Merkel cell carcinoma: an aggressive cutaneous carcinoma with rare metastasis to the thyroid gland

Merkel cell carcinoma (MCC) is an aggressive and rare neuroendocrine cutaneous carcinoma with poor prognosis and with increasing morbidity and mortality in cases of distant metastasis. Given the rarity of MCC, optimal treatment is not well established. Treatment usually consists of multidisciplinary management with local excision of the primary tumour. Imaging studies are essential for accurate staging and monitoring of disease progression. The incidence of local recurrence is highest in the first 2 years and ranges from 27% to 60%. Distant metastasis is most common in the skin, liver, bone, lung/pleura, brain or distant lymph nodes. The thyroid gland is a rare site of metastasis for MCC with only two case reports published to date. Our patient had a repeat 2-[18F]-fluoro-2-deoxy-d-glucose-postiron emission tomography/CT after the discovery of recurrence of MCC. The high-intensity maximal standardised uptake value of 10.9 in the thyroid isthmus is consistent with malignancy. This case report describes an exceedingly rare thyroid metastasis secondary to MCC.