Acute suppurative thyroiditis caused by thyroid papillary carcinoma in the right thyroid lobe of a healthy woman.

Background: The thyroid gland is resistant to microbial infection, because of its organ characteristics such as encapsulation, iodine content, and rich blood supply. Therefore, acute suppurative thyroiditis (AST), as a bacterial infection of the thyroid gland, is rarely seen. AST typically takes places on the left side the neck region in children, because of the coincidence of the left piriform sinus fistula, as a most common route of infection. AST is also usually seen in immunocompromised hosts. Herein, we report a rare case of AST in the right thyroid lobe of adult woman without any immunocompromised condition.

Case presentation: A 59-year-old woman was introduced to our hospital for the further examination with fever, sore throat, and right anterior neck swelling. The patient appeared not to be immunodeficient. Neck ultrasonography showed a 47-mm, hypoechoic, heterogeneous nodule with ill-defined margins and irregular form, suggesting a right thyroid malignant nodule. Fine needle aspiration (FNA) biopsy specimen revealed numerous number of neutrophils in the background without nuclear atypia. Based on the clinical course and cytology, AST was confirmed to be diagnosed. Complete response was obtained by an intravenous administration of antimicrobial agents within a week. Image findings such as CT scan did not show any piriform sinus fistula. Four months later, neck ultrasonography showed a significant decrease in size of the nodule in the right thyroid gland to 27 mm, but the lesion still resembled a malignant nodule. So, FNA was repeated again and cytological examination confirmed papillary thyroid carcinoma (PTC). The patient subsequently underwent total thyroidectomy and bilateral level D1 lymph node dissection. Histological findings revealed a 20-mm PTC in the right lobe with sternothyroid muscle invasion of the tumor.

Conclusions: This report represents a rare case of AST associated with PTC on the right side of thyroid gland, found in a healthy adult woman. The reason why AST coincided with malignant thyroid tumor is unclear. We have to take it into our account that malignant tumor may exist in the background when AST is identified on the right side of thyroid gland with a healthy subject.