A systematic review of the incidence of thyroid carcinoma in patients undergoing thyroidectomy for thyrotoxicosis.

INTRODUCTION: Hyperthyroidism (HT) has been associated with no insignificant rates of thyroid malignancy. There are no current specific guidelines that suggest routine preoperative imaging for thyroid nodules in patients with Grave's disease. We therefore performed a systematic review assessing rates of thyroid malignancy in patients undergoing surgery for different causes of HT: Grave's disease (GD), toxic adenoma (TA) and toxic multinodular goitre (TMNG).

METHODS: Major databases (MEDLINE, PubMed and the Cochrane library) were searched to identify eligible studies.

RESULTS: After searching and appraising, 33 papers were found to be eligible for analysis. The mean overall rate of malignancy was 8.5% (range 0.8%-32.4%). The mean rates based on histological subtype were as follows: papillary thyroid cancer (PTC), 3.1% (range 0%-13.2%); micropapillary carcinoma (mPTC), 5.1% (range 0%-16.9%); and follicular thyroid cancer (FTC), 0.8% (range 0%-4.4%). In those patients who had preoperative imaging, mean malignancy rates were higher in patients with pre-identified nodules (19.8%) compared to those without any nodules (8.7%). Mean rates were lower in patients with GD/diffuse goitre (5.9%) compared to patients with TA (6.5%) and TMNG (12%).

CONCLUSION: Hyperthyroidism is associated with notable rates of thyroid cancer, although the mechanisms for this are not clear. The presence of nodules increases this risk. This review raises the question for considering preoperative assessment of nodules in all patients undergoing surgery for HT, in order to correctly assess and evaluate any patients with suspected concurrent thyroid malignancy, before proceeding with surgery.