Cutaneous Limb Metastasis of Colorectal Cancer Misdiagnosed as Zoster Infection

Cutaneous metastasis is a rare manifestation of internal malignancies. It usually occurs with the later progression of the disease and is associated with a poor prognosis. Common culprits of skin metastasis include lung cancer, melanoma, and colorectal cancer in men and breast cancer, colorectal cancer, and melanoma in women. Given these points, there is a low rate of cutaneous metastasis of colorectal cancer. When present, the most common sites include the abdominal wall and, less frequently, the face and the scalp. Rarely there is cutaneous metastasis to the upper extremity. Herein, we report the case of a female patient in her 50s who presented with a maculopapular rash of the right upper limb four years after her initial diagnosis of colonic adenocarcinoma. However, because of this rare manifestation, she was initially misdiagnosed with more common causes of a maculopapular rash. After a period of no improvement with preliminary treatment, a biopsy with immunohistochemical staining was undertaken, and the specimen stained positive for CK20 and CDX2, confirming metastatic colorectal malignancy. Skin lesions that are not responding to conventional therapy and those which have bizarre presentations can be a harbinger of internal malignancy and should be considered in the differential.