Short-term follow-up US leads to higher false-positive results without detection of structural recurrences in PTMC

To investigate the value of the annual follow-up neck ultrasonography (US) for postoperative surveillance in patients with papillary thyroid microcarcinoma (PTMC). This retrospective study has been approved by our institutional review board (IRB) with waiver for informed consent. A total of 375 patients diagnosed as PTMCs, who underwent total thyroidectomy with radioiodine remnant ablation were included, to identify the recurrence rate and the false-positive rate of annual ultrasound. The number, interval, and the results of follow-up US or fine needle aspiration were obtained from electronic medical records. Four (1.1%, 4/375) recurrences were found 3 years after the initial treatment, and only 1 patient (0.3%, 1/375) had a metastatic lymph node larger than 8mm in the shortest diameter on US found 7.6 years after initial treatment with biochemical abnormalities. Cumulative risk of having at least 1 false-positive exam was 8.3% by the 8th US, and 8.1% by the 8-9 year follow-up. Cox multivariate regression showed shorter interval of follow-up US and presence of lymph node metastasis at initial surgery are independent predictors affecting the cumulative falsepositive results (hazard ratio [HR], 0.60; 95% confidence interval [CI]: 0.49-0.73; P<0.001 and HR, 2.19; 95% CI: 1.01-4.75; P=0.048, respectively). Short-term follow-up US can result in higher cumulative falsepositive results without detection of meaningful recurrences in patients with PTMCs who do not have biochemical abnormalities.