) had TSH level >30 mIU/ml (mean=77.4±27.9), while all patients in group II (100%) achieved significantly higher TSH level (mean=119.1±42.1). There was a highly significant positive correlation (p<0.001) between number of symptoms and late serum TSH level within each group. The number of symptomatic patients was 39 patients (78%) in group I having a total number of 100 symptoms, with a mean of 2.0±1.5; out of them 60 mild, 29 moderate and 11 severe representing 60%, 29% and 11%, respectively. While for group II, number of polysymptomatic patients was 46(92%) with a total number of 233 symptoms with a mean of 4.7±2.6; out of them 70 mild, 95 moderate and 68 severe representing 30%, 40.8% and 29.2%, respectively. Patients in group I had significantly less hypothyroidism as regards number of patients, number of symptoms and their severity compared to group II. Moreover, a significant positive correlation between number of hypothyroid symptoms and serum TSH level was detected in both groups. Conclusion: It is concluded to withdraw thyroxine for 3 weeks instead of 4 weeks for patients with well differentiated thyroid carcinoma prior to regular follow up I131 WBS to achieve the desired serum TSH level with significantly less hypothyroid symptoms and better quality of life.