Anaplastic thyroid cancer manifesting as new-onset Horner syndrome.

OBJECTIVE: To report a case of Horner syndrome as the initial sign of locally advanced anaplastic thyroid cancer.
METHODS: We present a case report in conjunction with a retrospective review and evaluation of the English-language literature on Horner syndrome and thyroid pathologic conditions.
RESULTS: Horner syndrome is a rare complication of thyroid disease most often occurring in the postoperative setting after resections. Preoperatively, Horner syndrome is usually caused by a benign intrathoracic goiter that compresses the sympathetic plexus as it exits the thoracic cavity to enter the neck. Malignant thyroid disease leading to Horner syndrome is less common than benign causes of the syndrome. Treatment of compressive lesions can lead to resolution of nerve compression.
CONCLUSION: Horner syndrome is a rare complication of thyroid pathologic conditions. When present preoperatively, the majority of cases are due to benign compression of the cervical plexus. Therefore, Horner syndrome in the setting of a goiter does not necessarily portend a malignant process as one might suspect. Nonetheless, it still remains important that those patients who present with Horner syndrome undergo appropriate assessment for detection of mass lesions, underlying vascular etiologic factors, or other potentially treatable disorders causing sympathetic chain dysfunction.