Thyroid carcinoma and focal lymphocytic thyroiditis share common features in ultrasonography : a diagnostic predictor model for discrimination

Abstract

Background:Thyroid carcinoma is suspected when a nodule shows suspicious ultrasound (US) features. However, it is often difficult to discriminate focal lymphocytic thyroiditis (FLT) from thyroid carcinoma because of similar US findings. The objective was to discriminate FLT from thyroid carcinoma.Methods:One hundred thirty patients had undergone fine-needle aspiration biopsy (FNAB) and had shown thyroid nodules with suspicious US features. Papillary thyroid carcinoma (PTC) was confirmed by postoperative histology and FLT was confirmed through at least 2 FNAB. Clinical and biochemical findings, and US features were evaluated.Results:One hundred patients (76.9%) had PTC and 30 patients (23.1%) had FLT. US showed that the absence of calcification or “diffuse thyroid disease” (DTD) pattern was more common in patients with FLT than with PTC (P<0.001). The median TSH level was higher in FLT than PTC patients (P=0.016). The prevalence of antithyroid peroxidase antibody (TPO-Ab) or antithyroglobulin antibody (Tg-Ab) was more frequent in FLT than in PTC patients (P<0.001). To discriminate FLT from PTC, I created a diagnostic predictor model using logistic regression which included TSH, TPO- or Tg-Ab positivity, calcification, and DTD pattern. The model’s predictor probability of FLT rather than PTC was 85.4%.Conclusion:In patients presenting a thyroid nodule with suspicious US features, FLT is more likely than PTC when the nodule lacks calcification or is accompanied by a DTD pattern, the TSH level is  2.5 IU/dL, and the patient is the patient is TPO- or Tg-Ab positive.