Papillary and follicular thyroid carcinoma metastatic to the skin: a case report and review of the literature.

Cutaneous metastases from thyroid cancers are rare. We report the case of an otherwise asymptomatic 81-year-old woman with an enlarging scalp lesion. Her solitary skin metastasis was the presenting feature of thyroid carcinoma. Routine histopathology of the lesion was notable for an atypical clear cell neoplasm. Immunohistochemistry was positive for thyroglobulin. Subsequent resection of the thyroid gland identified separate foci (< 1 cm) for both papillary and follicular carcinoma. Although such immunohistochemical staining has been used previously, it has never been reported to provide the definitive diagnosis for a solitary cutaneous metastasis from the thyroid. Previous tumors had anatomic features in a clinical context that permitted identification by routine light microscopy. Clear cell features found in the follicular focus of carcinoma in the thyroid suggest that it is the primary. A worldwide literature review reveals that follicular carcinoma has a greater preponderance than papillary carcinoma for cutaneous metastasis and that the majority of skin metastases from either papillary or follicular thyroid cancer are localized to the head and neck.