Papillary Thyroid Microcarcinoma with Lung Metastases: A Case Report and Review of the Literature

Distant metastasis from papillary thyroid microcarcinoma (PTMC) is rare. Here we report a case of PTMC with multiple lung metastases. A 64-year-old man presented to our hospital with abdominal pain. Computed tomography incidentally revealed multiple lung nodules. The lung tumor was histologically diagnosed as metastasis of papillary thyroid carcinoma (PTC) by core needle biopsy via thoracoscopy. The patient was referred to our department for further examination. Neck ultrasonography revealed a 0.9 cm hypoechoic nodule in the right lobe of the thyroid gland, which was diagnosed as PTC by fine-needle aspiration cytology. Subsequently, total thyroidectomy was performed, followed by radioiodine therapy. Iodine-131 (131-I) scintigraphy showed a strong accumulation in the lung metastasis. The patient presented no evidence of progression of lung metastasis for 25 months after the operation. Lymph node metastasis or extraglandular extension has been reported in the few published cases of metastatic PTMC, including the present case, and the average age of these cases was 58.8 ± 12.0 years. Although active surveillance without surgical resection is expected to become a standard of care for PTMC, this case indicates that a subset of PTMC patients with risk factors may develop distant metastases. Hence, careful preoperative screening is required to avoid complications associated with completion thyroidectomy.