Submerged goiter proven to be metastatic infiltration of a neuro-endocrine Merkel cell carcinoma

BACKGROUND: Merkel cell carcinoma (MCC) is an uncommon neuroendocrine cutaneous carcinoma. Metastases to the thyroid gland are rare and may present diagnostic difficulties. CASE PRESENTATION: A 73-year-old woman presented with a hard mass in the adipose tissue of the right inguinal area. This mass was surgically excised and the histology examination showed the existence of a MCC. CT scans revealed a sizable lesion with imaging features of a submerged goiter, invasive to the upper mediastinum. The patient received chemotherapy following by locoregional radiotherapy at the bed of the excised lesion. During the next 10 months the patient was asymptomatic, serum markers values were normal and CT scans findings were stable. However, afterwards NSE and chromogranin values raised and CT scans revealed an enlargement of the submerged goiter. The patient became symptomatic, mainly experiencing respiratory inconvenience. Surgical excision of the right lobe of the thyroid gland was decided and performed without any complications. The histopathology examination showed infiltration of the thyroid gland by a neuroendocrine carcinoma with characteristics compatible with MCC. CONCLUSIONS: The rare case of metastatic infiltration of the thyroid gland by a MCC based on histological and immunohistochemical findings was described. This case report is of clinical significance indicating that by any abnormal finding in the thyroid gland in patients with a malignant disease, the diagnostic approach should always contain consideration of metastasis from the primary tumor.