Clinical and pathologic predictors of lymph node metastasis in papillary thyroid microcarcinomas

Papillary thyroid microcarcinoma (PTMC) has the highest incidence among all thyroid carcinomas. Although surgery is the primary treatment for PTMC, it inevitably leads to trauma and some complications. To formulate an optimal treatment strategy, we aim to clarify the risk factors for lymph node metastasis (LNM) in PTMC patients. This study retrospectively analyzed patients who underwent thyroidectomy during 1995-2015, and grouped them according to lymph node metastasis. Age, gender, tumor size, thyroid functions, Hashimoto's thyroiditis, multifocal tumor, extrathyroidal extensions, capsular invasion were analyzed. Of the 2434 PTMC subjects, proportion of patients with no LNM (NLNM), LNM, central LNM (CLNM), lateral LNM (LLNM), CLNM + LLNM were 82.9%, 17.1%, 7.0%, 7.6% and 2.5%. Patients with NLNM were older and had a lower proportion of males compared to patients with CLNM, LLNM and CLNM + LLNM (p < 0.05). The NLNM group also had a smaller size of ultrasound tumor, lower proportion of multifocal tumor and extrathyroidal extension compared to CLNM, LLNM and CLNM + LLNM groups (p < 0.05). On univariate analyses, male gender, age <45 years, tumor size of pathology (˃0.75 cm), multifocality, and extrathyroidal extension were significantly associated with LNM. Multivariate analyses revealed that male gender, age <45 years, multifocality were risk factors for LNM. In conclusion, PTMC patients with male gender, age <45 years and multifocality should be evaluated carefully for possible LNM.