Right leg swelling as primary presentation of metastatic Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a rare malignant cutaneous neuroendocrine tumour with an aggressive behaviour and frequent regional lymph node and distant metastases. It mostly occurs in old patients and the commonest sites are the skin of the head, neck and the extremities. Typically, the primary tumour presents as a fast-growing, painless, reddish nodule with an iceberg-like effect, broadening in the depth. Although the pathogenesis of MCC remains largely unknown, ultraviolet radiation and immunosuppression are likely to play a significant pathogenetic role. The authors describe an unusual case of MCC clinically presenting as lymphedema on the right leg due to an inguinal lymphonodal metastasis. Although extensive investigations were performed the authors were unable to discover the cutaneous primary tumor. The authors examine the etiopathogenesis and hypothesis of this rare tumour and describe the clinical differential diagnosis. They suggest that clinical features together with imaging studies and morphological and immuno-histochemical findings are important for the correct diagnosis.